[JAVA] No validator could be found for constraint '@Size` on enum type

Description

If a Swagger spec declares an enum but also specifies a maxLength, running swagger-codegen with useBeanValidation enabled, will tag the enum with @Size constraint. Invoking validation on the generated model will result in this Java error: HV000030: No validator could be found for constraint 'jakarta.validation.constraints.Size' validating type

The reason for the failure is that @Size can only be used to enforce validation on String or Collections, so if it's used on an enum type, the jakarta library will panic.

Swagger-codegen version

The issue is observed in version 3.0.62

Swagger declaration file content or URL

My Swagger spec contains this enum declaration:

        Status:
          type: "string"
          maxLength: 10
          description: "status of something"
          enum:
            - "PENDING"
            - "COMPLETED"

Command line used for generation

This command was run on mac using the latest swagger-codegen installed using brew:

swagger-codegen generate -i sample.yaml -l java --additional-properties useBeanValidation=true -o ./build

$ swagger-codegen version
3.0.62

Steps to reproduce

1. Find a swagger spec that contains enum with maxLenghh or add one to any swagger spec.
2. Run the command above to generate JAVA code with bean validation.
3. Invoke the validation on the model containing the enum using Validation.buildDefaultValidatorFactory().getValidator().validate(toValidate);

Related issues/PRs

N/A

Suggest a fix/enhancement

SImple fix: remove maxLength from the enum declaration, or remove @Size manually in the generated model. However it would be good for swagger-codgen to handle this sensibly.

Perhaps we can update the mustache template to add @Size for non-enum type like this:

{{#minLength}}{{#maxLength}}{{^isEnum}} @Size(min={{minLength}},max={{maxLength}}){{/isEnum}}{{/maxLength}}{{/minLength}}

Inspect modules/swagger-codegen/src/main/resources/Java/beanValidationCore.mustache, especially the @Size rendering mentioned in the issue. Generate Java code from an enum with maxLength using useBeanValidation=true, then validate the generated model; done means enum types no longer receive an invalid @Size constraint while other applicable types retain it.