Swagger UI not accessible when FormattingConversionService is a CGLIB proxy

[wollefitz]

Describe the bug

When formattingConversionService is an instance of an CGLIB proxy, I can't open the Swagger UI. It only displays an error "Internal Server Error /v3/api-docs/api". In the application logs, one can see the following output:

java.lang.NullPointerException: Cannot invoke "Object.getClass()" because "converters" is null
	at org.springdoc.core.providers.WebConversionServiceProvider.getSpringConvertedType(WebConversionServiceProvider.java:118)
	at org.springdoc.core.GenericParameterService.calculateSchema(GenericParameterService.java:360)
	at org.springdoc.core.AbstractRequestService.buildParam(AbstractRequestService.java:530)
	at org.springdoc.core.AbstractRequestService.buildParams(AbstractRequestService.java:490)
	at org.springdoc.core.AbstractRequestService.build(AbstractRequestService.java:312)
	at org.springdoc.api.AbstractOpenApiResource.calculatePath(AbstractOpenApiResource.java:472)
	at org.springdoc.api.AbstractOpenApiResource.calculatePath(AbstractOpenApiResource.java:636)
	at org.springdoc.webmvc.api.OpenApiResource.lambda$calculatePath$11(OpenApiResource.java:219)
	at java.base/java.util.Optional.ifPresent(Optional.java:178)
	at org.springdoc.webmvc.api.OpenApiResource.calculatePath(OpenApiResource.java:200)
	at org.springdoc.webmvc.api.OpenApiResource.lambda$getPaths$2(OpenApiResource.java:170)
	at java.base/java.util.Optional.ifPresent(Optional.java:178)
	at org.springdoc.webmvc.api.OpenApiResource.getPaths(OpenApiResource.java:149)
	at org.springdoc.api.AbstractOpenApiResource.getOpenApi(AbstractOpenApiResource.java:331)
	at org.springdoc.webmvc.api.OpenApiResource.openapiJson(OpenApiResource.java:124)
	at org.springdoc.webmvc.api.OpenApiWebMvcResource.openapiJson(OpenApiWebMvcResource.java:110)
	at org.springdoc.webmvc.api.MultipleOpenApiWebMvcResource.openapiJson(MultipleOpenApiWebMvcResource.java:93)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
	at java.base/java.lang.reflect.Method.invoke(Method.java:578)
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205)
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150)
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808)
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1072)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:965)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
	... 111 common frames omitted

The underlying issue is that the converters field of formattingConversionService is accessed via reflection, see

springdoc-openapi/springdoc-openapi-common/src/main/java/org/springdoc/core/providers/WebConversionServiceProvider.java

Lines 113 to 118 in f8c9762

	Field convertersField = FieldUtils.getDeclaredField(GenericConversionService.class, CONVERTERS, true);
	if (convertersField != null) {
	Object converters;
	try {
	converters = convertersField.get(formattingConversionService);
	convertersField = FieldUtils.getDeclaredField(converters.getClass(), CONVERTERS, true);

In Spring, CGLIB proxies do not inherit any instance variables resulting into a null value when accessing the converters field.

This bug was introduced in #1534.

To Reproduce
Steps to reproduce the behavior:

• What version of spring-boot you are using?
  2.7.12

• What modules and versions of springdoc-openapi are you using?
  1.7.0 version of springdoc-openapi-common and springdoc-openapi-ui

• Provide with a sample code (HelloController) or Test that reproduces the problem
  An application that throws the mentioned error can be found here: https://github.com/wollefitz/springdoc-openapi-demo

Expected behavior

• A clear and concise description of what you expected to happen.

I'm able to open the Swagger UI at http://server:port/context-path/swagger-ui.html without receiving an error

Screenshots

[vinit2tiwari]

when will these changes be released? i don't see any release after April 2nd 2023 here
https://mvnrepository.com/artifact/org.springdoc/springdoc-openapi-common