SpringMVC自定义MethodReturnValueHandler学习笔记

1. 编写HandlerMethodReturnValueHandler实现类

   public class PropertiesHandlerMethodReturnValueHandler implements  HandlerMethodReturnValueHandler {
         
         
       @Override
       public boolean supportsReturnType(MethodParameter returnType) {
         
         
           // 判断方法的返回值，是否为Properties
           Class<?> returnType1 = returnType.getMethod().getReturnType();
           return Properties.class.isAssignableFrom(returnType1);
       }
       @Override
       public void handleReturnValue(Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
         
         
           // 告知 spring mvc当前请求已经处理完毕，参考RequestResponseBodyMethodProcessor.handleReturnValue
           mavContainer.setRequestHandled(true); 
           Properties properties = (Properties) returnValue ;
           PropertiesHttpMessageConverter converter = new PropertiesHttpMessageConverter() ;
           ServletWebRequest servletWebRequest = (ServletWebRequest) webRequest ;
           HttpServletRequest request = servletWebRequest.getRequest();
           String contentType = request.getHeader("Content-Type");
           MediaType mediaType = MediaType.parseMediaType(contentType);
           //获取Servlet Response对象
           HttpServletResponse response = servletWebRequest.getResponse() ;
           HttpOutputMessage message = new ServletServerHttpResponse(response) ;
           converter.write(properties, mediaType, message);
       }
   }
   

2. 编写配置类将HandlerMethodReturnValueHandler注册到RequestMappingHandlerAdapter中

   @Configuration
   public class RestWebMvcConfigurer implements WebMvcConfigurer {
         
         
       @Autowired
       private RequestMappingHandlerAdapter requestMappingHandlerAdapter ;
       @PostConstruct
       public void init(){
         
         
           // 注册PropertiesHandlerMethodReturnValueHandler
           List<HandlerMethodReturnValueHandler> handlers =
                   requestMappingHandlerAdapter.getReturnValueHandlers();
           List<HandlerMethodReturnValueHandler> newHandlers = new ArrayList<>(handlers.size() + 1) ;
           newHandlers.add(new PropertiesHandlerMethodReturnValueHandler());
           newHandlers.addAll(handlers) ;
           // 重置Handler对象集合
           requestMappingHandlerAdapter.setReturnValueHandlers(newHandlers);
       }
   }
   

3. 编写Controller业务方法，注意这里无@ResponseBody注解,使用@Controller而不是@RestController

   @Controller
   public class PropertiesRestController {
         
         
       @PostMapping(value = "/add/props",
           consumes = "text/properties;charset=UTF-8"/*,produces = "text/properties"*/)
       public Properties addProp(/*@RequestBody*/ Properties properties){
         
         
           log.info("====> prop : {}" , properties);
           return properties ;
       }
   }
   

4. 使用PostMan发送请求，将Header的Content-Type设置为text/properties

   4.1 header内容
       Content-Type设置为text/properties
   4.1 body内容
       username=yicj
       addr=北京