SSM框架之@ResponseBody和@RequestBody的区别及HttpMessageConverter的作用

一、@ResponseBody

@ResponseBody作用于方法上，将返回结果直接以Json等格式返回，直接封装到response对象的Body中，不经过SpringMVC的视图解析器。一般用于前后端分离的项目，或者Ajax等异步请求。

@ResponseBody
public Student getStudent(Integer id){
      Student student = sstudentService.getStudent(id);
　　　　return student;
}
//前端得到的Json数据：
'{"id":"201541030102","name":"刘聪"，"sex":"男"}'

二、@RequestBody

@RequestBody作用方法的形参，将前端传来的Json等格式的数据封装到javabean中。它会直接读取读取Request请求的body部分数据，再使用HttpMessageConverter进行解析。

//前端传来的的Json数据：
'{"id":"201541030102","name":"刘聪"，"sex":"男"}'

@ResponseBody
public Integer setStudent(@ResponseBody Student student){
      Integer total = sstudentService.setStudent(stedent);
　　　　return total;
}

三、HttpMessageConverter

HTTP的请求报文就是一种字符串，在java中会被封装在ServletInputStream流里，我们在从流中获得数据，HTTP的响应报文则是通过ServletOutputStream流进行向外输出的。

获得请求报文的信息实际就是HttpMessageConverter接口通过相应的实现类来解析流中的信息，并转化为Spring中可以使用的Javabean的过程，响应过程相反。

HttpMessageConverter接口源码；

/*
 * Copyright 2002-2010 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.http.converter;

import java.io.IOException;
import java.util.List;

import org.springframework.http.HttpInputMessage;
import org.springframework.http.HttpOutputMessage;
import org.springframework.http.MediaType;

/**
 * Strategy interface that specifies a converter that can convert from and to HTTP requests and responses.
 *
 * @author Arjen Poutsma
 * @author Juergen Hoeller
 * @since 3.0
 */
public interface HttpMessageConverter<T> {

	/**
	 * Indicates whether the given class can be read by this converter.
	 * @param clazz the class to test for readability
	 * @param mediaType the media type to read, can be {@code null} if not specified.
	 * Typically the value of a {@code Content-Type} header.
	 * @return {@code true} if readable; {@code false} otherwise
	 */
	boolean canRead(Class<?> clazz, MediaType mediaType);

	/**
	 * Indicates whether the given class can be written by this converter.
	 * @param clazz the class to test for writability
	 * @param mediaType the media type to write, can be {@code null} if not specified.
	 * Typically the value of an {@code Accept} header.
	 * @return {@code true} if writable; {@code false} otherwise
	 */
	boolean canWrite(Class<?> clazz, MediaType mediaType);

	/**
	 * Return the list of {@link MediaType} objects supported by this converter.
	 * @return the list of supported media types
	 */
	List<MediaType> getSupportedMediaTypes();

	/**
	 * Read an object of the given type form the given input message, and returns it.
	 * @param clazz the type of object to return. This type must have previously been passed to the
	 * {@link #canRead canRead} method of this interface, which must have returned {@code true}.
	 * @param inputMessage the HTTP input message to read from
	 * @return the converted object
	 * @throws IOException in case of I/O errors
	 * @throws HttpMessageNotReadableException in case of conversion errors
	 */
	T read(Class<? extends T> clazz, HttpInputMessage inputMessage)
			throws IOException, HttpMessageNotReadableException;

	/**
	 * Write an given object to the given output message.
	 * @param t the object to write to the output message. The type of this object must have previously been
	 * passed to the {@link #canWrite canWrite} method of this interface, which must have returned {@code true}.
	 * @param contentType the content type to use when writing. May be {@code null} to indicate that the
	 * default content type of the converter must be used. If not {@code null}, this media type must have
	 * previously been passed to the {@link #canWrite canWrite} method of this interface, which must have
	 * returned {@code true}.
	 * @param outputMessage the message to write to
	 * @throws IOException in case of I/O errors
	 * @throws HttpMessageNotWritableException in case of conversion errors
	 */
	void write(T t, MediaType contentType, HttpOutputMessage outputMessage)
			throws IOException, HttpMessageNotWritableException;

}

一些相关的实现类