# 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](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](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](https://github.com/waylau/RestDemo/tree/master/jersey-demo3-json)