[Feature][Java/Spring] Support Discriminator Based OneOf Interface

[cachescrubber]

Support Discriminator Based OneOf Interface

Superseeds

• [Spring][server] oneOf Interface for Spring Boot #10392, which is in turn based on
• [Spring][server] oneOf Interface for Spring Boot #8091

Also Fixes

• [REQ][spring] Feature x-implements is not supported #11636

Brings basic discriminator based OneOf Support to the JavaSpring generator. It generates a marker Interface which the oneOf Models then implement. Technically it requires Jackson based models and is implemented using @JsonTypeInfo and @JsonSubTypes based using a discriminator property.

The relevant Code ist moved to AbstractJavaCodegen and aligned with the other Java based generators in the hierarchy.

The oneOf Support is implemented by utilizing the x-implements vendor extension.

Currently It is enabled in the SpringCodegen only:

useOneOfInterfaces = true;
legacyDiscriminatorBehavior = false;

Synopsis

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "@type", visible = true)
@JsonSubTypes({
  @JsonSubTypes.Type(value = Foo.class, name = "Foo"),
  @JsonSubTypes.Type(value = FooRef.class, name = "FooRef")
})

@Generated(value = "org.openapitools.codegen.languages.SpringCodegen")
public interface FooRefOrValue {
    public String getAtType();
}

PR checklist

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[cachescrubber]

Example for inheritance using discriminator

[cachescrubber]

Example: Inherit from EntityRef class using discriminator an implementing the oneOf Interface.

[cachescrubber]

The OneOf Interface

[welshm]

Makes sense overall - I do wonder how nested oneOf will work

[jburgess]

@cachescrubber Thank you so much for picking this up and keeping it up-to-date with the base branch! Initial testing looks good on this PR.

@wing328 Can we get this in a milestone?

[welshm]

Is this still necessary after #11784 ?

[cachescrubber]

Yes, very much so. It the model entity is a one-of-interface, a public interface MyModel is generated instead of a public class myModel. Or do I miss something?

[wing328]

@cachescrubber thanks for the PR. Here are something we discussed before and put it here so that everyone is on the same page:

• implementation by this PR does not support primitive type, e.g.

    IntOrString:
      oneOf:
        - type: string
        - type: integer   

• oneOf does not imply inheritance

[wing328]

Also just to add that java (okhttp-gson, jersey2, native) client generator has a different implementation of oneOf, anyOf.

We can give this PR (implementation) a try and collect feedback from our users.

[cachescrubber]

@wing328. Thanks for the review and merging!