[BUG][java-micronaut-server] Multipart property file is renamed to _file and affect the name

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?

Description

Because file is reserved word (see AbstractJavaCodegen.java#L180) in AbstractJavaCodegen so it is replaced/escaped with _file. Therefore if you use a property in multipar/form-data with a name file it is generated in java-micronaut-server as a parameter CompletedFileUpload _file and Micronaut it as the multipart name. It does not work if you send a request with the name file and the parameter is always null. If you send the same requests but change the name to _file it works. But it does not match to OpenaAPI.

openapi-generator version

I use the latest version OpenAPI Generator with maven plugin v6.6.0. I also tried master branch.

OpenAPI declaration

I have this request body definition:

requestBody:
  content: 
    multipart/form-data:
      schema:
        type: object
        properties:
          name:
            type: string
          file:
            type: string
            format: binary

Generated Code

public void upload(
  String name,
  CompletedFileUpload _file // always null because wrong name
)

Steps to reproduce

1. Create multipart request with a property name file
2. Generate code with java-micronaut-server
3. Try to call it with the file and it fails

Suggest a fix

Add @Part("file") annotation to _file parameter.

@Part("file") CompletedFileUpload _file

Start with the java-micronaut-server generation entry point and the reserved-word handling described in AbstractJavaCodegen.java#L180. Reproduce the multipart request using the provided YAML, then verify that the generated parameter preserves the OpenAPI property name through its Micronaut annotation and accepts a request using file.