RequestBodyAdvice和ResponseBodyAdvice

RequestBodyAdvice和ResponseBodyAdvice

这是spring 4.2新加的两个接口，这两个接口有些什么作用呢？先看看这两个接口

RequestBodyAdvice

public interface RequestBodyAdvice {

	boolean supports(MethodParameter methodParameter, Type targetType,
			Class<? extends HttpMessageConverter<?>> converterType);

	Object handleEmptyBody(Object body, HttpInputMessage inputMessage, MethodParameter parameter,
			Type targetType, Class<? extends HttpMessageConverter<?>> converterType);

	HttpInputMessage beforeBodyRead(HttpInputMessage inputMessage, MethodParameter parameter,
			Type targetType, Class<? extends HttpMessageConverter<?>> converterType) throws IOException;

	Object afterBodyRead(Object body, HttpInputMessage inputMessage, MethodParameter parameter,
			Type targetType, Class<? extends HttpMessageConverter<?>> converterType);

}

查看一下谁调用了这个接口的这些方法，可以看到AbstractMessageConverterMethodArgumentResolver的readWithMessageConverters()方法调用了这个接口的方法。

//代码片段
for (HttpMessageConverter<?> converter : this.messageConverters) {
			Class<HttpMessageConverter<?>> converterType = (Class<HttpMessageConverter<?>>) converter.getClass();
			if (converter instanceof GenericHttpMessageConverter) {
				GenericHttpMessageConverter<?> genericConverter = (GenericHttpMessageConverter<?>) converter;
				if (genericConverter.canRead(targetType, contextClass, contentType)) {
					if (logger.isDebugEnabled()) {
						logger.debug("Read [" + targetType + "] as \"" + contentType + "\" with [" + converter + "]");
					}
					if (inputMessage.getBody() != null) {
						inputMessage = getAdvice().beforeBodyRead(inputMessage, param, targetType, converterType);
						body = genericConverter.read(targetType, contextClass, inputMessage);
						body = getAdvice().afterBodyRead(body, inputMessage, param, targetType, converterType);
					}
					else {
						body = null;
						body = getAdvice().handleEmptyBody(body, inputMessage, param, targetType, converterType);
					}
					break;
				}
			}

可以看到这接口的方法，主要是在HttpMessageConverter处理request body的前后做一些处理，和body为空的时候做处理。
而AbstractMessageConverterMethodArgumentResolver的实现类有
HttpEntityMethodProcessor(处理controller的方法参数是HttpEntity或RequestEntity的)、
RequestResponseBodyMethodProcessor(处理方法参数有@RequestBoyd的)、
RequestPartMethodArgumentResolver(处理方法参数是@RequestPart或MultipartFile,javax.servlet.http.Part)。

从这个可以看出，我们可以在使用这些HandlerMethodArgumentResolver的时候，我们能对request body进行前处理，和解析后处理。

RequestBodyAdvice怎么用

首先一个实现类，实现RequestBodyAdvice，后在类上加上注解@ControllerAdvice，比如有些请求的参数需要做加密处理，可以在此将json串解密处理，在处理

ResponseBodyAdvice

public interface ResponseBodyAdvice<T> {


boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType);


T beforeBodyWrite(T body, MethodParameter returnType, MediaType selectedContentType,
		Class<? extends HttpMessageConverter<?>> selectedConverterType,
		ServerHttpRequest request, ServerHttpResponse response);

}

此可以对@ResponseBody的返回结果在输出到响应之前做处理