Spring 学习 - 对结果进行处理

心已赠人 2023-07-07 08:46 64阅读 0赞

## 前言 ##

在工作中，我们可能需要封装一下返回值

比如将返回值封装为

{ 
      code: "200",
      data: "www"
    }

## 演示 ##

自定义注解

@Target({ ElementType.TYPE, ElementType.METHOD})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface ResponseData { 
    }

返回www，等待上层封装

@RestController
    public class TestController { 
    
        @GetMapping("test")
        @ResponseData		// 自定义注解
        public String test(){ 
            return "www";
        }
    }

自定义处理器 HandlerMethodReturnValueHandler

public class MyHandlerMethodReturnValueHandler implements HandlerMethodReturnValueHandler { 
        private final RequestResponseBodyMethodProcessor target;
    
        public MyHandlerMethodReturnValueHandler(RequestResponseBodyMethodProcessor target) { 
            this.target = target;
        }
    
        @Override
        public boolean supportsReturnType(MethodParameter methodParameter) { 
            System.out.println("TestReturnValueHandler:supportsReturnType");
            // 是否为自定义注解，以及默认的 ResponseData
            return methodParameter.hasMethodAnnotation(ResponseData.class)||
                    methodParameter.hasMethodAnnotation(ResponseBody.class);
        }
    
        @Override
        public void handleReturnValue(Object o, MethodParameter methodParameter,
                                      ModelAndViewContainer modelAndViewContainer,
                                      NativeWebRequest nativeWebRequest) throws Exception { 
            System.out.println("TestReturnValueHandler:handleReturnValue");
            if(methodParameter.hasMethodAnnotation(ResponseData.class)){ 
                //使用了自定义注解 ResponseData，那么对返回值进行封装
                Map<String,Object> res = new HashMap<>();
                res.put("code","200");
                res.put("data",o);
    						target.handleReturnValue
      							(res,methodParameter,modelAndViewContainer,nativeWebRequest);
            } else { 
                // 其他情况，默认
    						target.handleReturnValue(
             	 		o,methodParameter,modelAndViewContainer,nativeWebRequest);
            }
        }
    
    }

初始化切面，主要是为了在启动时，替换原来的类为自己的类

`其实为什么这么做是因为spring-mvc中array然后往里加，你自定义的类正常是排不到前面的，也就是系统类已经处理了，就轮不到你了`

@Configuration
    public class InitializingAdvice implements InitializingBean { 
    
        @Autowired
        private RequestMappingHandlerAdapter adapter;
    
        @Override
        public void afterPropertiesSet() throws Exception { 
            List<HandlerMethodReturnValueHandler> returnValueHandlers = adapter.getReturnValueHandlers();
            List<HandlerMethodReturnValueHandler> handlers = new ArrayList(returnValueHandlers);
            this.decorateHandlers(handlers);
            adapter.setReturnValueHandlers(handlers);;
        }
    
    
        private void decorateHandlers(List<HandlerMethodReturnValueHandler> handlers) { 
            for (HandlerMethodReturnValueHandler handler : handlers) { 
                if (handler instanceof RequestResponseBodyMethodProcessor) { 
                    MyHandlerMethodReturnValueHandler decorator =
                      new MyHandlerMethodReturnValueHandler(
                            (RequestResponseBodyMethodProcessor) handler);
                    int index = handlers.indexOf(handler);
                    handlers.set(index, decorator);
                    break;
                }
            }
        }
    }

启动

@SpringBootApplication
    public class SpringbootDemoApplication { 
    
        public static void main(String[] args) { 
            SpringApplication.run(SpringbootDemoApplication.class, args);
        }
    
    }

访问：http://localhost:8080/test

{ 
      code: "200",
      data: "www"
    }