RequestBodyAdvice和ResponseBodyAdvice

缺乏、安全感 2022-09-15 12:26 134阅读 0赞

在项目中我们往往需要对请求参数在其被Controller层接收前和响应回客户端前做一些公共的操作，比如参数过滤、解密、加密，验签等操作。SpringMVC为我们提供了RequestBodyAdvice和ResponseBodyAdvice这两个接口就很方便的帮助我处理了这些问题。相比过滤器和拦截器更灵活。

# RequestBodyAdvice #

package com.lpp.encrytdemo.beans;
    
    /**
     * 在请求体被读取或转换为对象前，允许我们自定义请求。还允许在其被发送给Controller方法之前作为 
     *RequestBody对象或请求体被自定义处理
     * 
     *
     *	这个接口的实现可以在继承RequestMappingHandlerAdapter 或者用ControllerAdvice注解标注的情况下自动被侦测到
     */
    public interface RequestBodyAdvice {
    
    	/**
    	 * 首先调用，以确定是否应用此拦截器.
    	 * @param methodParameter the method parameter
    	 * @param targetType the target type, not necessarily the same as the method
    	 * parameter type, e.g. for {@code HttpEntity<String>}.
    	 * @param converterType 所选的转换器类型
    	 * @return 这个拦截器是否被调用
    	 */
    	boolean supports(MethodParameter methodParameter, Type targetType,
    			Class<? extends HttpMessageConverter<?>> converterType);
    
    	/**
    	 * 在读取和转换请求体之前第二次调用.
    	 * @param inputMessage the request
    	 * @param parameter the target method parameter
    	 * @param targetType the target type, not necessarily the same as the method
    	 * parameter type, e.g. for {@code HttpEntity<String>}.
    	 * @param converterType the converter used to deserialize the body
    	 * @return the input request or a new instance, never {@code null}
    	 */
    	HttpInputMessage beforeBodyRead(HttpInputMessage inputMessage, MethodParameter parameter,
    			Type targetType, Class<? extends HttpMessageConverter<?>> converterType) throws IOException;
    
    	/**
    	 * 请求体转换为Object后第三次(也是最后一次)调用。
    	 * @param body set to the converter Object before the first advice is called
    	 * @param inputMessage the request
    	 * @param parameter the target method parameter
    	 * @param targetType the target type, not necessarily the same as the method
    	 * parameter type, e.g. for {@code HttpEntity<String>}.
    	 * @param converterType the converter used to deserialize the body
    	 * @return the same body or a new instance
    	 */
    	Object afterBodyRead(Object body, HttpInputMessage inputMessage, MethodParameter parameter,
    			Type targetType, Class<? extends HttpMessageConverter<?>> converterType);
    
    	/**
    	 * 如果主体为空，则第二个(也是最后一个)调用。
    	 * @param body usually set to {@code null} before the first advice is called
    	 * @param inputMessage the request
    	 * @param parameter the method parameter
    	 * @param targetType the target type, not necessarily the same as the method
    	 * parameter type, e.g. for {@code HttpEntity<String>}.
    	 * @param converterType the selected converter type
    	 * @return the value to use or {@code null} which may then raise an
    	 * {@code HttpMessageNotReadableException} if the argument is required.
    	 */
    	@Nullable
    	Object handleEmptyBody(@Nullable Object body, HttpInputMessage inputMessage, MethodParameter parameter,
    			Type targetType, Class<? extends HttpMessageConverter<?>> converterType);
    
    
    }

## 调用顺序 ##

>     support->beforeBodyRead->afterBodyRead->Controller方法

## 解释 ##

SpringMVC中RequestResponseBodyAdviceChain类中的beforeBodyRead()方法会在先调用support()方法判断是否需要执行实现RequestBodyAdvice的类，然后可以就执行调用实现类的beforeBodyRead（），最后在请求体转为RequestBody实体类后调用afterBodyRead

# ResponseBodyAdvice #

/**
     *	允许在控制器方法执行之后和消息转换器之前对响应体做自定义
     *
     * 其接口的实现类可以直接被注册到RequestMappingHandlerAdapter和ExceptionHandlerExceptionResolver
     * 或者使用ControllerAdvice注解注册
     */
    public interface ResponseBodyAdvice<T> {
    
    	/**
    	 * 该组件是否支持给定的控制器方法返回类型
    	 * *和所选的{@code HttpMessageConverter}类型。
    	 * @param returnType the return type
    	 * @param converterType the selected converter type
    	 * @return {@code true} if {@link #beforeBodyWrite} should be invoked;
    	 * {@code false} otherwise
    	 */
    	boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType);
    
    	/**
    	 * 在选定消息转换器之后调用消息换器之前调用，也就是要将请求体转为json的时候（通俗讲）
    	 * @param body the body to be written
    	 * @param returnType the return type of the controller method
    	 * @param selectedContentType the content type selected through content negotiation
    	 * @param selectedConverterType the converter type selected to write to the response
    	 * @param request the current request
    	 * @param response the current response
    	 * @return the body that was passed in or a modified (possibly new) instance
    	 */
    	@Nullable
    	T beforeBodyWrite(@Nullable T body, MethodParameter returnType, MediaType selectedContentType,
    			Class<? extends HttpMessageConverter<?>> selectedConverterType,
    			ServerHttpRequest request, ServerHttpResponse response);
    
    }

## 调用顺序 ##

> support->beforeBodyWrite

## 解释 ##

首先通过support判断是否可以改写response，可以则调用beforeBodyWrite进行改写。