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。

3. jackson-all-1.9.11.jar下载地址http://wiki.fasterxml.com/JacksonDownload

4. 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