@RequestBody对象为空，异常Required request body is missing

1.异常

org.springframework.http.converter.HttpMessageNotReadableException: Required request body is missing

2.问题复现：

@RequestMapping(value = "/somewhere", method = POST)
public SomeResponse someHandler(@RequestBody XXXDTO xxxDTO) { ... }

当入参DTO对象为空时，

@RequestBody对应http请求body,当请求body为空时，异常！
org.springframework.http.converter.HttpMessageNotReadableException: Required request body is missing: public com.rpc.common.Result<com.rpc.common.dto.PageDto<com.order.dto.OrderListDTO>> com.gateway.controller.OrderController.listOrder(com.*.*.order.dto.ListOrderPageDTO)
        at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.readWithMessageConverters(RequestResponseBodyMethodProcessor.java:154)
        at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.resolveArgument(RequestResponseBodyMethodProcessor.java:128)
        at org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:121)
        at org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:158)
        at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:128)
        at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:97)
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
        at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967)
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901)
        at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
        at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
        at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
        at org.springframework.boot.web.filter.ApplicationContextHeaderFilter.doFilterInternal(ApplicationContextHeaderFilter.java:55)
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)

 @Override
     protected <T> Object readWithMessageConverters(NativeWebRequest webRequest, MethodParameter parameter,
             Type paramType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {

         HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);
         ServletServerHttpRequest inputMessage = new ServletServerHttpRequest(servletRequest);

         Object arg = readWithMessageConverters(inputMessage, parameter, paramType);
         if (arg == null) {
             if (checkRequired(parameter)) {
                 throw new HttpMessageNotReadableException("Required request body is missing: " +
                         parameter.getMethod().toGenericString());
             }
         }
         return arg;
     }

     protected boolean checkRequired(MethodParameter parameter) {
         return (parameter.getParameterAnnotation(RequestBody.class).required() && !parameter.isOptional());
     }

看上图，最终是RequestBody注解的required属性。!parameter.isOptional()代表是否支持null,如果参数类型支持null,则是false,最终不用校验required.

 public @interface RequestBody {

     /**
      * Whether body content is required.
      * <p>Default is {@code true}, leading to an exception thrown in case
      * there is no body content. Switch this to {@code false} if you prefer
      * {@code null} to be passed when the body content is {@code null}.
      * @since 3.2
      */
     boolean required() default true;

 }

看上图，默认是true.我们只需要@RequestBody （required=false）

3.解决方案：

1）@RequestBody （required=false）

2) 不要让DTO对象为空