[Kotlin] client improvement / remove WildCards in client/server (#2862)

2024-11-06 10:35:25 +00:00 · 2019-05-11 05:42:11 +02:00 · 2019-05-11 05:42:11 +02:00 · ef26ce68d4
commit ef26ce68d4
parent 9323cad06b
58 changed files with 656 additions and 340 deletions
--- a/.gitignore
+++ b/.gitignore
@ -175,12 +175,14 @@ samples/client/petstore/typescript-angular/tsd-debug.log
 # aspnetcore
 samples/server/petstore/aspnetcore/.vs/
 effective.pom
+
 # kotlin
 samples/client/petstore/kotlin/src/main/kotlin/test/
 samples/client/petstore/kotlin-threetenbp/build
 samples/client/petstore/kotlin-string/build
-samples/server/petstore/kotlin-server/ktor/build
 samples/openapi3/client/petstore/kotlin/build
+samples/server/petstore/kotlin-server/ktor/build
+samples/server/petstore/kotlin-springboot/build
 \?

 # haskell
--- a/docs/generators/kotlin-server.md
+++ b/docs/generators/kotlin-server.md
@ -8,14 +8,14 @@ sidebar_label: kotlin-server
 | Option | Description | Values | Default |
 | ------ | ----------- | ------ | ------- |
 |sourceFolder|source folder for generated code| |src/main/kotlin|
-|packageName|Generated artifact package name.| |org.openapitools|
+|packageName|Generated artifact package name.| |org.openapitools.server|
 |apiSuffix|suffix for api classes| |Api|
 |groupId|Generated artifact package's organization (i.e. maven groupId).| |org.openapitools|
-|artifactId|Generated artifact id (name of jar).| |null|
+|artifactId|Generated artifact id (name of jar).| |kotlin-server|
 |artifactVersion|Generated artifact's package version.| |1.0.0|
 |enumPropertyNaming|Naming convention for enum properties: 'camelCase', 'PascalCase', 'snake_case', 'UPPERCASE', and 'original'| |camelCase|
 |parcelizeModels|toggle &quot;@Parcelize&quot; for generated models| |null|
-|library|library template (sub-template) to use|<dl><dt>**ktor**</dt><dd>ktor framework</dd><dl>|ktor|
+|library|library template (sub-template)|<dl><dt>**ktor**</dt><dd>ktor framework</dd><dl>|ktor|
 |featureAutoHead|Automatically provide responses to HEAD requests for existing routes that have the GET verb defined.| |true|
 |featureConditionalHeaders|Avoid sending content if client already has same content, by checking ETag or LastModified properties.| |false|
 |featureHSTS|Avoid sending content if client already has same content, by checking ETag or LastModified properties.| |true|
--- a/docs/generators/kotlin-spring.md
+++ b/docs/generators/kotlin-spring.md
@ -11,7 +11,7 @@ sidebar_label: kotlin-spring
 |packageName|Generated artifact package name.| |org.openapitools|
 |apiSuffix|suffix for api classes| |Api|
 |groupId|Generated artifact package's organization (i.e. maven groupId).| |org.openapitools|
-|artifactId|Generated artifact id (name of jar).| |null|
+|artifactId|Generated artifact id (name of jar).| |openapi-spring|
 |artifactVersion|Generated artifact's package version.| |1.0.0|
 |enumPropertyNaming|Naming convention for enum properties: 'camelCase', 'PascalCase', 'snake_case', 'UPPERCASE', and 'original'| |camelCase|
 |parcelizeModels|toggle &quot;@Parcelize&quot; for generated models| |null|
@ -26,4 +26,4 @@ sidebar_label: kotlin-spring
 |serviceInterface|generate service interfaces to go alongside controllers. In most cases this option would be used to update an existing project, so not to override implementations. Useful to help facilitate the generation gap pattern| |false|
 |serviceImplementation|generate stub service implementations that extends service interfaces. If this is set to true service interfaces will also be generated| |false|
 |useBeanValidation|Use BeanValidation API annotations to validate data types| |true|
-|library|library template (sub-template) to use|<dl><dt>**spring-boot**</dt><dd>Spring-boot Server application.</dd><dl>|spring-boot|
+|library|library template (sub-template)|<dl><dt>**spring-boot**</dt><dd>Spring-boot Server application.</dd><dl>|spring-boot|
--- a/docs/generators/kotlin.md
+++ b/docs/generators/kotlin.md
@ -8,12 +8,12 @@ sidebar_label: kotlin
 | Option | Description | Values | Default |
 | ------ | ----------- | ------ | ------- |
 |sourceFolder|source folder for generated code| |src/main/kotlin|
-|packageName|Generated artifact package name.| |org.openapitools|
+|packageName|Generated artifact package name.| |org.openapitools.client|
 |apiSuffix|suffix for api classes| |Api|
 |groupId|Generated artifact package's organization (i.e. maven groupId).| |org.openapitools|
-|artifactId|Generated artifact id (name of jar).| |null|
+|artifactId|Generated artifact id (name of jar).| |kotlin-client|
 |artifactVersion|Generated artifact's package version.| |1.0.0|
 |enumPropertyNaming|Naming convention for enum properties: 'camelCase', 'PascalCase', 'snake_case', 'UPPERCASE', and 'original'| |camelCase|
 |parcelizeModels|toggle &quot;@Parcelize&quot; for generated models| |null|
-|dateLibrary|Option. Date library to use|<dl><dt>**string**</dt><dd>String</dd><dt>**java8**</dt><dd>Java 8 native JSR310</dd><dt>**threetenbp**</dt><dd>Threetenbp</dd><dl>|null|
-|collectionType|Option. Collection type to use|<dl><dt>**array**</dt><dd>kotlin.Array</dd><dt>**list**</dt><dd>kotlin.collections.List</dd><dl>|null|
+|dateLibrary|Option. Date library to use|<dl><dt>**string**</dt><dd>String</dd><dt>**java8**</dt><dd>Java 8 native JSR310</dd><dt>**threetenbp**</dt><dd>Threetenbp</dd><dl>|java8|
+|collectionType|Option. Collection type to use|<dl><dt>**array**</dt><dd>kotlin.Array</dd><dt>**list**</dt><dd>kotlin.collections.List</dd><dl>|array|
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java
@ -102,7 +102,7 @@ public class JavaClientCodegen extends AbstractJavaCodegen
        apiPackage = "org.openapitools.client.api";
        modelPackage = "org.openapitools.client.model";

-        // clioOptions default redifinition need to be updated
+        // cliOptions default redefinition need to be updated
        updateOption(CodegenConstants.INVOKER_PACKAGE, this.getInvokerPackage());
        updateOption(CodegenConstants.ARTIFACT_ID, this.getArtifactId());
        updateOption(CodegenConstants.API_PACKAGE, apiPackage);
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinClientCodegen.java
@ -21,8 +21,6 @@ import org.openapitools.codegen.CliOption;
 import org.openapitools.codegen.CodegenConstants;
 import org.openapitools.codegen.CodegenType;
 import org.openapitools.codegen.SupportingFile;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;

 import java.io.File;
 import java.util.HashMap;
@ -32,7 +30,6 @@ public class KotlinClientCodegen extends AbstractKotlinCodegen {

    public static final String DATE_LIBRARY = "dateLibrary";
    public static final String COLLECTION_TYPE = "collectionType";
-    private static final Logger LOGGER = LoggerFactory.getLogger(KotlinClientCodegen.class);

    protected String dateLibrary = DateLibrary.JAVA8.value;
    protected String collectionType = CollectionType.ARRAY.value;
@ -69,6 +66,10 @@ public class KotlinClientCodegen extends AbstractKotlinCodegen {
        artifactId = "kotlin-client";
        packageName = "org.openapitools.client";

+        // cliOptions default redefinition need to be updated
+        updateOption(CodegenConstants.ARTIFACT_ID, this.artifactId);
+        updateOption(CodegenConstants.PACKAGE_NAME, this.packageName);
+
        outputFolder = "generated-code" + File.separator + "kotlin-client";
        modelTemplateFiles.put("model.mustache", ".kt");
        apiTemplateFiles.put("api.mustache", ".kt");
@ -78,14 +79,13 @@ public class KotlinClientCodegen extends AbstractKotlinCodegen {
        apiPackage = packageName + ".apis";
        modelPackage = packageName + ".models";

-        enumPropertyNaming = CodegenConstants.ENUM_PROPERTY_NAMING_TYPE.camelCase;
-
        CliOption dateLibrary = new CliOption(DATE_LIBRARY, "Option. Date library to use");
        Map<String, String> dateOptions = new HashMap<>();
        dateOptions.put(DateLibrary.THREETENBP.value, "Threetenbp");
        dateOptions.put(DateLibrary.STRING.value, "String");
        dateOptions.put(DateLibrary.JAVA8.value, "Java 8 native JSR310");
        dateLibrary.setEnum(dateOptions);
+        dateLibrary.setDefault(this.dateLibrary);
        cliOptions.add(dateLibrary);

        CliOption collectionType = new CliOption(COLLECTION_TYPE, "Option. Collection type to use");
@ -93,6 +93,7 @@ public class KotlinClientCodegen extends AbstractKotlinCodegen {
        collectionOptions.put(CollectionType.ARRAY.value, "kotlin.Array");
        collectionOptions.put(CollectionType.LIST.value, "kotlin.collections.List");
        collectionType.setEnum(collectionOptions);
+        collectionType.setDefault(this.collectionType);
        cliOptions.add(collectionType);
    }

--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinServerCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinServerCodegen.java
@ -62,6 +62,11 @@ public class KotlinServerCodegen extends AbstractKotlinCodegen {

        artifactId = "kotlin-server";
        packageName = "org.openapitools.server";
+
+        // cliOptions default redefinition need to be updated
+        updateOption(CodegenConstants.ARTIFACT_ID, this.artifactId);
+        updateOption(CodegenConstants.PACKAGE_NAME, this.packageName);
+
        outputFolder = "generated-code" + File.separator + "kotlin-server";
        modelTemplateFiles.put("model.mustache", ".kt");
        apiTemplateFiles.put("api.mustache", ".kt");
@ -69,10 +74,10 @@ public class KotlinServerCodegen extends AbstractKotlinCodegen {
        apiPackage = packageName + ".apis";
        modelPackage = packageName + ".models";

-        supportedLibraries.put("ktor", "ktor framework");
+        supportedLibraries.put(Constants.KTOR, "ktor framework");

        // TODO: Configurable server engine. Defaults to netty in build.gradle.
-        CliOption library = new CliOption(CodegenConstants.LIBRARY, "library template (sub-template) to use");
+        CliOption library = new CliOption(CodegenConstants.LIBRARY, CodegenConstants.LIBRARY_DESC);
        library.setDefault(DEFAULT_LIBRARY);
        library.setEnum(supportedLibraries);

@ -147,9 +152,9 @@ public class KotlinServerCodegen extends AbstractKotlinCodegen {

        // set default library to "ktor"
        if (StringUtils.isEmpty(library)) {
-            this.setLibrary("ktor");
-            additionalProperties.put(CodegenConstants.LIBRARY, "ktor");
-            LOGGER.info("`library` option is empty. Default to 'ktor'.");
+            this.setLibrary(DEFAULT_LIBRARY);
+            additionalProperties.put(CodegenConstants.LIBRARY, DEFAULT_LIBRARY);
+            LOGGER.info("`library` option is empty. Default to " + DEFAULT_LIBRARY);
        }

        if (additionalProperties.containsKey(Constants.AUTOMATIC_HEAD_REQUESTS)) {
@ -182,7 +187,7 @@ public class KotlinServerCodegen extends AbstractKotlinCodegen {
            additionalProperties.put(Constants.COMPRESSION, getCompressionFeatureEnabled());
        }

-        Boolean generateApis = additionalProperties.containsKey(CodegenConstants.GENERATE_APIS) && (Boolean)additionalProperties.get(CodegenConstants.GENERATE_APIS);
+        boolean generateApis = additionalProperties.containsKey(CodegenConstants.GENERATE_APIS) && (Boolean)additionalProperties.get(CodegenConstants.GENERATE_APIS);
        String packageFolder = (sourceFolder + File.separator + packageName).replace(".", File.separator);
        String resourcesFolder = "src/main/resources"; // not sure this can be user configurable.

@ -226,7 +231,7 @@ public class KotlinServerCodegen extends AbstractKotlinCodegen {
        if (objs.containsKey("lambda")) {
            LOGGER.warn("A property named 'lambda' already exists. Mustache lambdas renamed from 'lambda' to '_lambda'. " +
                    "You'll likely need to use a custom template, " +
-                    "see https://github.com/swagger-api/swagger-codegen#modifying-the-client-library-format. "); // TODO: update the URL
+                    "see https://github.com/OpenAPITools/openapi-generator/blob/master/docs/templating.md. ");
            objs.put("_lambda", lambdas);
        } else {
            objs.put("lambda", lambdas);
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinSpringServerCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinSpringServerCodegen.java
@ -87,6 +87,9 @@ public class KotlinSpringServerCodegen extends AbstractKotlinCodegen
        apiPackage = "org.openapitools.api";
        modelPackage = "org.openapitools.model";

+        // cliOptions default redefinition need to be updated
+        updateOption(CodegenConstants.ARTIFACT_ID, this.artifactId);
+
        // Use lists instead of arrays
        typeMapping.put("array", "List");
        typeMapping.put("string", "String");
@ -149,7 +152,7 @@ public class KotlinSpringServerCodegen extends AbstractKotlinCodegen
        supportedLibraries.put(SPRING_BOOT, "Spring-boot Server application.");
        setLibrary(SPRING_BOOT);

-        CliOption cliOpt = new CliOption(CodegenConstants.LIBRARY, "library template (sub-template) to use");
+        CliOption cliOpt = new CliOption(CodegenConstants.LIBRARY, CodegenConstants.LIBRARY_DESC);
        cliOpt.setDefault(SPRING_BOOT);
        cliOpt.setEnum(supportedLibraries);
        cliOptions.add(cliOpt);
--- a/modules/openapi-generator/src/main/resources/kotlin-client/README.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/README.mustache
@ -2,7 +2,7 @@

 ## Requires

-* Kotlin 1.3.20
+* Kotlin 1.3.31
 * Gradle 4.9

 ## Build
--- a/modules/openapi-generator/src/main/resources/kotlin-client/api.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/api.mustache
@ -4,7 +4,17 @@ package {{apiPackage}}
 {{#imports}}import {{import}}
 {{/imports}}

-import {{packageName}}.infrastructure.*
+import {{packageName}}.infrastructure.ApiClient
+import {{packageName}}.infrastructure.ClientException
+import {{packageName}}.infrastructure.ClientError
+import {{packageName}}.infrastructure.ServerException
+import {{packageName}}.infrastructure.ServerError
+import {{packageName}}.infrastructure.MultiValueMap
+import {{packageName}}.infrastructure.RequestConfig
+import {{packageName}}.infrastructure.RequestMethod
+import {{packageName}}.infrastructure.ResponseType
+import {{packageName}}.infrastructure.Success
+import {{packageName}}.infrastructure.toMultiValue
 {{#threetenbp}}
 import org.threeten.bp.LocalDateTime
 {{/threetenbp}}
@ -23,7 +33,7 @@ class {{classname}}(basePath: kotlin.String = "{{{basePath}}}") : ApiClient(base
    fun {{operationId}}({{#allParams}}{{paramName}}: {{{dataType}}}{{^required}}?{{/required}}{{#hasMore}}, {{/hasMore}}{{/allParams}}) : {{#returnType}}{{{returnType}}}{{/returnType}}{{^returnType}}Unit{{/returnType}} {
        val localVariableBody: kotlin.Any? = {{#hasBodyParam}}{{#bodyParams}}{{paramName}}{{/bodyParams}}{{/hasBodyParam}}{{^hasBodyParam}}{{^hasFormParams}}null{{/hasFormParams}}{{#hasFormParams}}mapOf({{#formParams}}"{{{baseName}}}" to "${{paramName}}"{{#hasMore}}, {{/hasMore}}{{/formParams}}){{/hasFormParams}}{{/hasBodyParam}}
        val localVariableQuery: MultiValueMap = {{^hasQueryParams}}mapOf(){{/hasQueryParams}}{{#hasQueryParams}}mapOf({{#queryParams}}"{{paramName}}" to {{#isContainer}}toMultiValue({{paramName}}.toList(), "{{collectionFormat}}"){{/isContainer}}{{^isContainer}}listOf("${{paramName}}"){{/isContainer}}{{#hasMore}}, {{/hasMore}}{{/queryParams}}){{/hasQueryParams}}
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf({{#hasFormParams}}"Content-Type" to "multipart/form-data"{{/hasFormParams}}{{^hasHeaderParams}}){{/hasHeaderParams}}{{#hasHeaderParams}}{{#hasFormParams}}, {{/hasFormParams}}{{#headerParams}}"{{baseName}}" to {{#isContainer}}{{paramName}}.joinToString(separator = collectionDelimiter("{{collectionFormat}}")){{/isContainer}}{{^isContainer}}{{paramName}}.toString(){{/isContainer}}{{#hasMore}}, {{/hasMore}}{{/headerParams}}){{/hasHeaderParams}}
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf({{#hasFormParams}}"Content-Type" to {{^consumes}}"multipart/form-data"{{/consumes}}{{#consumes.0}}"{{MediaType}}"{{/consumes.0}}{{/hasFormParams}}{{^hasHeaderParams}}){{/hasHeaderParams}}{{#hasHeaderParams}}{{#hasFormParams}}, {{/hasFormParams}}{{#headerParams}}"{{baseName}}" to {{#isContainer}}{{paramName}}.joinToString(separator = collectionDelimiter("{{collectionFormat}}")){{/isContainer}}{{^isContainer}}{{paramName}}.toString(){{/isContainer}}{{#hasMore}}, {{/hasMore}}{{/headerParams}}){{/hasHeaderParams}}
        val localVariableConfig = RequestConfig(
            RequestMethod.{{httpMethod}},
            "{{path}}"{{#pathParams}}.replace("{"+"{{baseName}}"+"}", "${{paramName}}"){{/pathParams}},
--- a/modules/openapi-generator/src/main/resources/kotlin-client/build.gradle.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/build.gradle.mustache
@ -7,7 +7,7 @@ wrapper {
 }

 buildscript {
-    ext.kotlin_version = '1.3.20'
+    ext.kotlin_version = '1.3.31'

    repositories {
        mavenCentral()
@ -32,7 +32,7 @@ dependencies {
    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
    compile "com.squareup.moshi:moshi-kotlin:1.5.0"
    compile "com.squareup.moshi:moshi-adapters:1.5.0"
-    compile "com.squareup.okhttp3:okhttp:3.8.0"
-    compile "org.threeten:threetenbp:1.3.6"
+    compile "com.squareup.okhttp3:okhttp:3.14.0"
+    compile "org.threeten:threetenbp:1.3.8"
    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.1.0"
 }
--- a/modules/openapi-generator/src/main/resources/kotlin-client/infrastructure/ApiClient.kt.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/infrastructure/ApiClient.kt.mustache
@ -3,9 +3,15 @@ package {{packageName}}.infrastructure
 import com.squareup.moshi.FromJson
 import com.squareup.moshi.Moshi
 import com.squareup.moshi.ToJson
-import okhttp3.*
+import okhttp3.OkHttpClient
+import okhttp3.RequestBody
+import okhttp3.MediaType
+import okhttp3.FormBody
+import okhttp3.HttpUrl
+import okhttp3.ResponseBody
+import okhttp3.Request
 import java.io.File
-import java.util.*
+import java.util.UUID

 open class ApiClient(val baseUrl: String) {
    companion object {
@ -13,6 +19,7 @@ open class ApiClient(val baseUrl: String) {
        protected const val Accept = "Accept"
        protected const val JsonMediaType = "application/json"
        protected const val FormDataMediaType = "multipart/form-data"
+        protected const val FormUrlEncMediaType = "application/x-www-form-urlencoded"
        protected const val XmlMediaType = "application/xml"

        @JvmStatic
@ -22,12 +29,6 @@ open class ApiClient(val baseUrl: String) {

        @JvmStatic
        val builder: OkHttpClient.Builder = OkHttpClient.Builder()
-
-        @JvmStatic
-        var defaultHeaders: Map<String, String> by ApplicationDelegates.setOnce(mapOf(ContentType to JsonMediaType, Accept to JsonMediaType))
-
-        @JvmStatic
-        val jsonHeaders: Map<String, String> = mapOf(ContentType to JsonMediaType, Accept to JsonMediaType)
    }

    protected inline fun <reified T> requestBody(content: T, mediaType: String = JsonMediaType): RequestBody =
@ -35,7 +36,7 @@ open class ApiClient(val baseUrl: String) {
            content is File -> RequestBody.create(
                MediaType.parse(mediaType), content
            )
-             mediaType == FormDataMediaType -> {
+            mediaType == FormDataMediaType || mediaType == FormUrlEncMediaType -> {
                var builder = FormBody.Builder()
                // content's type *must* be Map<String, Any>
                @Suppress("UNCHECKED_CAST")
@ -52,8 +53,14 @@ open class ApiClient(val baseUrl: String) {
            else -> TODO("requestBody currently only supports JSON body and File body.")
        }

-    protected inline fun <reified T: Any?> responseBody(body: ResponseBody?, mediaType: String = JsonMediaType): T? {
-        if(body == null) return null
+    protected inline fun <reified T: Any?> responseBody(body: ResponseBody?, mediaType: String? = JsonMediaType): T? {
+        if(body == null) {
+            return null
+        }
+        val bodyContent = body.string()
+        if (bodyContent.length == 0) {
+            return null
+        }
        return when(mediaType) {
            JsonMediaType -> Moshi.Builder().add(object {
                    @ToJson
@ -62,8 +69,8 @@ open class ApiClient(val baseUrl: String) {
                    fun fromJson(s: String) = UUID.fromString(s)
                })
                .add(ByteArrayAdapter())
-                .build().adapter(T::class.java).fromJson(body.source())
-            else -> TODO()
+                .build().adapter(T::class.java).fromJson(bodyContent)
+            else ->  TODO("responseBody currently only supports JSON body.")
        }
    }

@ -80,7 +87,15 @@ open class ApiClient(val baseUrl: String) {
        }

        val url = urlBuilder.build()
-        val headers = requestConfig.headers + defaultHeaders
+
+        // take content-type/accept from spec or set to default (application/json) if not defined
+        if (requestConfig.headers[ContentType].isNullOrEmpty()) {
+            requestConfig.headers.put(ContentType, JsonMediaType)
+        }
+        if (requestConfig.headers[Accept].isNullOrEmpty()) {
+            requestConfig.headers.put(Accept, JsonMediaType)
+        }
+        val headers = requestConfig.headers

        if(headers[ContentType] ?: "" == "") {
            throw kotlin.IllegalStateException("Missing Content-Type header. This is required.")
@ -90,9 +105,8 @@ open class ApiClient(val baseUrl: String) {
            throw kotlin.IllegalStateException("Missing Accept header. This is required.")
        }

-        // TODO: support multiple contentType,accept options here.
+        // TODO: support multiple contentType options here.
        val contentType = (headers[ContentType] as String).substringBefore(";").toLowerCase()
-        val accept = (headers[Accept] as String).substringBefore(";").toLowerCase()

        var request : Request.Builder =  when (requestConfig.method) {
            RequestMethod.DELETE -> Request.Builder().url(url).delete()
@ -108,6 +122,7 @@ open class ApiClient(val baseUrl: String) {

        val realRequest = request.build()
        val response = client.newCall(realRequest).execute()
+        val accept = response.header(ContentType)?.substringBefore(";")?.toLowerCase()

        // TODO: handle specific mapping types. e.g. Map<int, Class<?>>
        when {
--- a/modules/openapi-generator/src/main/resources/kotlin-client/infrastructure/RequestConfig.kt.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/infrastructure/RequestConfig.kt.mustache
@ -11,6 +11,6 @@ package {{packageName}}.infrastructure
 data class RequestConfig(
    val method: RequestMethod,
    val path: String,
-    val headers: Map<String, String> = mapOf(),
+    val headers: MutableMap<String, String> = mutableMapOf(),
    val query: Map<String, List<String>> = mapOf()
 )
--- a/modules/openapi-generator/src/main/resources/kotlin-server/libraries/ktor/ApiKeyAuth.kt.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-server/libraries/ktor/ApiKeyAuth.kt.mustache
@ -2,8 +2,15 @@ package {{packageName}}.infrastructure

 import io.ktor.application.ApplicationCall
 import io.ktor.application.call
-import io.ktor.auth.*
-import io.ktor.http.auth.*
+import io.ktor.auth.Authentication
+import io.ktor.auth.AuthenticationFailedCause
+import io.ktor.auth.AuthenticationPipeline
+import io.ktor.auth.AuthenticationProvider
+import io.ktor.auth.Credential
+import io.ktor.auth.Principal
+import io.ktor.auth.UnauthorizedResponse
+import io.ktor.http.auth.HeaderValueEncoding
+import io.ktor.http.auth.HttpAuthHeader
 import io.ktor.request.ApplicationRequest
 import io.ktor.response.respond

--- a/modules/openapi-generator/src/main/resources/kotlin-server/libraries/ktor/AppMain.kt.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-server/libraries/ktor/AppMain.kt.mustache
@ -1,29 +1,36 @@
 package {{packageName}}

-import com.codahale.metrics.*
+import com.codahale.metrics.Slf4jReporter
 import com.typesafe.config.ConfigFactory
-import io.ktor.application.*
+import io.ktor.application.Application
+import io.ktor.application.ApplicationStopping
+import io.ktor.application.install
+import io.ktor.application.log
 import io.ktor.client.HttpClient
 import io.ktor.client.engine.apache.Apache
 import io.ktor.config.HoconApplicationConfig
-import io.ktor.features.*
+import io.ktor.features.AutoHeadResponse
+import io.ktor.features.Compression
+import io.ktor.features.ContentNegotiation
+import io.ktor.features.DefaultHeaders
+import io.ktor.features.HSTS
 import io.ktor.gson.GsonConverter
 import io.ktor.http.ContentType
-import io.ktor.locations.*
-import io.ktor.metrics.*
-import io.ktor.routing.*
-import java.util.concurrent.*
+import io.ktor.locations.KtorExperimentalLocationsAPI
+import io.ktor.locations.Locations
+import io.ktor.metrics.Metrics
+import io.ktor.routing.Routing
+import java.util.concurrent.TimeUnit
 {{#hasAuthMethods}}
-import io.ktor.auth.*
+import io.ktor.auth.Authentication
+import io.ktor.auth.oauth
 import io.ktor.util.KtorExperimentalAPI
-import org.openapitools.server.infrastructure.*
+import org.openapitools.server.infrastructure.ApiKeyCredential
+import org.openapitools.server.infrastructure.ApiPrincipal
+import org.openapitools.server.infrastructure.apiKeyAuth
 {{/hasAuthMethods}}
-{{#generateApis}}
-import {{apiPackage}}.*
-{{/generateApis}}
-
-{{#imports}}import {{import}}
-{{/imports}}
+{{#generateApis}}{{#apiInfo}}{{#apis}}import {{apiPackage}}.{{classname}}
+{{/apis}}{{/apiInfo}}{{/generateApis}}

@KtorExperimentalAPI
 internal val settings = HoconApplicationConfig(ConfigFactory.defaultApplication(HTTP::class.java.classLoader))
--- a/modules/openapi-generator/src/main/resources/kotlin-server/libraries/ktor/Configuration.kt.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-server/libraries/ktor/Configuration.kt.mustache
@ -2,8 +2,12 @@ package {{packageName}}

 // Use this file to hold package-level internal functions that return receiver object passed to the `install` method.
 import io.ktor.auth.OAuthServerSettings
-import io.ktor.features.*
-import io.ktor.http.*
+import io.ktor.features.Compression
+import io.ktor.features.HSTS
+import io.ktor.features.deflate
+import io.ktor.features.gzip
+import io.ktor.features.minimumSize
+import io.ktor.http.HttpMethod
 import io.ktor.util.KtorExperimentalAPI
 import java.time.Duration
 import java.util.concurrent.Executors
--- a/modules/openapi-generator/src/main/resources/kotlin-server/libraries/ktor/Paths.kt.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-server/libraries/ktor/Paths.kt.mustache
@ -1,11 +1,9 @@
 {{>licenseInfo}}
 package {{packageName}}

-import io.ktor.locations.*
-import {{modelPackage}}.*
-
-{{#imports}}
-import {{import}}
+import io.ktor.locations.KtorExperimentalLocationsAPI
+import io.ktor.locations.Location
+{{#imports}}import {{import}}
 {{/imports}}

 {{#apiInfo}}
--- a/modules/openapi-generator/src/main/resources/kotlin-server/libraries/ktor/api.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-server/libraries/ktor/api.mustache
@ -10,10 +10,15 @@ import io.ktor.auth.OAuthAccessTokenResponse
 import io.ktor.auth.OAuthServerSettings
 import io.ktor.http.ContentType
 import io.ktor.http.HttpStatusCode
-import io.ktor.locations.*
+import io.ktor.locations.KtorExperimentalLocationsAPI
+import io.ktor.locations.delete
+import io.ktor.locations.get
 import io.ktor.response.respond
 import io.ktor.response.respondText
-import io.ktor.routing.*
+import io.ktor.routing.Route
+import io.ktor.routing.post
+import io.ktor.routing.put
+import io.ktor.routing.route

 import {{packageName}}.Paths
 import {{packageName}}.infrastructure.ApiPrincipal
--- a/modules/openapi-generator/src/main/resources/kotlin-spring/api.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-spring/api.mustache
@ -3,7 +3,13 @@ package {{package}}
 {{#imports}}import {{import}}
 {{/imports}}
 {{#swaggerAnnotations}}
-import io.swagger.annotations.*
+import io.swagger.annotations.Api
+import io.swagger.annotations.ApiOperation
+import io.swagger.annotations.ApiParam
+import io.swagger.annotations.ApiResponse
+import io.swagger.annotations.ApiResponses
+import io.swagger.annotations.Authorization
+import io.swagger.annotations.AuthorizationScope
 {{/swaggerAnnotations}}
 import org.springframework.http.HttpStatus
 import org.springframework.http.MediaType
@ -24,7 +30,13 @@ import org.springframework.beans.factory.annotation.Autowired

 {{#useBeanValidation}}
 import javax.validation.Valid
-import javax.validation.constraints.*
+import javax.validation.constraints.DecimalMax
+import javax.validation.constraints.DecimalMin
+import javax.validation.constraints.Max
+import javax.validation.constraints.Min
+import javax.validation.constraints.NotNull
+import javax.validation.constraints.Pattern
+import javax.validation.constraints.Size
 {{/useBeanValidation}}

 import kotlin.collections.List
--- a/modules/openapi-generator/src/main/resources/kotlin-spring/model.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-spring/model.mustache
@ -4,8 +4,13 @@ import java.util.Objects
 {{#imports}}import {{import}}
 {{/imports}}
 {{#useBeanValidation}}
-import javax.validation.Valid
-import javax.validation.constraints.*
+import javax.validation.constraints.DecimalMax
+import javax.validation.constraints.DecimalMin
+import javax.validation.constraints.Max
+import javax.validation.constraints.Min
+import javax.validation.constraints.NotNull
+import javax.validation.constraints.Pattern
+import javax.validation.constraints.Size
 {{/useBeanValidation}}
 {{#swaggerAnnotations}}
 import io.swagger.annotations.ApiModelProperty
--- a/samples/client/petstore/kotlin-string/README.md
+++ b/samples/client/petstore/kotlin-string/README.md
@ -2,7 +2,7 @@

 ## Requires

-* Kotlin 1.3.20
+* Kotlin 1.3.31
 * Gradle 4.9

 ## Build
--- a/samples/client/petstore/kotlin-string/build.gradle
+++ b/samples/client/petstore/kotlin-string/build.gradle
@ -7,7 +7,7 @@ wrapper {
 }

 buildscript {
-    ext.kotlin_version = '1.3.20'
+    ext.kotlin_version = '1.3.31'

    repositories {
        mavenCentral()
@ -32,7 +32,7 @@ dependencies {
    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
    compile "com.squareup.moshi:moshi-kotlin:1.5.0"
    compile "com.squareup.moshi:moshi-adapters:1.5.0"
-    compile "com.squareup.okhttp3:okhttp:3.8.0"
-    compile "org.threeten:threetenbp:1.3.6"
+    compile "com.squareup.okhttp3:okhttp:3.14.0"
+    compile "org.threeten:threetenbp:1.3.8"
    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.1.0"
 }
--- a/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
+++ b/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
@ -14,7 +14,17 @@ package org.openapitools.client.apis
 import org.openapitools.client.models.ApiResponse
 import org.openapitools.client.models.Pet

-import org.openapitools.client.infrastructure.*
+import org.openapitools.client.infrastructure.ApiClient
+import org.openapitools.client.infrastructure.ClientException
+import org.openapitools.client.infrastructure.ClientError
+import org.openapitools.client.infrastructure.ServerException
+import org.openapitools.client.infrastructure.ServerError
+import org.openapitools.client.infrastructure.MultiValueMap
+import org.openapitools.client.infrastructure.RequestConfig
+import org.openapitools.client.infrastructure.RequestMethod
+import org.openapitools.client.infrastructure.ResponseType
+import org.openapitools.client.infrastructure.Success
+import org.openapitools.client.infrastructure.toMultiValue

 class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiClient(basePath) {

@ -27,7 +37,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun addPet(body: Pet) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/pet",
@ -58,7 +68,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun deletePet(petId: kotlin.Long, apiKey: kotlin.String?) : Unit {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf("api_key" to apiKey.toString())
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf("api_key" to apiKey.toString())
        val localVariableConfig = RequestConfig(
            RequestMethod.DELETE,
            "/pet/{petId}".replace("{"+"petId"+"}", "$petId"),
@ -89,7 +99,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun findPetsByStatus(status: kotlin.Array<kotlin.String>) : kotlin.Array<Pet> {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf("status" to toMultiValue(status.toList(), "csv"))
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/pet/findByStatus",
@ -120,7 +130,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun findPetsByTags(tags: kotlin.Array<kotlin.String>) : kotlin.Array<Pet> {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf("tags" to toMultiValue(tags.toList(), "csv"))
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/pet/findByTags",
@ -151,7 +161,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun getPetById(petId: kotlin.Long) : Pet {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/pet/{petId}".replace("{"+"petId"+"}", "$petId"),
@ -181,7 +191,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun updatePet(body: Pet) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.PUT,
            "/pet",
@ -213,7 +223,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun updatePetWithForm(petId: kotlin.Long, name: kotlin.String?, status: kotlin.String?) : Unit {
        val localVariableBody: kotlin.Any? = mapOf("name" to "$name", "status" to "$status")
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf("Content-Type" to "multipart/form-data")
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf("Content-Type" to "")
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/pet/{petId}".replace("{"+"petId"+"}", "$petId"),
@ -246,7 +256,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun uploadFile(petId: kotlin.Long, additionalMetadata: kotlin.String?, file: java.io.File?) : ApiResponse {
        val localVariableBody: kotlin.Any? = mapOf("additionalMetadata" to "$additionalMetadata", "file" to "$file")
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf("Content-Type" to "multipart/form-data")
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf("Content-Type" to "")
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/pet/{petId}/uploadImage".replace("{"+"petId"+"}", "$petId"),
--- a/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
+++ b/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
@ -13,7 +13,17 @@ package org.openapitools.client.apis

 import org.openapitools.client.models.Order

-import org.openapitools.client.infrastructure.*
+import org.openapitools.client.infrastructure.ApiClient
+import org.openapitools.client.infrastructure.ClientException
+import org.openapitools.client.infrastructure.ClientError
+import org.openapitools.client.infrastructure.ServerException
+import org.openapitools.client.infrastructure.ServerError
+import org.openapitools.client.infrastructure.MultiValueMap
+import org.openapitools.client.infrastructure.RequestConfig
+import org.openapitools.client.infrastructure.RequestMethod
+import org.openapitools.client.infrastructure.ResponseType
+import org.openapitools.client.infrastructure.Success
+import org.openapitools.client.infrastructure.toMultiValue

 class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiClient(basePath) {

@ -26,7 +36,7 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
    fun deleteOrder(orderId: kotlin.String) : Unit {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.DELETE,
            "/store/order/{orderId}".replace("{"+"orderId"+"}", "$orderId"),
@ -56,7 +66,7 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
    fun getInventory() : kotlin.collections.Map<kotlin.String, kotlin.Int> {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/store/inventory",
@ -87,7 +97,7 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
    fun getOrderById(orderId: kotlin.Long) : Order {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/store/order/{orderId}".replace("{"+"orderId"+"}", "$orderId"),
@ -118,7 +128,7 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
    fun placeOrder(body: Order) : Order {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/store/order",
--- a/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
+++ b/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
@ -13,7 +13,17 @@ package org.openapitools.client.apis

 import org.openapitools.client.models.User

-import org.openapitools.client.infrastructure.*
+import org.openapitools.client.infrastructure.ApiClient
+import org.openapitools.client.infrastructure.ClientException
+import org.openapitools.client.infrastructure.ClientError
+import org.openapitools.client.infrastructure.ServerException
+import org.openapitools.client.infrastructure.ServerError
+import org.openapitools.client.infrastructure.MultiValueMap
+import org.openapitools.client.infrastructure.RequestConfig
+import org.openapitools.client.infrastructure.RequestMethod
+import org.openapitools.client.infrastructure.ResponseType
+import org.openapitools.client.infrastructure.Success
+import org.openapitools.client.infrastructure.toMultiValue

 class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiClient(basePath) {

@ -26,7 +36,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun createUser(body: User) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/user",
@ -56,7 +66,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun createUsersWithArrayInput(body: kotlin.Array<User>) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/user/createWithArray",
@ -86,7 +96,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun createUsersWithListInput(body: kotlin.Array<User>) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/user/createWithList",
@ -116,7 +126,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun deleteUser(username: kotlin.String) : Unit {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.DELETE,
            "/user/{username}".replace("{"+"username"+"}", "$username"),
@ -147,7 +157,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun getUserByName(username: kotlin.String) : User {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/user/{username}".replace("{"+"username"+"}", "$username"),
@ -179,7 +189,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun loginUser(username: kotlin.String, password: kotlin.String) : kotlin.String {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf("username" to listOf("$username"), "password" to listOf("$password"))
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/user/login",
@ -208,7 +218,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun logoutUser() : Unit {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/user/logout",
@ -239,7 +249,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun updateUser(username: kotlin.String, body: User) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.PUT,
            "/user/{username}".replace("{"+"username"+"}", "$username"),
--- a/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
+++ b/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
@ -3,9 +3,15 @@ package org.openapitools.client.infrastructure
 import com.squareup.moshi.FromJson
 import com.squareup.moshi.Moshi
 import com.squareup.moshi.ToJson
-import okhttp3.*
+import okhttp3.OkHttpClient
+import okhttp3.RequestBody
+import okhttp3.MediaType
+import okhttp3.FormBody
+import okhttp3.HttpUrl
+import okhttp3.ResponseBody
+import okhttp3.Request
 import java.io.File
-import java.util.*
+import java.util.UUID

 open class ApiClient(val baseUrl: String) {
    companion object {
@ -13,6 +19,7 @@ open class ApiClient(val baseUrl: String) {
        protected const val Accept = "Accept"
        protected const val JsonMediaType = "application/json"
        protected const val FormDataMediaType = "multipart/form-data"
+        protected const val FormUrlEncMediaType = "application/x-www-form-urlencoded"
        protected const val XmlMediaType = "application/xml"

        @JvmStatic
@ -22,12 +29,6 @@ open class ApiClient(val baseUrl: String) {

        @JvmStatic
        val builder: OkHttpClient.Builder = OkHttpClient.Builder()
-
-        @JvmStatic
-        var defaultHeaders: Map<String, String> by ApplicationDelegates.setOnce(mapOf(ContentType to JsonMediaType, Accept to JsonMediaType))
-
-        @JvmStatic
-        val jsonHeaders: Map<String, String> = mapOf(ContentType to JsonMediaType, Accept to JsonMediaType)
    }

    protected inline fun <reified T> requestBody(content: T, mediaType: String = JsonMediaType): RequestBody =
@ -35,7 +36,7 @@ open class ApiClient(val baseUrl: String) {
            content is File -> RequestBody.create(
                MediaType.parse(mediaType), content
            )
-             mediaType == FormDataMediaType -> {
+            mediaType == FormDataMediaType || mediaType == FormUrlEncMediaType -> {
                var builder = FormBody.Builder()
                // content's type *must* be Map<String, Any>
                @Suppress("UNCHECKED_CAST")
@ -52,8 +53,14 @@ open class ApiClient(val baseUrl: String) {
            else -> TODO("requestBody currently only supports JSON body and File body.")
        }

-    protected inline fun <reified T: Any?> responseBody(body: ResponseBody?, mediaType: String = JsonMediaType): T? {
-        if(body == null) return null
+    protected inline fun <reified T: Any?> responseBody(body: ResponseBody?, mediaType: String? = JsonMediaType): T? {
+        if(body == null) {
+            return null
+        }
+        val bodyContent = body.string()
+        if (bodyContent.length == 0) {
+            return null
+        }
        return when(mediaType) {
            JsonMediaType -> Moshi.Builder().add(object {
                    @ToJson
@ -62,8 +69,8 @@ open class ApiClient(val baseUrl: String) {
                    fun fromJson(s: String) = UUID.fromString(s)
                })
                .add(ByteArrayAdapter())
-                .build().adapter(T::class.java).fromJson(body.source())
-            else -> TODO()
+                .build().adapter(T::class.java).fromJson(bodyContent)
+            else ->  TODO("responseBody currently only supports JSON body.")
        }
    }

@ -80,7 +87,15 @@ open class ApiClient(val baseUrl: String) {
        }

        val url = urlBuilder.build()
-        val headers = requestConfig.headers + defaultHeaders
+
+        // take content-type/accept from spec or set to default (application/json) if not defined
+        if (requestConfig.headers[ContentType].isNullOrEmpty()) {
+            requestConfig.headers.put(ContentType, JsonMediaType)
+        }
+        if (requestConfig.headers[Accept].isNullOrEmpty()) {
+            requestConfig.headers.put(Accept, JsonMediaType)
+        }
+        val headers = requestConfig.headers

        if(headers[ContentType] ?: "" == "") {
            throw kotlin.IllegalStateException("Missing Content-Type header. This is required.")
@ -90,9 +105,8 @@ open class ApiClient(val baseUrl: String) {
            throw kotlin.IllegalStateException("Missing Accept header. This is required.")
        }

-        // TODO: support multiple contentType,accept options here.
+        // TODO: support multiple contentType options here.
        val contentType = (headers[ContentType] as String).substringBefore(";").toLowerCase()
-        val accept = (headers[Accept] as String).substringBefore(";").toLowerCase()

        var request : Request.Builder =  when (requestConfig.method) {
            RequestMethod.DELETE -> Request.Builder().url(url).delete()
@ -108,6 +122,7 @@ open class ApiClient(val baseUrl: String) {

        val realRequest = request.build()
        val response = client.newCall(realRequest).execute()
+        val accept = response.header(ContentType)?.substringBefore(";")?.toLowerCase()

        // TODO: handle specific mapping types. e.g. Map<int, Class<?>>
        when {
--- a/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/infrastructure/RequestConfig.kt
+++ b/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/infrastructure/RequestConfig.kt
@ -11,6 +11,6 @@ package org.openapitools.client.infrastructure
 data class RequestConfig(
    val method: RequestMethod,
    val path: String,
-    val headers: Map<String, String> = mapOf(),
+    val headers: MutableMap<String, String> = mutableMapOf(),
    val query: Map<String, List<String>> = mapOf()
 )
--- a/samples/client/petstore/kotlin-threetenbp/README.md
+++ b/samples/client/petstore/kotlin-threetenbp/README.md
@ -2,7 +2,7 @@

 ## Requires

-* Kotlin 1.3.20
+* Kotlin 1.3.31
 * Gradle 4.9

 ## Build
--- a/samples/client/petstore/kotlin-threetenbp/build.gradle
+++ b/samples/client/petstore/kotlin-threetenbp/build.gradle
@ -7,7 +7,7 @@ wrapper {
 }

 buildscript {
-    ext.kotlin_version = '1.3.20'
+    ext.kotlin_version = '1.3.31'

    repositories {
        mavenCentral()
@ -32,7 +32,7 @@ dependencies {
    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
    compile "com.squareup.moshi:moshi-kotlin:1.5.0"
    compile "com.squareup.moshi:moshi-adapters:1.5.0"
-    compile "com.squareup.okhttp3:okhttp:3.8.0"
-    compile "org.threeten:threetenbp:1.3.6"
+    compile "com.squareup.okhttp3:okhttp:3.14.0"
+    compile "org.threeten:threetenbp:1.3.8"
    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.1.0"
 }
--- a/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
+++ b/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
@ -14,7 +14,17 @@ package org.openapitools.client.apis
 import org.openapitools.client.models.ApiResponse
 import org.openapitools.client.models.Pet

-import org.openapitools.client.infrastructure.*
+import org.openapitools.client.infrastructure.ApiClient
+import org.openapitools.client.infrastructure.ClientException
+import org.openapitools.client.infrastructure.ClientError
+import org.openapitools.client.infrastructure.ServerException
+import org.openapitools.client.infrastructure.ServerError
+import org.openapitools.client.infrastructure.MultiValueMap
+import org.openapitools.client.infrastructure.RequestConfig
+import org.openapitools.client.infrastructure.RequestMethod
+import org.openapitools.client.infrastructure.ResponseType
+import org.openapitools.client.infrastructure.Success
+import org.openapitools.client.infrastructure.toMultiValue
 import org.threeten.bp.LocalDateTime

 class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiClient(basePath) {
@ -28,7 +38,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun addPet(body: Pet) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/pet",
@ -59,7 +69,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun deletePet(petId: kotlin.Long, apiKey: kotlin.String?) : Unit {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf("api_key" to apiKey.toString())
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf("api_key" to apiKey.toString())
        val localVariableConfig = RequestConfig(
            RequestMethod.DELETE,
            "/pet/{petId}".replace("{"+"petId"+"}", "$petId"),
@ -90,7 +100,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun findPetsByStatus(status: kotlin.Array<kotlin.String>) : kotlin.Array<Pet> {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf("status" to toMultiValue(status.toList(), "csv"))
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/pet/findByStatus",
@ -121,7 +131,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun findPetsByTags(tags: kotlin.Array<kotlin.String>) : kotlin.Array<Pet> {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf("tags" to toMultiValue(tags.toList(), "csv"))
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/pet/findByTags",
@ -152,7 +162,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun getPetById(petId: kotlin.Long) : Pet {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/pet/{petId}".replace("{"+"petId"+"}", "$petId"),
@ -182,7 +192,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun updatePet(body: Pet) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.PUT,
            "/pet",
@ -214,7 +224,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun updatePetWithForm(petId: kotlin.Long, name: kotlin.String?, status: kotlin.String?) : Unit {
        val localVariableBody: kotlin.Any? = mapOf("name" to "$name", "status" to "$status")
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf("Content-Type" to "multipart/form-data")
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf("Content-Type" to "")
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/pet/{petId}".replace("{"+"petId"+"}", "$petId"),
@ -247,7 +257,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun uploadFile(petId: kotlin.Long, additionalMetadata: kotlin.String?, file: java.io.File?) : ApiResponse {
        val localVariableBody: kotlin.Any? = mapOf("additionalMetadata" to "$additionalMetadata", "file" to "$file")
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf("Content-Type" to "multipart/form-data")
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf("Content-Type" to "")
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/pet/{petId}/uploadImage".replace("{"+"petId"+"}", "$petId"),
--- a/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
+++ b/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
@ -13,7 +13,17 @@ package org.openapitools.client.apis

 import org.openapitools.client.models.Order

-import org.openapitools.client.infrastructure.*
+import org.openapitools.client.infrastructure.ApiClient
+import org.openapitools.client.infrastructure.ClientException
+import org.openapitools.client.infrastructure.ClientError
+import org.openapitools.client.infrastructure.ServerException
+import org.openapitools.client.infrastructure.ServerError
+import org.openapitools.client.infrastructure.MultiValueMap
+import org.openapitools.client.infrastructure.RequestConfig
+import org.openapitools.client.infrastructure.RequestMethod
+import org.openapitools.client.infrastructure.ResponseType
+import org.openapitools.client.infrastructure.Success
+import org.openapitools.client.infrastructure.toMultiValue
 import org.threeten.bp.LocalDateTime

 class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiClient(basePath) {
@ -27,7 +37,7 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
    fun deleteOrder(orderId: kotlin.String) : Unit {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.DELETE,
            "/store/order/{orderId}".replace("{"+"orderId"+"}", "$orderId"),
@ -57,7 +67,7 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
    fun getInventory() : kotlin.collections.Map<kotlin.String, kotlin.Int> {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/store/inventory",
@ -88,7 +98,7 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
    fun getOrderById(orderId: kotlin.Long) : Order {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/store/order/{orderId}".replace("{"+"orderId"+"}", "$orderId"),
@ -119,7 +129,7 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
    fun placeOrder(body: Order) : Order {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/store/order",
--- a/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
+++ b/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
@ -13,7 +13,17 @@ package org.openapitools.client.apis

 import org.openapitools.client.models.User

-import org.openapitools.client.infrastructure.*
+import org.openapitools.client.infrastructure.ApiClient
+import org.openapitools.client.infrastructure.ClientException
+import org.openapitools.client.infrastructure.ClientError
+import org.openapitools.client.infrastructure.ServerException
+import org.openapitools.client.infrastructure.ServerError
+import org.openapitools.client.infrastructure.MultiValueMap
+import org.openapitools.client.infrastructure.RequestConfig
+import org.openapitools.client.infrastructure.RequestMethod
+import org.openapitools.client.infrastructure.ResponseType
+import org.openapitools.client.infrastructure.Success
+import org.openapitools.client.infrastructure.toMultiValue
 import org.threeten.bp.LocalDateTime

 class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiClient(basePath) {
@ -27,7 +37,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun createUser(body: User) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/user",
@ -57,7 +67,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun createUsersWithArrayInput(body: kotlin.Array<User>) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/user/createWithArray",
@ -87,7 +97,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun createUsersWithListInput(body: kotlin.Array<User>) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/user/createWithList",
@ -117,7 +127,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun deleteUser(username: kotlin.String) : Unit {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.DELETE,
            "/user/{username}".replace("{"+"username"+"}", "$username"),
@ -148,7 +158,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun getUserByName(username: kotlin.String) : User {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/user/{username}".replace("{"+"username"+"}", "$username"),
@ -180,7 +190,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun loginUser(username: kotlin.String, password: kotlin.String) : kotlin.String {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf("username" to listOf("$username"), "password" to listOf("$password"))
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/user/login",
@ -209,7 +219,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun logoutUser() : Unit {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/user/logout",
@ -240,7 +250,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun updateUser(username: kotlin.String, body: User) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.PUT,
            "/user/{username}".replace("{"+"username"+"}", "$username"),
--- a/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
+++ b/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
@ -3,9 +3,15 @@ package org.openapitools.client.infrastructure
 import com.squareup.moshi.FromJson
 import com.squareup.moshi.Moshi
 import com.squareup.moshi.ToJson
-import okhttp3.*
+import okhttp3.OkHttpClient
+import okhttp3.RequestBody
+import okhttp3.MediaType
+import okhttp3.FormBody
+import okhttp3.HttpUrl
+import okhttp3.ResponseBody
+import okhttp3.Request
 import java.io.File
-import java.util.*
+import java.util.UUID

 open class ApiClient(val baseUrl: String) {
    companion object {
@ -13,6 +19,7 @@ open class ApiClient(val baseUrl: String) {
        protected const val Accept = "Accept"
        protected const val JsonMediaType = "application/json"
        protected const val FormDataMediaType = "multipart/form-data"
+        protected const val FormUrlEncMediaType = "application/x-www-form-urlencoded"
        protected const val XmlMediaType = "application/xml"

        @JvmStatic
@ -22,12 +29,6 @@ open class ApiClient(val baseUrl: String) {

        @JvmStatic
        val builder: OkHttpClient.Builder = OkHttpClient.Builder()
-
-        @JvmStatic
-        var defaultHeaders: Map<String, String> by ApplicationDelegates.setOnce(mapOf(ContentType to JsonMediaType, Accept to JsonMediaType))
-
-        @JvmStatic
-        val jsonHeaders: Map<String, String> = mapOf(ContentType to JsonMediaType, Accept to JsonMediaType)
    }

    protected inline fun <reified T> requestBody(content: T, mediaType: String = JsonMediaType): RequestBody =
@ -35,7 +36,7 @@ open class ApiClient(val baseUrl: String) {
            content is File -> RequestBody.create(
                MediaType.parse(mediaType), content
            )
-             mediaType == FormDataMediaType -> {
+            mediaType == FormDataMediaType || mediaType == FormUrlEncMediaType -> {
                var builder = FormBody.Builder()
                // content's type *must* be Map<String, Any>
                @Suppress("UNCHECKED_CAST")
@ -52,8 +53,14 @@ open class ApiClient(val baseUrl: String) {
            else -> TODO("requestBody currently only supports JSON body and File body.")
        }

-    protected inline fun <reified T: Any?> responseBody(body: ResponseBody?, mediaType: String = JsonMediaType): T? {
-        if(body == null) return null
+    protected inline fun <reified T: Any?> responseBody(body: ResponseBody?, mediaType: String? = JsonMediaType): T? {
+        if(body == null) {
+            return null
+        }
+        val bodyContent = body.string()
+        if (bodyContent.length == 0) {
+            return null
+        }
        return when(mediaType) {
            JsonMediaType -> Moshi.Builder().add(object {
                    @ToJson
@ -62,8 +69,8 @@ open class ApiClient(val baseUrl: String) {
                    fun fromJson(s: String) = UUID.fromString(s)
                })
                .add(ByteArrayAdapter())
-                .build().adapter(T::class.java).fromJson(body.source())
-            else -> TODO()
+                .build().adapter(T::class.java).fromJson(bodyContent)
+            else ->  TODO("responseBody currently only supports JSON body.")
        }
    }

@ -80,7 +87,15 @@ open class ApiClient(val baseUrl: String) {
        }

        val url = urlBuilder.build()
-        val headers = requestConfig.headers + defaultHeaders
+
+        // take content-type/accept from spec or set to default (application/json) if not defined
+        if (requestConfig.headers[ContentType].isNullOrEmpty()) {
+            requestConfig.headers.put(ContentType, JsonMediaType)
+        }
+        if (requestConfig.headers[Accept].isNullOrEmpty()) {
+            requestConfig.headers.put(Accept, JsonMediaType)
+        }
+        val headers = requestConfig.headers

        if(headers[ContentType] ?: "" == "") {
            throw kotlin.IllegalStateException("Missing Content-Type header. This is required.")
@ -90,9 +105,8 @@ open class ApiClient(val baseUrl: String) {
            throw kotlin.IllegalStateException("Missing Accept header. This is required.")
        }

-        // TODO: support multiple contentType,accept options here.
+        // TODO: support multiple contentType options here.
        val contentType = (headers[ContentType] as String).substringBefore(";").toLowerCase()
-        val accept = (headers[Accept] as String).substringBefore(";").toLowerCase()

        var request : Request.Builder =  when (requestConfig.method) {
            RequestMethod.DELETE -> Request.Builder().url(url).delete()
@ -108,6 +122,7 @@ open class ApiClient(val baseUrl: String) {

        val realRequest = request.build()
        val response = client.newCall(realRequest).execute()
+        val accept = response.header(ContentType)?.substringBefore(";")?.toLowerCase()

        // TODO: handle specific mapping types. e.g. Map<int, Class<?>>
        when {
--- a/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/infrastructure/RequestConfig.kt
+++ b/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/infrastructure/RequestConfig.kt
@ -11,6 +11,6 @@ package org.openapitools.client.infrastructure
 data class RequestConfig(
    val method: RequestMethod,
    val path: String,
-    val headers: Map<String, String> = mapOf(),
+    val headers: MutableMap<String, String> = mutableMapOf(),
    val query: Map<String, List<String>> = mapOf()
 )
--- a/samples/client/petstore/kotlin/README.md
+++ b/samples/client/petstore/kotlin/README.md
@ -2,7 +2,7 @@

 ## Requires

-* Kotlin 1.3.20
+* Kotlin 1.3.31
 * Gradle 4.9

 ## Build
--- a/samples/client/petstore/kotlin/build.gradle
+++ b/samples/client/petstore/kotlin/build.gradle
@ -7,7 +7,7 @@ wrapper {
 }

 buildscript {
-    ext.kotlin_version = '1.3.20'
+    ext.kotlin_version = '1.3.31'

    repositories {
        mavenCentral()
@ -32,7 +32,7 @@ dependencies {
    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
    compile "com.squareup.moshi:moshi-kotlin:1.5.0"
    compile "com.squareup.moshi:moshi-adapters:1.5.0"
-    compile "com.squareup.okhttp3:okhttp:3.8.0"
-    compile "org.threeten:threetenbp:1.3.6"
+    compile "com.squareup.okhttp3:okhttp:3.14.0"
+    compile "org.threeten:threetenbp:1.3.8"
    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.1.0"
 }
--- a/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
+++ b/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
@ -14,7 +14,17 @@ package org.openapitools.client.apis
 import org.openapitools.client.models.ApiResponse
 import org.openapitools.client.models.Pet

-import org.openapitools.client.infrastructure.*
+import org.openapitools.client.infrastructure.ApiClient
+import org.openapitools.client.infrastructure.ClientException
+import org.openapitools.client.infrastructure.ClientError
+import org.openapitools.client.infrastructure.ServerException
+import org.openapitools.client.infrastructure.ServerError
+import org.openapitools.client.infrastructure.MultiValueMap
+import org.openapitools.client.infrastructure.RequestConfig
+import org.openapitools.client.infrastructure.RequestMethod
+import org.openapitools.client.infrastructure.ResponseType
+import org.openapitools.client.infrastructure.Success
+import org.openapitools.client.infrastructure.toMultiValue

 class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiClient(basePath) {

@ -27,7 +37,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun addPet(body: Pet) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/pet",
@ -58,7 +68,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun deletePet(petId: kotlin.Long, apiKey: kotlin.String?) : Unit {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf("api_key" to apiKey.toString())
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf("api_key" to apiKey.toString())
        val localVariableConfig = RequestConfig(
            RequestMethod.DELETE,
            "/pet/{petId}".replace("{"+"petId"+"}", "$petId"),
@ -89,7 +99,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun findPetsByStatus(status: kotlin.Array<kotlin.String>) : kotlin.Array<Pet> {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf("status" to toMultiValue(status.toList(), "csv"))
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/pet/findByStatus",
@ -120,7 +130,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun findPetsByTags(tags: kotlin.Array<kotlin.String>) : kotlin.Array<Pet> {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf("tags" to toMultiValue(tags.toList(), "csv"))
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/pet/findByTags",
@ -151,7 +161,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun getPetById(petId: kotlin.Long) : Pet {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/pet/{petId}".replace("{"+"petId"+"}", "$petId"),
@ -181,7 +191,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun updatePet(body: Pet) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.PUT,
            "/pet",
@ -213,7 +223,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun updatePetWithForm(petId: kotlin.Long, name: kotlin.String?, status: kotlin.String?) : Unit {
        val localVariableBody: kotlin.Any? = mapOf("name" to "$name", "status" to "$status")
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf("Content-Type" to "multipart/form-data")
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf("Content-Type" to "")
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/pet/{petId}".replace("{"+"petId"+"}", "$petId"),
@ -246,7 +256,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
    fun uploadFile(petId: kotlin.Long, additionalMetadata: kotlin.String?, file: java.io.File?) : ApiResponse {
        val localVariableBody: kotlin.Any? = mapOf("additionalMetadata" to "$additionalMetadata", "file" to "$file")
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf("Content-Type" to "multipart/form-data")
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf("Content-Type" to "")
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/pet/{petId}/uploadImage".replace("{"+"petId"+"}", "$petId"),
--- a/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
+++ b/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
@ -13,7 +13,17 @@ package org.openapitools.client.apis

 import org.openapitools.client.models.Order

-import org.openapitools.client.infrastructure.*
+import org.openapitools.client.infrastructure.ApiClient
+import org.openapitools.client.infrastructure.ClientException
+import org.openapitools.client.infrastructure.ClientError
+import org.openapitools.client.infrastructure.ServerException
+import org.openapitools.client.infrastructure.ServerError
+import org.openapitools.client.infrastructure.MultiValueMap
+import org.openapitools.client.infrastructure.RequestConfig
+import org.openapitools.client.infrastructure.RequestMethod
+import org.openapitools.client.infrastructure.ResponseType
+import org.openapitools.client.infrastructure.Success
+import org.openapitools.client.infrastructure.toMultiValue

 class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiClient(basePath) {

@ -26,7 +36,7 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
    fun deleteOrder(orderId: kotlin.String) : Unit {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.DELETE,
            "/store/order/{orderId}".replace("{"+"orderId"+"}", "$orderId"),
@ -56,7 +66,7 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
    fun getInventory() : kotlin.collections.Map<kotlin.String, kotlin.Int> {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/store/inventory",
@ -87,7 +97,7 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
    fun getOrderById(orderId: kotlin.Long) : Order {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/store/order/{orderId}".replace("{"+"orderId"+"}", "$orderId"),
@ -118,7 +128,7 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
    fun placeOrder(body: Order) : Order {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/store/order",
--- a/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
+++ b/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
@ -13,7 +13,17 @@ package org.openapitools.client.apis

 import org.openapitools.client.models.User

-import org.openapitools.client.infrastructure.*
+import org.openapitools.client.infrastructure.ApiClient
+import org.openapitools.client.infrastructure.ClientException
+import org.openapitools.client.infrastructure.ClientError
+import org.openapitools.client.infrastructure.ServerException
+import org.openapitools.client.infrastructure.ServerError
+import org.openapitools.client.infrastructure.MultiValueMap
+import org.openapitools.client.infrastructure.RequestConfig
+import org.openapitools.client.infrastructure.RequestMethod
+import org.openapitools.client.infrastructure.ResponseType
+import org.openapitools.client.infrastructure.Success
+import org.openapitools.client.infrastructure.toMultiValue

 class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiClient(basePath) {

@ -26,7 +36,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun createUser(body: User) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/user",
@ -56,7 +66,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun createUsersWithArrayInput(body: kotlin.Array<User>) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/user/createWithArray",
@ -86,7 +96,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun createUsersWithListInput(body: kotlin.Array<User>) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.POST,
            "/user/createWithList",
@ -116,7 +126,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun deleteUser(username: kotlin.String) : Unit {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.DELETE,
            "/user/{username}".replace("{"+"username"+"}", "$username"),
@ -147,7 +157,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun getUserByName(username: kotlin.String) : User {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/user/{username}".replace("{"+"username"+"}", "$username"),
@ -179,7 +189,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun loginUser(username: kotlin.String, password: kotlin.String) : kotlin.String {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf("username" to listOf("$username"), "password" to listOf("$password"))
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/user/login",
@ -208,7 +218,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun logoutUser() : Unit {
        val localVariableBody: kotlin.Any? = null
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.GET,
            "/user/logout",
@ -239,7 +249,7 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
    fun updateUser(username: kotlin.String, body: User) : Unit {
        val localVariableBody: kotlin.Any? = body
        val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf()
+        val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
        val localVariableConfig = RequestConfig(
            RequestMethod.PUT,
            "/user/{username}".replace("{"+"username"+"}", "$username"),
--- a/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
+++ b/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
@ -3,9 +3,15 @@ package org.openapitools.client.infrastructure
 import com.squareup.moshi.FromJson
 import com.squareup.moshi.Moshi
 import com.squareup.moshi.ToJson
-import okhttp3.*
+import okhttp3.OkHttpClient
+import okhttp3.RequestBody
+import okhttp3.MediaType
+import okhttp3.FormBody
+import okhttp3.HttpUrl
+import okhttp3.ResponseBody
+import okhttp3.Request
 import java.io.File
-import java.util.*
+import java.util.UUID

 open class ApiClient(val baseUrl: String) {
    companion object {
@ -13,6 +19,7 @@ open class ApiClient(val baseUrl: String) {
        protected const val Accept = "Accept"
        protected const val JsonMediaType = "application/json"
        protected const val FormDataMediaType = "multipart/form-data"
+        protected const val FormUrlEncMediaType = "application/x-www-form-urlencoded"
        protected const val XmlMediaType = "application/xml"

        @JvmStatic
@ -22,12 +29,6 @@ open class ApiClient(val baseUrl: String) {

        @JvmStatic
        val builder: OkHttpClient.Builder = OkHttpClient.Builder()
-
-        @JvmStatic
-        var defaultHeaders: Map<String, String> by ApplicationDelegates.setOnce(mapOf(ContentType to JsonMediaType, Accept to JsonMediaType))
-
-        @JvmStatic
-        val jsonHeaders: Map<String, String> = mapOf(ContentType to JsonMediaType, Accept to JsonMediaType)
    }

    protected inline fun <reified T> requestBody(content: T, mediaType: String = JsonMediaType): RequestBody =
@ -35,7 +36,7 @@ open class ApiClient(val baseUrl: String) {
            content is File -> RequestBody.create(
                MediaType.parse(mediaType), content
            )
-             mediaType == FormDataMediaType -> {
+            mediaType == FormDataMediaType || mediaType == FormUrlEncMediaType -> {
                var builder = FormBody.Builder()
                // content's type *must* be Map<String, Any>
                @Suppress("UNCHECKED_CAST")
@ -52,8 +53,14 @@ open class ApiClient(val baseUrl: String) {
            else -> TODO("requestBody currently only supports JSON body and File body.")
        }

-    protected inline fun <reified T: Any?> responseBody(body: ResponseBody?, mediaType: String = JsonMediaType): T? {
-        if(body == null) return null
+    protected inline fun <reified T: Any?> responseBody(body: ResponseBody?, mediaType: String? = JsonMediaType): T? {
+        if(body == null) {
+            return null
+        }
+        val bodyContent = body.string()
+        if (bodyContent.length == 0) {
+            return null
+        }
        return when(mediaType) {
            JsonMediaType -> Moshi.Builder().add(object {
                    @ToJson
@ -62,8 +69,8 @@ open class ApiClient(val baseUrl: String) {
                    fun fromJson(s: String) = UUID.fromString(s)
                })
                .add(ByteArrayAdapter())
-                .build().adapter(T::class.java).fromJson(body.source())
-            else -> TODO()
+                .build().adapter(T::class.java).fromJson(bodyContent)
+            else ->  TODO("responseBody currently only supports JSON body.")
        }
    }

@ -80,7 +87,15 @@ open class ApiClient(val baseUrl: String) {
        }

        val url = urlBuilder.build()
-        val headers = requestConfig.headers + defaultHeaders
+
+        // take content-type/accept from spec or set to default (application/json) if not defined
+        if (requestConfig.headers[ContentType].isNullOrEmpty()) {
+            requestConfig.headers.put(ContentType, JsonMediaType)
+        }
+        if (requestConfig.headers[Accept].isNullOrEmpty()) {
+            requestConfig.headers.put(Accept, JsonMediaType)
+        }
+        val headers = requestConfig.headers

        if(headers[ContentType] ?: "" == "") {
            throw kotlin.IllegalStateException("Missing Content-Type header. This is required.")
@ -90,9 +105,8 @@ open class ApiClient(val baseUrl: String) {
            throw kotlin.IllegalStateException("Missing Accept header. This is required.")
        }

-        // TODO: support multiple contentType,accept options here.
+        // TODO: support multiple contentType options here.
        val contentType = (headers[ContentType] as String).substringBefore(";").toLowerCase()
-        val accept = (headers[Accept] as String).substringBefore(";").toLowerCase()

        var request : Request.Builder =  when (requestConfig.method) {
            RequestMethod.DELETE -> Request.Builder().url(url).delete()
@ -108,6 +122,7 @@ open class ApiClient(val baseUrl: String) {

        val realRequest = request.build()
        val response = client.newCall(realRequest).execute()
+        val accept = response.header(ContentType)?.substringBefore(";")?.toLowerCase()

        // TODO: handle specific mapping types. e.g. Map<int, Class<?>>
        when {
--- a/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/infrastructure/RequestConfig.kt
+++ b/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/infrastructure/RequestConfig.kt
@ -11,6 +11,6 @@ package org.openapitools.client.infrastructure
 data class RequestConfig(
    val method: RequestMethod,
    val path: String,
-    val headers: Map<String, String> = mapOf(),
+    val headers: MutableMap<String, String> = mutableMapOf(),
    val query: Map<String, List<String>> = mapOf()
 )
--- a/samples/client/petstore/kotlin/src/test/kotlin/org/openapitools/client/PetApiTest.kt
+++ b/samples/client/petstore/kotlin/src/test/kotlin/org/openapitools/client/PetApiTest.kt
@ -2,8 +2,11 @@ package org.openapitools.client

 import io.kotlintest.shouldBe
 import io.kotlintest.matchers.numerics.shouldBeGreaterThan
+import io.kotlintest.matchers.string.shouldContain
+import io.kotlintest.shouldThrow
 import io.kotlintest.specs.ShouldSpec
 import org.openapitools.client.apis.PetApi
+import org.openapitools.client.infrastructure.ClientException
 import org.openapitools.client.models.Category
 import org.openapitools.client.models.Pet
 import org.openapitools.client.models.Tag
@ -11,8 +14,11 @@ import org.openapitools.client.models.Tag
 class PetApiTest : ShouldSpec() {
    init {

-        should("add a pet") {
        val petId:Long = 10006
+        val api = PetApi()
+
+        should("add a pet") {
+
            val pet = Pet(
                    id = petId,
                    name = "kotlin client test",
@ -20,15 +26,11 @@ class PetApiTest : ShouldSpec() {
                    category = Category(petId, "test kotlin category"),
                    tags = arrayOf(Tag(petId, "test kotlin tag"))
            )
-
-            val api = PetApi()
            api.addPet(pet)

        }

        should("get pet by id") {
-            val petId: Long = 10006
-            val api = PetApi()
            val result = api.getPetById(petId)

            result.id shouldBe (petId)
@ -42,7 +44,6 @@ class PetApiTest : ShouldSpec() {
        }

        should("find pet by status") {
-            val api = PetApi()
            val result = api.findPetsByStatus(arrayOf("available"))

            result.size.shouldBeGreaterThan(0)
@ -58,15 +59,12 @@ class PetApiTest : ShouldSpec() {
        }

        should("update a pet") {
-            val petId:Long = 10007
            val pet = Pet(
                    id = petId,
                    name = "kotlin client updatePet",
                    status = Pet.Status.pending,
                    photoUrls = arrayOf("http://test_kotlin_unit_test.com")
            )
-
-            val api = PetApi()
            api.updatePet(pet)

            // verify updated Pet
@ -77,14 +75,10 @@ class PetApiTest : ShouldSpec() {

        }

-        //TODO the test fail cause client doesn't support other JSON contentType/Accept
-        /*
        should("update a pet with form") {
-            val petId:Long = 10007
            val name = "kotlin client updatePet with Form"
            val status = "pending"

-            val api = PetApi()
            api.updatePetWithForm(petId, name, status)

            // verify updated Pet
@ -94,7 +88,16 @@ class PetApiTest : ShouldSpec() {
            result.status shouldBe (Pet.Status.pending)

        }
-        */
+
+        should("delete a pet") {
+            api.deletePet(petId, "apiKey")
+
+            // verify updated Pet
+            val exception = shouldThrow<ClientException> {
+                api.getPetById(petId)
+            }
+            exception.message?.shouldContain("Pet not found")
+        }

    }

--- a/samples/server/petstore/kotlin-server/ktor/src/main/kotlin/org/openapitools/server/AppMain.kt
+++ b/samples/server/petstore/kotlin-server/ktor/src/main/kotlin/org/openapitools/server/AppMain.kt
@ -1,22 +1,35 @@
 package org.openapitools.server

-import com.codahale.metrics.*
+import com.codahale.metrics.Slf4jReporter
 import com.typesafe.config.ConfigFactory
-import io.ktor.application.*
+import io.ktor.application.Application
+import io.ktor.application.ApplicationStopping
+import io.ktor.application.install
+import io.ktor.application.log
 import io.ktor.client.HttpClient
 import io.ktor.client.engine.apache.Apache
 import io.ktor.config.HoconApplicationConfig
-import io.ktor.features.*
+import io.ktor.features.AutoHeadResponse
+import io.ktor.features.Compression
+import io.ktor.features.ContentNegotiation
+import io.ktor.features.DefaultHeaders
+import io.ktor.features.HSTS
 import io.ktor.gson.GsonConverter
 import io.ktor.http.ContentType
-import io.ktor.locations.*
-import io.ktor.metrics.*
-import io.ktor.routing.*
-import java.util.concurrent.*
-import io.ktor.auth.*
+import io.ktor.locations.KtorExperimentalLocationsAPI
+import io.ktor.locations.Locations
+import io.ktor.metrics.Metrics
+import io.ktor.routing.Routing
+import java.util.concurrent.TimeUnit
+import io.ktor.auth.Authentication
+import io.ktor.auth.oauth
 import io.ktor.util.KtorExperimentalAPI
-import org.openapitools.server.infrastructure.*
-import org.openapitools.server.apis.*
+import org.openapitools.server.infrastructure.ApiKeyCredential
+import org.openapitools.server.infrastructure.ApiPrincipal
+import org.openapitools.server.infrastructure.apiKeyAuth
+import org.openapitools.server.apis.PetApi
+import org.openapitools.server.apis.StoreApi
+import org.openapitools.server.apis.UserApi


@KtorExperimentalAPI
--- a/samples/server/petstore/kotlin-server/ktor/src/main/kotlin/org/openapitools/server/Configuration.kt
+++ b/samples/server/petstore/kotlin-server/ktor/src/main/kotlin/org/openapitools/server/Configuration.kt
@ -2,8 +2,12 @@ package org.openapitools.server

 // Use this file to hold package-level internal functions that return receiver object passed to the `install` method.
 import io.ktor.auth.OAuthServerSettings
-import io.ktor.features.*
-import io.ktor.http.*
+import io.ktor.features.Compression
+import io.ktor.features.HSTS
+import io.ktor.features.deflate
+import io.ktor.features.gzip
+import io.ktor.features.minimumSize
+import io.ktor.http.HttpMethod
 import io.ktor.util.KtorExperimentalAPI
 import java.time.Duration
 import java.util.concurrent.Executors
--- a/samples/server/petstore/kotlin-server/ktor/src/main/kotlin/org/openapitools/server/Paths.kt
+++ b/samples/server/petstore/kotlin-server/ktor/src/main/kotlin/org/openapitools/server/Paths.kt
@ -11,9 +11,8 @@
 */
 package org.openapitools.server

-import io.ktor.locations.*
-import org.openapitools.server.models.*
-
+import io.ktor.locations.KtorExperimentalLocationsAPI
+import io.ktor.locations.Location

 object Paths {
    /**
--- a/samples/server/petstore/kotlin-server/ktor/src/main/kotlin/org/openapitools/server/apis/PetApi.kt
+++ b/samples/server/petstore/kotlin-server/ktor/src/main/kotlin/org/openapitools/server/apis/PetApi.kt
@ -20,10 +20,15 @@ import io.ktor.auth.OAuthAccessTokenResponse
 import io.ktor.auth.OAuthServerSettings
 import io.ktor.http.ContentType
 import io.ktor.http.HttpStatusCode
-import io.ktor.locations.*
+import io.ktor.locations.KtorExperimentalLocationsAPI
+import io.ktor.locations.delete
+import io.ktor.locations.get
 import io.ktor.response.respond
 import io.ktor.response.respondText
-import io.ktor.routing.*
+import io.ktor.routing.Route
+import io.ktor.routing.post
+import io.ktor.routing.put
+import io.ktor.routing.route

 import org.openapitools.server.Paths
 import org.openapitools.server.infrastructure.ApiPrincipal
--- a/samples/server/petstore/kotlin-server/ktor/src/main/kotlin/org/openapitools/server/apis/StoreApi.kt
+++ b/samples/server/petstore/kotlin-server/ktor/src/main/kotlin/org/openapitools/server/apis/StoreApi.kt
@ -20,10 +20,15 @@ import io.ktor.auth.OAuthAccessTokenResponse
 import io.ktor.auth.OAuthServerSettings
 import io.ktor.http.ContentType
 import io.ktor.http.HttpStatusCode
-import io.ktor.locations.*
+import io.ktor.locations.KtorExperimentalLocationsAPI
+import io.ktor.locations.delete
+import io.ktor.locations.get
 import io.ktor.response.respond
 import io.ktor.response.respondText
-import io.ktor.routing.*
+import io.ktor.routing.Route
+import io.ktor.routing.post
+import io.ktor.routing.put
+import io.ktor.routing.route

 import org.openapitools.server.Paths
 import org.openapitools.server.infrastructure.ApiPrincipal
--- a/samples/server/petstore/kotlin-server/ktor/src/main/kotlin/org/openapitools/server/apis/UserApi.kt
+++ b/samples/server/petstore/kotlin-server/ktor/src/main/kotlin/org/openapitools/server/apis/UserApi.kt
@ -20,10 +20,15 @@ import io.ktor.auth.OAuthAccessTokenResponse
 import io.ktor.auth.OAuthServerSettings
 import io.ktor.http.ContentType
 import io.ktor.http.HttpStatusCode
-import io.ktor.locations.*
+import io.ktor.locations.KtorExperimentalLocationsAPI
+import io.ktor.locations.delete
+import io.ktor.locations.get
 import io.ktor.response.respond
 import io.ktor.response.respondText
-import io.ktor.routing.*
+import io.ktor.routing.Route
+import io.ktor.routing.post
+import io.ktor.routing.put
+import io.ktor.routing.route

 import org.openapitools.server.Paths
 import org.openapitools.server.infrastructure.ApiPrincipal
--- a/samples/server/petstore/kotlin-server/ktor/src/main/kotlin/org/openapitools/server/infrastructure/ApiKeyAuth.kt
+++ b/samples/server/petstore/kotlin-server/ktor/src/main/kotlin/org/openapitools/server/infrastructure/ApiKeyAuth.kt
@ -2,8 +2,15 @@ package org.openapitools.server.infrastructure

 import io.ktor.application.ApplicationCall
 import io.ktor.application.call
-import io.ktor.auth.*
-import io.ktor.http.auth.*
+import io.ktor.auth.Authentication
+import io.ktor.auth.AuthenticationFailedCause
+import io.ktor.auth.AuthenticationPipeline
+import io.ktor.auth.AuthenticationProvider
+import io.ktor.auth.Credential
+import io.ktor.auth.Principal
+import io.ktor.auth.UnauthorizedResponse
+import io.ktor.http.auth.HeaderValueEncoding
+import io.ktor.http.auth.HttpAuthHeader
 import io.ktor.request.ApplicationRequest
 import io.ktor.response.respond

--- a/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/api/PetApi.kt
+++ b/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/api/PetApi.kt
@ -2,7 +2,13 @@ package org.openapitools.api

 import org.openapitools.model.ModelApiResponse
 import org.openapitools.model.Pet
-import io.swagger.annotations.*
+import io.swagger.annotations.Api
+import io.swagger.annotations.ApiOperation
+import io.swagger.annotations.ApiParam
+import io.swagger.annotations.ApiResponse
+import io.swagger.annotations.ApiResponses
+import io.swagger.annotations.Authorization
+import io.swagger.annotations.AuthorizationScope
 import org.springframework.http.HttpStatus
 import org.springframework.http.MediaType
 import org.springframework.http.ResponseEntity
@ -19,7 +25,13 @@ import org.springframework.web.context.request.NativeWebRequest
 import org.springframework.beans.factory.annotation.Autowired

 import javax.validation.Valid
-import javax.validation.constraints.*
+import javax.validation.constraints.DecimalMax
+import javax.validation.constraints.DecimalMin
+import javax.validation.constraints.Max
+import javax.validation.constraints.Min
+import javax.validation.constraints.NotNull
+import javax.validation.constraints.Pattern
+import javax.validation.constraints.Size

 import kotlin.collections.List
 import kotlin.collections.Map
--- a/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/api/StoreApi.kt
+++ b/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/api/StoreApi.kt
@ -1,7 +1,13 @@
 package org.openapitools.api

 import org.openapitools.model.Order
-import io.swagger.annotations.*
+import io.swagger.annotations.Api
+import io.swagger.annotations.ApiOperation
+import io.swagger.annotations.ApiParam
+import io.swagger.annotations.ApiResponse
+import io.swagger.annotations.ApiResponses
+import io.swagger.annotations.Authorization
+import io.swagger.annotations.AuthorizationScope
 import org.springframework.http.HttpStatus
 import org.springframework.http.MediaType
 import org.springframework.http.ResponseEntity
@ -18,7 +24,13 @@ import org.springframework.web.context.request.NativeWebRequest
 import org.springframework.beans.factory.annotation.Autowired

 import javax.validation.Valid
-import javax.validation.constraints.*
+import javax.validation.constraints.DecimalMax
+import javax.validation.constraints.DecimalMin
+import javax.validation.constraints.Max
+import javax.validation.constraints.Min
+import javax.validation.constraints.NotNull
+import javax.validation.constraints.Pattern
+import javax.validation.constraints.Size

 import kotlin.collections.List
 import kotlin.collections.Map
--- a/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/api/UserApi.kt
+++ b/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/api/UserApi.kt
@ -1,7 +1,13 @@
 package org.openapitools.api

 import org.openapitools.model.User
-import io.swagger.annotations.*
+import io.swagger.annotations.Api
+import io.swagger.annotations.ApiOperation
+import io.swagger.annotations.ApiParam
+import io.swagger.annotations.ApiResponse
+import io.swagger.annotations.ApiResponses
+import io.swagger.annotations.Authorization
+import io.swagger.annotations.AuthorizationScope
 import org.springframework.http.HttpStatus
 import org.springframework.http.MediaType
 import org.springframework.http.ResponseEntity
@ -18,7 +24,13 @@ import org.springframework.web.context.request.NativeWebRequest
 import org.springframework.beans.factory.annotation.Autowired

 import javax.validation.Valid
-import javax.validation.constraints.*
+import javax.validation.constraints.DecimalMax
+import javax.validation.constraints.DecimalMin
+import javax.validation.constraints.Max
+import javax.validation.constraints.Min
+import javax.validation.constraints.NotNull
+import javax.validation.constraints.Pattern
+import javax.validation.constraints.Size

 import kotlin.collections.List
 import kotlin.collections.Map
--- a/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/model/Category.kt
+++ b/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/model/Category.kt
@ -2,8 +2,13 @@ package org.openapitools.model

 import java.util.Objects
 import com.fasterxml.jackson.annotation.JsonProperty
-import javax.validation.Valid
-import javax.validation.constraints.*
+import javax.validation.constraints.DecimalMax
+import javax.validation.constraints.DecimalMin
+import javax.validation.constraints.Max
+import javax.validation.constraints.Min
+import javax.validation.constraints.NotNull
+import javax.validation.constraints.Pattern
+import javax.validation.constraints.Size
 import io.swagger.annotations.ApiModelProperty

 /**
--- a/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/model/ModelApiResponse.kt
+++ b/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/model/ModelApiResponse.kt
@ -2,8 +2,13 @@ package org.openapitools.model

 import java.util.Objects
 import com.fasterxml.jackson.annotation.JsonProperty
-import javax.validation.Valid
-import javax.validation.constraints.*
+import javax.validation.constraints.DecimalMax
+import javax.validation.constraints.DecimalMin
+import javax.validation.constraints.Max
+import javax.validation.constraints.Min
+import javax.validation.constraints.NotNull
+import javax.validation.constraints.Pattern
+import javax.validation.constraints.Size
 import io.swagger.annotations.ApiModelProperty

 /**
--- a/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/model/Order.kt
+++ b/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/model/Order.kt
@ -3,8 +3,13 @@ package org.openapitools.model
 import java.util.Objects
 import com.fasterxml.jackson.annotation.JsonProperty
 import com.fasterxml.jackson.annotation.JsonValue
-import javax.validation.Valid
-import javax.validation.constraints.*
+import javax.validation.constraints.DecimalMax
+import javax.validation.constraints.DecimalMin
+import javax.validation.constraints.Max
+import javax.validation.constraints.Min
+import javax.validation.constraints.NotNull
+import javax.validation.constraints.Pattern
+import javax.validation.constraints.Size
 import io.swagger.annotations.ApiModelProperty

 /**
--- a/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/model/Pet.kt
+++ b/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/model/Pet.kt
@ -5,8 +5,13 @@ import com.fasterxml.jackson.annotation.JsonProperty
 import com.fasterxml.jackson.annotation.JsonValue
 import org.openapitools.model.Category
 import org.openapitools.model.Tag
-import javax.validation.Valid
-import javax.validation.constraints.*
+import javax.validation.constraints.DecimalMax
+import javax.validation.constraints.DecimalMin
+import javax.validation.constraints.Max
+import javax.validation.constraints.Min
+import javax.validation.constraints.NotNull
+import javax.validation.constraints.Pattern
+import javax.validation.constraints.Size
 import io.swagger.annotations.ApiModelProperty

 /**
--- a/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/model/Tag.kt
+++ b/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/model/Tag.kt
@ -2,8 +2,13 @@ package org.openapitools.model

 import java.util.Objects
 import com.fasterxml.jackson.annotation.JsonProperty
-import javax.validation.Valid
-import javax.validation.constraints.*
+import javax.validation.constraints.DecimalMax
+import javax.validation.constraints.DecimalMin
+import javax.validation.constraints.Max
+import javax.validation.constraints.Min
+import javax.validation.constraints.NotNull
+import javax.validation.constraints.Pattern
+import javax.validation.constraints.Size
 import io.swagger.annotations.ApiModelProperty

 /**
--- a/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/model/User.kt
+++ b/samples/server/petstore/kotlin-springboot/src/main/kotlin/org/openapitools/model/User.kt
@ -2,8 +2,13 @@ package org.openapitools.model

 import java.util.Objects
 import com.fasterxml.jackson.annotation.JsonProperty
-import javax.validation.Valid
-import javax.validation.constraints.*
+import javax.validation.constraints.DecimalMax
+import javax.validation.constraints.DecimalMin
+import javax.validation.constraints.Max
+import javax.validation.constraints.Min
+import javax.validation.constraints.NotNull
+import javax.validation.constraints.Pattern
+import javax.validation.constraints.Size
 import io.swagger.annotations.ApiModelProperty

 /**