[Java][Spring] fix one of

Created by: Orachigami

Fixes: https://github.com/OpenAPITools/openapi-generator/issues/2906 Fixes: https://github.com/OpenAPITools/openapi-generator/issues/5381 Fixes: https://github.com/OpenAPITools/openapi-generator/issues/8647 Fixes: https://github.com/OpenAPITools/openapi-generator/issues/8860 Fixes: https://github.com/OpenAPITools/openapi-generator/issues/9601 Fixes: https://github.com/OpenAPITools/openapi-generator/issues/9981

Added tests oneOfModelsGeneration for Java Spring and Java Client which iterate through several specs with OneOf usage cases and check that OneOf models are generated and subtypes implement generated models. Java Client test also creates a cartesian product of specs and client libraries for regress tests.

How inline OneOf models generation is fixed

Added x-deduction and x-deduction-model-names for vendorExtensions. These extensions are used to generated Jackson annotation when the discriminator cannot be used. The discriminator uses the specific field value for deserialization decisions. However, according to the https://swagger.io/specification#discriminator-object first example, oneOf can be used without the discriminator object. This case can be handled with Jackson recently added JsonTypeInfo.Id.DEDUCTION option. DEDUCTION option forces Jackson to make deserialization decisions according to the available fields in the payload and Models which implement oneOf interface/class.

ToDo

• Polymorphic primitives deserialization

Example output screenshots

Output examples

Specification usage	OneOf code	Model code

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