掌握@ControllerAdvice配合RequestBodyAdvice/ResponseBodyAdvice使用，让你的选择不仅仅只有拦截器【享学Spring MVC】(下)

@ResponseBody
@GetMapping("/test/responsebody")
@JsonView(Simple.class)
public User testResponseBodyAdvice() {
    User user = new User();
    user.setId(1L);
    user.setName("fsx");
    user.setAge(18);
    return user;
}

// @since 4.2  请注意：它的访问权限是default哦
class RequestResponseBodyAdviceChain implements RequestBodyAdvice, ResponseBodyAdvice<Object> {
  //它持有所有的，记住是所有的advice们
  private final List<Object> requestBodyAdvice = new ArrayList<>(4);
  private final List<Object> responseBodyAdvice = new ArrayList<>(4);
  // 可以看到这是个通用的方法。内来进行区分存储的   getAdviceByType这个区分方法可以看一下
  // 兼容到了ControllerAdviceBean以及beanType本身
  public RequestResponseBodyAdviceChain(@Nullable List<Object> requestResponseBodyAdvice) {
    this.requestBodyAdvice.addAll(getAdviceByType(requestResponseBodyAdvice, RequestBodyAdvice.class));
    this.responseBodyAdvice.addAll(getAdviceByType(requestResponseBodyAdvice, ResponseBodyAdvice.class));
  }
  @Override
  public boolean supports(MethodParameter param, Type type, Class<? extends HttpMessageConverter<?>> converterType) {
    throw new UnsupportedOperationException("Not implemented");
  }
  @Override
  public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
    throw new UnsupportedOperationException("Not implemented");
  }
  // 可以看到最终都是委托给具体的Advice去执行的（supports方法）
  // 特点：符合条件的所有的`Advice`都会顺序的、依次的执行
  @Override
  public HttpInputMessage beforeBodyRead(HttpInputMessage request, MethodParameter parameter, Type targetType, Class<? extends HttpMessageConverter<?>> converterType) throws IOException {
    for (RequestBodyAdvice advice : getMatchingAdvice(parameter, RequestBodyAdvice.class)) {
      if (advice.supports(parameter, targetType, converterType)) {
        request = advice.beforeBodyRead(request, parameter, targetType, converterType);
      }
    }
    return request;
  }
  ... // 其余方法略。处理逻辑同上顺序执行。
  // 最重要的是如下这个getMatchingAdvice()匹配方法
  private <A> List<A> getMatchingAdvice(MethodParameter parameter, Class<? extends A> adviceType) {
    // 简单的说你想要的是Request的还是Response的List呢？
    List<Object> availableAdvice = getAdvice(adviceType);
    if (CollectionUtils.isEmpty(availableAdvice)) {
      return Collections.emptyList();
    }
    List<A> result = new ArrayList<>(availableAdvice.size());
    for (Object advice : availableAdvice) {
      if (advice instanceof ControllerAdviceBean) {
        ControllerAdviceBean adviceBean = (ControllerAdviceBean) advice;
        // 这里面会调用beanTypePredicate.test(beanType)方法
        // 也就是根据basePackages等等判断此advice是否是否要作用在本类上
        if (!adviceBean.isApplicableToBeanType(parameter.getContainingClass())) {
          continue;
        }
        advice = adviceBean.resolveBean();
      }
      // 当前的advice若是满足类型要求的，那就添加进去  最终执行切面操作
      if (adviceType.isAssignableFrom(advice.getClass())) {
        result.add((A) advice);
      }
    }
    return result;
  }
}

AbstractMessageConverterMethodArgumentResolver（一般实际为RequestResponseBodyMethodProcessor）：
  // 唯一构造函数，指定所有的advices
  public AbstractMessageConverterMethodArgumentResolver(List<HttpMessageConverter<?>> converters, @Nullable List<Object> requestResponseBodyAdvice) {
    Assert.notEmpty(converters, "'messageConverters' must not be empty");
    this.messageConverters = converters;
    this.allSupportedMediaTypes = getAllSupportedMediaTypes(converters);
    this.advice = new RequestResponseBodyAdviceChain(requestResponseBodyAdvice);
  }