Spring Mono Object wrapped by ResponseEntity cannot be passed correctly by mvc framework

Affects: 5.3.x

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Please refer to this disscusion for more detailed information. In function ResponseBodyEmitterReturnValueHandler.supportsReturnType, it failed to recognize the correct type when a controller returns an object having a Mono object wrapped by ResponseEntity. However, the parameter HandlerMethod.ReturnValueMethodParameter actually has an attribute returnValue containing enough information.

I wonder if there's a way taking return value into consideration. I tried to fetch the actual return value at runtime, but the subclass HandlerMethod.ReturnValueMethodParameter is protected, so the type cannot be converted from MethodParameter to HandlerMethod.ReturnValueMethodParameter.

Comment From: rstoyanchev

Please, don't create additional issues for existing issues.