[Java] Fix issue 22209 oneof pojo

[Chhida]

fixes #22209

• Add useOneOfPojo option to generate real POJO classes for oneOf schemas instead of wrapper models

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---

Summary by cubic

Adds a useOneOfPojo option to Java generators to emit real POJO classes for oneOf schemas instead of abstract wrapper models, fixing oneOf inheritance and serialization issues. Fixes #22209. Adds a Jersey3 sample and config to demonstrate the option.

• New Features

  • New additional-property useOneOfPojo (default: false).
  • When enabled, oneOf models are generated as concrete POJOs; wrapper model is not created.
  • Overrides updateModelForComposedSchema() to skip merging for oneOf and restore original vars; option handled in processOpts(); CLI option added; docs updated across Java generators.
  • Added bin/configs/java-jersey3-oneOf-pojo.yaml and samples/client/petstore/java/jersey3-oneOf-pojo/ to validate output.

• Migration

  • Opt-in by passing --additional-properties useOneOfPojo=true (or set in config). No breaking changes by default.

^{Written for commit 7830618. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 118 files

Note: This PR contains a large number of files. cubic only reviews up to 75 files per PR, so some files may not have been reviewed. cubic prioritises the most important files to review.

[cubic-dev-ai]

7 issues found across 47 files (changes from recent commits).

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="samples/client/petstore/java/jersey3-oneOf-pojo/src/main/java/org/openapitools/client/Configuration.java">

<violation number="1" location="samples/client/petstore/java/jersey3-oneOf-pojo/src/main/java/org/openapitools/client/Configuration.java:39">
P2: `AtomicReference.updateAndGet` callback invokes a potentially side-effectful supplier, which may run multiple times under contention.</violation>
</file>

<file name="samples/client/petstore/java/jersey3-oneOf-pojo/README.md">

<violation number="1" location="samples/client/petstore/java/jersey3-oneOf-pojo/README.md:18">
P2: README minimum Java version is incorrect for the Jersey 3.1 dependency baseline.</violation>
</file>

<file name="samples/client/petstore/java/jersey3-oneOf-pojo/src/main/java/org/openapitools/client/RFC3339JavaTimeModule.java">

<violation number="1" location="samples/client/petstore/java/jersey3-oneOf-pojo/src/main/java/org/openapitools/client/RFC3339JavaTimeModule.java:32">
P2: Custom deserializers are registered after `super.setupModule(context)`, so they may not be applied to the mapper during module registration.</violation>
</file>

<file name="samples/client/petstore/java/jersey3-oneOf-pojo/git_push.sh">

<violation number="1" location="samples/client/petstore/java/jersey3-oneOf-pojo/git_push.sh:42">
P2: The script checks for any remote instead of specifically checking for `origin`, which can cause pull/push failures when only non-`origin` remotes exist.</violation>

<violation number="2" location="samples/client/petstore/java/jersey3-oneOf-pojo/git_push.sh:48">
P2: Access token is embedded in the Git remote URL, risking plaintext secret exposure in `.git/config` and related tooling.</violation>

<violation number="3" location="samples/client/petstore/java/jersey3-oneOf-pojo/git_push.sh:57">
P2: `git push` failures can be masked because the script returns the pipeline/`grep` status instead of the push command status.</violation>
</file>

<file name="samples/client/petstore/java/jersey3-oneOf-pojo/src/main/java/org/openapitools/client/ApiClient.java">

<violation number="1" location="samples/client/petstore/java/jersey3-oneOf-pojo/src/main/java/org/openapitools/client/ApiClient.java:851">
P2: Form-urlencoded serialization overwrites accumulated parameters, causing only the last field to be sent.</violation>
</file>

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[jpfinne]

@Chhida I don't think the generated code will work.
For example, how to use SchemaA in public ApiResponse<Void> rootPostWithHttpInfo(@jakarta.annotation.Nullable PostRequest postRequest) throws ApiException ?

The inline oneOf complexifies the generation. This is simpler:

components:
  schemas:
    schemaA:
      properties:
        propA:
          type: string
      type: object
    __post_request:
      oneOf:
        - $ref: "#/components/schemas/schemaA"
        - $ref: "#/components/schemas/SchemaAdditional"
    SchemaAdditional:
      additionalProperties: true
      properties: {}
      type: object

The spring generator has an option USE_DEDUCTION_FOR_ONE_OF_INTERFACES

For example:

generateFromContract(
      "src/test/resources/3_0/spring/issue_22209.yaml", SPRING_BOOT,
      Map.of(USE_DEDUCTION_FOR_ONE_OF_INTERFACES, true,
              USE_ONE_OF_INTERFACES, true,
              GENERATE_ALIAS_AS_MODEL, true));

It generates:

@JsonTypeInfo(use = JsonTypeInfo.Id.DEDUCTION)
@JsonSubTypes({
    @JsonSubTypes.Type(value = SchemaA.class), 
    @JsonSubTypes.Type(value = SchemaAdditional.class)
})
public interface PostRequest {
}

I would implement USE_DEDUCTION_FOR_ONE_OF_INTERFACES for the java generators:

• move USE_DEDUCTION_FOR_ONE_OF_INTERFACES to AbstractJavaCodegen
• add the logic in modules/openapi-generator/src/main/resources/Java/oneof_interface.mustache. See modules/openapi-generator/src/main/resources/JavaSpring/oneof_interface.mustache