Clone OpenAPI Generator and navigate to `modules/openapi-generator/src/main/resources/${template}`, where `${template}` is the name of the generator you wish to modify. For example, if you are looking for the C# template, it's named `csharp`. This directory contains all the templates used to generate your target client/server/doc output.
Templates consist of multiple mustache files. [Mustache](https://mustache.github.io/) is used as the templating language for these templates, and the specific engine used is [jmustache](https://github.com/samskivert/jmustache).
If you wish to modify one of these templates, copy and paste the template you're interested in to a templates directory you control. To let OpenAPI Generator know where this templates directory is, use the `-t` option (e.g: `-t ./templates/`).
_**Note:** You cannot use this approach to create new templates, only override existing ones. If you'd like to create a new generator within the project, see `new.sh` in the repository root._
This will create a new directory `out/generators/my-codegen`, with all the files you need to get started - including a `README.md`. Once modified and compiled, you can use your new codegen just like any other, with your own custom-rolled logic.
These names can be anything you like. If you are building a client for the whitespace language, maybe you'd use the options `-o out/generators/whitespace -n whitespace`. They can be the same, or different, it doesn't matter. The `-n` value will be become the template name.
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:
```sh
# 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:
```sh
# 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`):
```sh
# 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.
To skip models defined as the form parameters in "requestBody", please use `skipFormModel` (default to false) (this option is introduced at v3.2.2)
```sh
java -DskipFormModel=true
```
This option will be helpful to skip model generation due to the form parameter, which is defined differently in OAS3 as there's no form parameter in OAS3
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.
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](https://plugins.jetbrains.com/plugin/7495--ignore).
### 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:
```sh
$ 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.
**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](https://github.com/openapitools/openapi-generator/issues/new) and we'll look into it)
