ResponseBodyAdvice should ignore non-match type instead throw exception [SPR-17539]

[spring-projects-issues]

abccbaandy opened SPR-17539 and commented

When I use 

public class MyAdvice implements ResponseBodyAdvice<MyVo>

and my response data is

ResponseEntity<AnotherVo>

ResponseBodyAdvice will throw ClassCastException, because we can't use "supports" to check the type. It make type declare in ResponseBodyAdvice interface useless.

 

Currently, there is a workaround, use Object

ResponseBodyAdvice<Object>

and check the type in beforeBodyWrite, like this

@Override
public Object beforeBodyWrite(Object o, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
    if (!(o instanceof MyVo)) {
        return o;
    }
    // do rest things here
}

but it doesn't look like a best practice.

 

update:

after study the source, I found there is a class cast before call beforeBodyWrite

RequestResponseBodyAdviceChain

private <T> Object processBody(@Nullable Object body, MethodParameter returnType, MediaType contentType,
      Class<? extends HttpMessageConverter<?>> converterType,
      ServerHttpRequest request, ServerHttpResponse response) {

   for (ResponseBodyAdvice<?> advice : getMatchingAdvice(returnType, ResponseBodyAdvice.class)) {
      if (advice.supports(returnType, converterType)) {
         body = ((ResponseBodyAdvice<T>) advice).beforeBodyWrite((T) body, returnType,
               contentType, converterType, request, response);
      }
   }
   return body;
}

Can we check body is T before call beforeBodyWrite?

---

Affects: 5.0.9

[spring-projects-issues]

Rossen Stoyanchev commented

ResponseBodyAdvice will throw ClassCastException, because we can't use "supports" to check the type.

You can use the supports method to check. MethodParameter has the generic type information, e.g.:

boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
    Class<?> targetType = ResolvableType.forMethodParameter(returnType).getGeneric(0);
    // ...
}

 

Can we check body is T before call beforeBodyWrite?

Not really. We don't have generic type information for the advice bean at that point.