SpringMVC的Body参数拦截

忘是亡心i 2021-09-12 01:14 272阅读 0赞

> SpringMVC对出参和入参有非常友好的拓展支持,方便你对数据的输入和输出有更大的执行权，我们如何通过SpringMVC定义的结果做一系列处理呢？

### 入参 ###

RequestBodyAdvice : 针对所有以@RequestBody的参数做处理

参考案例 : JsonViewRequestBodyAdvice

public class JsonViewRequestBodyAdvice extends RequestBodyAdviceAdapter {
    
        /**
         * 这里是一个前置拦截匹配操作,其实就是告诉你满足为true的才会执行下面的beforeBodyRead方法,这里可以定义自己业务相关的拦截匹配
         * @param methodParameter
         * @param targetType
         * @param converterType
         * @return
         */
        @Override
        public boolean supports(MethodParameter methodParameter, Type targetType,
                Class<? extends HttpMessageConverter<?>> converterType) {
                   
            return (AbstractJackson2HttpMessageConverter.class.isAssignableFrom(converterType) &&
                    methodParameter.getParameterAnnotation(JsonView.class) != null);
        }
    
            // 这里就是具体的前置操作了... 下面的例子就是查找这个入参方法是否有@JsonView修饰
        @Override
        public HttpInputMessage beforeBodyRead(HttpInputMessage inputMessage, MethodParameter methodParameter,
                Type targetType, Class<? extends HttpMessageConverter<?>> selectedConverterType) throws IOException {
    
            JsonView annotation = methodParameter.getParameterAnnotation(JsonView.class);
            Class<?>[] classes = annotation.value();
            if (classes.length != 1) {
                throw new IllegalArgumentException(
                        "@JsonView only supported for request body advice with exactly 1 class argument: " + methodParameter);
            }
            return new MappingJacksonInputMessage(inputMessage.getBody(), inputMessage.getHeaders(), classes[0]);
        }
    
    }

### 出参 ###

ResponseBodyAdvice: 针对所有以@ResponseBody的参数做处理

参考案例:

@ControllerAdvice
    public class LogResponseBodyAdvice implements ResponseBodyAdvice {
     
        /**
         *
         * @param returnType
         * @param converterType
         * @return
         */
        @Override
        public boolean supports(MethodParameter returnType, Class converterType) {
            return true;
        }
    
        @Override
        public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
           // 做任何事情 body 就是返回的结果对象,没有处理之前
            return body; 
        }
    }

## 注意事项 ##

自定义的处理对象类上必须得加上@ControllerAdvice注解!  
为什么?  
源码中`RequestMappingHandlerAdapter`类在执行`initControllerAdviceCache()`做初始化的时候会执行一个

List<ControllerAdviceBean> beans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
    AnnotationAwareOrderComparator.sort(beans);

而ControllerAdviceBean.findAnnotatedBeans方法会查找类上有ControllerAdvice注解的类才会加入到处理当中..

public static List<ControllerAdviceBean> findAnnotatedBeans(ApplicationContext applicationContext) {
            List<ControllerAdviceBean> beans = new ArrayList<ControllerAdviceBean>();
            for (String name : BeanFactoryUtils.beanNamesForTypeIncludingAncestors(applicationContext, Object.class)) {
                if (applicationContext.findAnnotationOnBean(name, ControllerAdvice.class) != null) {
                    beans.add(new ControllerAdviceBean(name, applicationContext));
                }
            }
            return beans;
        }

所以大家可以根据自己的需要,定义结果的入参和出参结果做一些特殊处理.....