Allow the user to specify a preferred Media Type

Description

This is a feature request to allow the user to specify their preferred Media Type when generating a client from a Swagger spec. Currently, if the Swagger spec defines multiple media types for consumes or produces in a given path, the user has no way to specify which type should be used at runtime. For example, if the spec states that a path supports both application/xml and application/json, there's no way for the user to indicate which type they want to use.

In theory, it shouldn't matter which type is used, since the service supports both. In practice, many companies have corporate standards that require a specific media type to be used.

My proposal is to add a new config option preferredMediaType. For each path in the Swagger spec, if the path supports the preferred type, then that type will be used. If the path does not support the preferred type, then one of the supported types will be used by following the logic as currently implemented.

Swagger-codegen version

We're using 2.4.8, but this feature could also be applied to 3.0.11

Swagger declaration file content or url

https://gist.github.com/packleader/30f9f0b6602ab749af1998787c6f72c5

Command line used for generation

java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate \
  -i swagger.yaml \
  -l java \
  -o temp/client/petstore/java

Steps to reproduce

The resulting code will always use application/json. Although DefaultApi has both application/json and application/xml, ApiClient will always use application/json due to the logic in selectHeaderAccept and selectHeaderContentType.

Related issues/PRs

Suggest a fix/enhancement

I'll volunteer to implement this feature, and my proposed implementation is as follows:

• Add a new property preferredMediaType to CodegenConfig
• Add a new property preferredMediaType to CodeGenMojo
• In DefaultCodegen::fromOperation, compare consumes to preferredMediaType. If preferredMediaType is not null and consumes contains preferredMediaType, then consumes = Arrays.asList(preferredMediaType). Otherwise, BAU.
• Apply the same logic to produces.
• Update documentation as needed.

The above algorithm will ensure that if a given path supports preferredMediaType, then only preferredMediaType will be included in the generated code. Otherwise, the generated code will be same as BAU.

Start with CodegenConfig, CodeGenMojo, and DefaultCodegen::fromOperation, then trace how consumes and produces reach the generated ApiClient methods selectHeaderAccept and selectHeaderContentType. Confirm the behavior using the provided Swagger declaration and Java generation command. Done means preferredMediaType is configurable, preferred when supported, falls back to existing selection otherwise, and documentation is updated.