SpringMVC中使用@RequestBody,@ResponseBody注解实现Java对象和XML/JSON数据自动转换（下）

上一篇分析了Spring中是如何通过使用@ResponseBody注解，实现自动转换Java对象为XML,JSON数据到Reponse中。

接下来看看如果request中包含了XML或者JSON数据，反过来，如何来通过@RequestBody注解来自动转换为Java对象。

配合@RequestBody注解，以及HTTP Request Header中的Content-Type属性，HTTP Request Body中包含的XML或者JSON数据可以自动被转换成对应的Java对象。

1）首先在controller中添加handlermapping。

	/**
	 * 根据request header中的Content-Type自动转换XML/JSON->EmployeeX对象
	 * 根据request header中的Accept自动选择返回XML or JSON
	 */
	@RequestMapping(method=RequestMethod.POST)
	@ResponseBody
	public EmployeeServiceResponse createEmployee(@RequestBody EmployeeX employee) {
		logger.debug("creating a employee:[{}]", employee);
		return new EmployeeServiceResponse(0, "");
	}

package learning.webapp.model;

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class EmployeeServiceResponse {
	private Integer errcode;
	private String errmsg;

	public EmployeeServiceResponse() {
	}
	
	public EmployeeServiceResponse(Integer errcode, String errmsg) {
		this.errcode = errcode;
		this.errmsg = errmsg;
	}
		
	public Integer getErrcode() {
		return errcode;
	}

	public void setErrcode(Integer errcode) {
		this.errcode = errcode;
	}

	public String getErrmsg() {
		return errmsg;
	}

	public void setErrmsg(String errmsg) {
		this.errmsg = errmsg;
	}
}

2）运行以下两个测试函数

	@Test
	public void testJsonRequestResponse() throws IOException, URISyntaxException {
		String url = "http://localhost:8080/employees";
		HttpHeaders requestHeaders = new HttpHeaders();
		requestHeaders.set("Accept", "application/json");
		requestHeaders.set("Content-Type", "application/json");
		
		String jsonStr = "{\"name\":\"Jack\",\"salary\":16000}";

		RestTemplate restTemplate = new RestTemplate();
		HttpEntity httpEntity = new HttpEntity(jsonStr, requestHeaders);
		String jsonData = restTemplate.postForObject(url, httpEntity, String.class);

		System.out.println(jsonData);
	}
	
	@Test
	public void testXmlRequestResponse() throws IOException, URISyntaxException {
		String url = "http://localhost:8080/employees";
		HttpHeaders requestHeaders = new HttpHeaders();
		requestHeaders.set("Accept", "application/xml");
		requestHeaders.set("Content-Type", "application/xml");
		
		String xmlStr = "Jack16000";

		RestTemplate restTemplate = new RestTemplate();
		HttpEntity httpEntity = new HttpEntity(xmlStr, requestHeaders);
		String xmlData = restTemplate.postForObject(url, httpEntity, String.class);

		System.out.println(xmlData);
	}

3）我们甚至可以任意组合请求和应答中的XML/JSON。比如Request=XML，Response=JSON

	@Test
	public void testXmlRequestJsonResponse() throws IOException, URISyntaxException {
		String url = "http://localhost:8080/employees";
		HttpHeaders requestHeaders = new HttpHeaders();
		requestHeaders.set("Accept", "application/json");
		requestHeaders.set("Content-Type", "application/xml");
		
		String xmlStr = "Jack16000";

		RestTemplate restTemplate = new RestTemplate();
		HttpEntity httpEntity = new HttpEntity(xmlStr, requestHeaders);
		String jsonData = restTemplate.postForObject(url, httpEntity, String.class);

		System.out.println(jsonData);
	}

类似上一篇中的分析，最关键的处理在AbstractMessageConverterMethodArgumentResolver.readWithMessageConverters(）。它会根据request header中的Content-Type属性来选择合适的message converter.

---------------------

以下引用自参考资料1：

如果不想使用中默认的RequestMappingHandlerAdapter的话，我们可以在重新定义这个bean，spring会覆盖掉默认的RequestMappingHandlerAdapter。

为何会覆盖，请参考博客：http://www.cnblogs.com/fangjian0423/p/spring-Ordered-interface.html

    <bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
  <property name="messageConverters">
    <list>
      <bean class="org.springframework.http.converter.ByteArrayHttpMessageConverter"/>
      <bean class="org.springframework.http.converter.StringHttpMessageConverter"/>
      <bean class="org.springframework.http.converter.ResourceHttpMessageConverter"/>
    list>
  property>
bean>

或者如果只想换messageConverters的话。

<mvc:annotation-driven>
  <mvc:message-converters>
    <bean class="org.example.MyHttpMessageConverter"/>
    <bean class="org.example.MyOtherHttpMessageConverter"/>
  mvc:message-converters>
mvc:annotation-driven>

[参考资料]
1）http://www.cnblogs.com/fangjian0423/p/springMVC-xml-json-convert.html
2）http://my.oschina.net/lichhao/blog/172562