openapi-generator/customization.md

Customization

Modifying the client library format

Don't like the default client syntax? Want a different language supported? No problem! OpenAPI Generator processes mustache templates with the jmustache engine. You can modify our templates or make your own.

You can look at modules/openapi-generator/src/main/resources/${your-language} for examples. To make your own templates, create your own files and use the -t flag to specify your template folder. It actually is that easy.

Making your own codegen modules

If you're starting a project with a new language and don't see what you need, openapi-generator can help you create a project to generate your own libraries:

java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar meta \
  -o output/myLibrary -n myClientCodegen -p com.my.company.codegen

This will write, in the folder output/myLibrary, all the files you need to get started, including a `README.md. Once modified and compiled, you can load your library with the codegen and generate clients with your own, custom-rolled logic.

You would then compile your library in the output/myLibrary folder with mvn package and execute the codegen like such:

java -cp output/myLibrary/target/myClientCodegen-openapi-generator-1.0.0.jar:modules/openapi-generator-cli/target/openapi-generator-cli.jar org.openapitools.codegen.OpenAPIGenerator

For Windows users, you will need to use ; instead of : in the classpath, e.g.

java -cp output/myLibrary/target/myClientCodegen-openapi-generator-1.0.0.jar;modules/openapi-generator-cli/target/openapi-generator-cli.jar org.openapitools.codegen.OpenAPIGenerator

Note the myClientCodegen is an option now, and you can use the usual arguments for generating your library:

java -cp output/myLibrary/target/myClientCodegen-openapi-generator-1.0.0.jar:modules/openapi-generator-cli/target/openapi-generator-cli.jar \
  io.openapitools.codegen.OpenAPIGenerator generate -l myClientCodegen\
  -i https://raw.githubusercontent.com/openapitools/openapi-generator/master/modules/openapi-generator/src/test/resources/2_0/petstore.yaml \
  -o myClient

Selective generation

You may not want to generate all models in your project. Likewise you may want just one or two apis to be written. If that's the case, you can use system properties to control the output:

The default is generate everything supported by the specific library. Once you enable a feature, it will restrict the contents generated:

# generate only models
java -Dmodels {opts}

# generate only apis
java -Dapis {opts}

# generate only supporting files
java -DsupportingFiles

# generate models and supporting files
java -Dmodels -DsupportingFiles

To control the specific files being generated, you can pass a CSV list of what you want:

# generate the User and Pet models only
-Dmodels=User,Pet

# generate the User model and the supportingFile `StringUtil.java`:
-Dmodels=User -DsupportingFiles=StringUtil.java

To control generation of docs and tests for api and models, pass false to the option. For api, these options are -DapiTests=false and -DapiDocs=false. For models, -DmodelTests=false and -DmodelDocs=false. These options default to true and don't limit the generation of the feature options listed above (like -Dapi):

# generate only models (with tests and documentation)
java -Dmodels {opts}

# generate only models (with tests but no documentation)
java -Dmodels -DmodelDocs=false {opts}

# generate only User and Pet models (no tests and no documentation)
java -Dmodels=User,Pet -DmodelTests=false {opts}

# generate only apis (without tests)
java -Dapis -DapiTests=false {opts}

# generate only apis (modelTests option is ignored)
java -Dapis -DmodelTests=false {opts}

When using selective generation, only the templates needed for the specific generation will be used.

Ignore file format

OpenAPI Generator supports a .openapi-generator-ignore file, similar to .gitignore or .dockerignore you're probably already familiar with.

The ignore file allows for better control over overwriting existing files than the --skip-overwrite flag. With the ignore file, you can specify individual files or directories can be ignored. This can be useful, for example if you only want a subset of the generated code.

Examples:

# OpenAPI Generator Ignore
# Lines beginning with a # are comments

# This should match build.sh located anywhere.
build.sh

# Matches build.sh in the root
/build.sh

# Exclude all recursively
docs/**

# Explicitly allow files excluded by other rules
!docs/UserApi.md

# Recursively exclude directories named Api
# You can't negate files below this directory.
src/**/Api/

# When this file is nested under /Api (excluded above),
# this rule is ignored because parent directory is excluded by previous rule.
!src/**/PetApiTests.cs

# Exclude a single, nested file explicitly
src/Org.OpenAPITools.Test/Model/AnimalFarmTests.cs

The .openapi-generator-ignore file must exist in the root of the output directory.

Upon first code generation, you may also pass the CLI option --ignore-file-override=/path/to/ignore_file for greater control over generated outputs. Note that this is a complete override, and will override the .openapi-generator-ignore file in an output directory when regenerating code.

Editor support for .openapi-generator-ignore files is available in IntelliJ via the .ignore plugin.

Customizing the generator

There are different aspects of customizing the code generator beyond just creating or modifying templates. Each language has a supporting configuration file to handle different type mappings, etc:

$ ls -1 modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/
AbstractJavaJAXRSServerCodegen.java
AbstractTypeScriptClientCodegen.java
... (results omitted)
TypeScriptAngularClientCodegen.java
TypeScriptNodeClientCodegen.java

Each of these files creates reasonable defaults so you can get running quickly. But if you want to configure package names, prefixes, model folders, etc. you can use a json config file to pass the values.

java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar generate \
  -i https://raw.githubusercontent.com/openapitools/openapi-generator/master/modules/openapi-generator/src/test/resources/2_0/petstore.yaml \
  -l java \
  -o samples/client/petstore/java \
  -c path/to/config.json

and config.json contains the following as an example:

{
  "apiPackage" : "petstore"
}

Supported config options can be different per language. Running config-help -l {lang} will show available options. These options are applied via configuration file (e.g. config.json) or by passing them with -D{optionName}={optionValue}. (If -D{optionName} does not work, please open a ticket and we'll look into it)

java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar config-help -l java

Output

CONFIG OPTIONS
	modelPackage
	    package for generated models

	apiPackage
	    package for generated api classes
...... (results omitted)
	library
	    library template (sub-template) to use:
	    jersey1 - HTTP client: Jersey client 1.18. JSON processing: Jackson 2.4.2
	    jersey2 - HTTP client: Jersey client 2.6
	    feign - HTTP client: Netflix Feign 8.1.1.  JSON processing: Jackson 2.6.3
	    okhttp-gson (default) - HTTP client: OkHttp 2.4.0. JSON processing: Gson 2.3.1
	    retrofit - HTTP client: OkHttp 2.4.0. JSON processing: Gson 2.3.1 (Retrofit 1.9.0)
        retrofit2 - HTTP client: OkHttp 2.5.0. JSON processing: Gson 2.4 (Retrofit 2.0.0-beta2)
        google-api-client - HTTP client: google-api-client 1.23.0. JSON processing: Jackson 2.8.9
        rest-assured - HTTP client: rest-assured : 3.1.0. JSON processing: Gson 2.6.1. Only for Java8

Your config file for Java can look like

{
  "groupId":"com.my.company",
  "artifactId":"MyClient",
  "artifactVersion":"1.2.0",
  "library":"feign"
}

For all the unspecified options default values will be used.

Another way to override default options is to extend the config class for the specific language. To change, for example, the prefix for the Objective-C generated files, simply subclass the ObjcClientCodegen.java:

package com.mycompany.openapitools.codegen;

import org.openapitools.codegen.languages.*;

public class MyObjcCodegen extends ObjcClientCodegen {
    static {
        PREFIX = "HELO";
    }
}

and specify the classname when running the generator:

-l com.mycompany.openapitools.codegen.MyObjcCodegen

Your subclass will now be loaded and overrides the PREFIX value in the superclass.

Bringing your own models

Sometimes you don't want a model generated. In this case, you can simply specify an import mapping to tell the codegen what not to create. When doing this, every location that references a specific model will refer back to your classes. Note, this may not apply to all languages...

To specify an import mapping, use the --import-mappings argument and specify the model-to-import logic as such:

--import-mappings Pet=my.models.MyPet

Or for multiple mappings:

--import-mappings Pet=my.models.MyPet,Order=my.models.MyOrder

or

--import-mappings Pet=my.models.MyPet --import-mappings Order=my.models.MyOrder