[BUG][SPRING] Spring's validation behavior is different depending on how annotations are used

Description

Spring's behavior is different depending on whether @Validated is present on the class-level:

• If it's present, ConstraintViolationException is thrown if there are validation errors.
• If it's not present, MethodArgumentNotValidException is thrown if there are validation errors.

This affects the way validation errors are converted to response to clients because the conversion implementation needs to be completely different.

openapi-generator version

openapi-generator-maven-plugin:4.1.2

Command line used for generation

Plugin configuration used:

                <configuration>
                    <inputSpec>${project.basedir}/../../api/service-api/src/main/resources/openapi.yaml</inputSpec>
                    <output>${project.build.directory}/generated-sources/api</output>
                    <generateSupportingFiles>true</generateSupportingFiles>
                    <generatorName>spring</generatorName>
                    <strictSpec>true</strictSpec>
                    <configOptions>
                        <apiPackage>mypackage</apiPackage>
                        <modelPackage>mypackage</modelPackage>                        
                        <library>spring-mvc</library>
                        <dateLibrary>legacy</dateLibrary>
                        <interfaceOnly>true</interfaceOnly>
                        <skipDefaultInterface>true</skipDefaultInterface>
                        <useBeanValidation>true</useBeanValidation>
                        <useTags>true</useTags>
                        <java8>true</java8>
                        <useOptional>false</useOptional>
                    </configOptions>
                </configuration>

Steps to reproduce

Just enable or disable useBeanValidation to see that @Validated gets added to the Api interface.

Suggest a fix

Add a flag to indicate whether class-level @Validated should be added and make it true by default to maintain backwards compatibility.

Start with the Spring generator's handling of the useBeanValidation option and inspect the generated Api interface to see where class-level @Validated is added. Review the related generator configuration and tests, if present; done means class-level @Validated behavior is configurable while preserving the requested backwards-compatible default.