用Jersey构建RESTful服务3--JAVA对象转成JSON输出

#一、总体说明

XML和JSON 是最为常用的数据交换格式。本例子演示如何将java对象，转成JSON输出。

#二、流程

1.在上文项目中，在“com.waylau.rest.resources.UserResource“中增加代码，代码如下：

	@GET    
	@Path("/getUserJson")    
	@Produces(MediaType.APPLICATION_JSON)    
	public User getUserJson() {    
	 User user  = new User();    
	 user.setAge("27");    
	 user.setUserId("005");    
	 user.setUserName("Fmand");    
	 return user;    
	}   

MediaType.APPLICATION_JSON 说明输出的是JSON格式

2,运行项目，浏览器输入http://localhost:8089/RestDemo/rest/users/getUserJson 期望获取到json的数据，此时，项目报错

	org.glassfish.jersey.message.internal.MessageBodyProviderNotFoundException: MessageBodyWriter not found for media type=application/json, type=class com.waylau.rest.bean.User, genericType=class com.waylau.rest.bean.User.  
	    at org.glassfish.jersey.message.internal.WriterInterceptorExecutor$TerminalWriterInterceptor.aroundWriteTo(WriterInterceptorExecutor.java:247)  
	    at org.glassfish.jersey.message.internal.WriterInterceptorExecutor.proceed(WriterInterceptorExecutor.java:162)  
	    at org.glassfish.jersey.filter.LoggingFilter.aroundWriteTo(LoggingFilter.java:293)  
	    at org.glassfish.jersey.message.internal.WriterInterceptorExecutor.proceed(WriterInterceptorExecutor.java:162)  
	    at org.glassfish.jersey.server.internal.JsonWithPaddingInterceptor.aroundWriteTo(JsonWithPaddingInterceptor.java:103)  
	    at org.glassfish.jersey.message.internal.WriterInterceptorExecutor.proceed(WriterInterceptorExecutor.java:162)  
	    at org.glassfish.jersey.server.internal.MappableExceptionWrapperInterceptor.aroundWriteTo(MappableExceptionWrapperInterceptor.java:88)  
	    at org.glassfish.jersey.message.internal.WriterInterceptorExecutor.proceed(WriterInterceptorExecutor.java:162)  
	    at org.glassfish.jersey.message.internal.MessageBodyFactory.writeTo(MessageBodyFactory.java:1154)  
	    at org.glassfish.jersey.server.ServerRuntime$Responder.writeResponse(ServerRuntime.java:571)  
	    at org.glassfish.jersey.server.ServerRuntime$Responder.processResponse(ServerRuntime.java:378)  
	    at org.glassfish.jersey.server.ServerRuntime$Responder.process(ServerRuntime.java:368)  
	    at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:262)  

此时，需要获取json转换包的支持。可以由多种方式实现：MOXy、JSON-P、Jackson、Jettison等，本例为Jackson。

1. jackson-all-1.9.11.jar 下载地址http://wiki.fasterxml.com/JacksonDownload
1. 项目中引入jackson-all-1.9.11.jar
5.在“com.waylau.rest”目录下创建RestApplication.java

package com.waylau.rest;  
  
import org.codehaus.jackson.jaxrs.JacksonJsonProvider;  
import org.glassfish.jersey.filter.LoggingFilter;  
import org.glassfish.jersey.server.ResourceConfig;  
   
/** 
 * 应用 
 * @author waylau.com 
 * 2014-3-18 
 */  
public class RestApplication extends ResourceConfig {  
    public RestApplication() {  
   
     //服务类所在的包路径  
     packages("com.waylau.rest.resources");  
     //注册JSON转换器  
     register(JacksonJsonProvider.class);  
   
    }  
}  

6.修改web.xml，初始化从RestApplicaton进入应用，如下：

<servlet>    
     <servlet-name>Way REST Service</servlet-name>  
     <servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>  
      <init-param>  
           <param-name>javax.ws.rs.Application</param-name>  
           <param-value>com.waylau.rest.RestApplication</param-value>  
       </init-param>  
       
    <load-on-startup>1</load-on-startup>  
  </servlet>  
    
  <servlet-mapping>  
    <servlet-name>Way REST Service</servlet-name>  
    <url-pattern>/rest/*</url-pattern>  
  </servlet-mapping>  

7.运行项目，再次访问http://localhost:8089/RestDemo/rest/users/getUserJson 即可输出JSON文本

本章源码：https://github.com/waylau/RestDemo/tree/master/jersey-demo3-json

Way Lau

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