# 用Jersey構建RESTful服務3--JAVA對象轉成JSON輸出 ## 一、 總體說明 XML和JSON 是最為常用的數據交換格式。本例子演示如何將java對象，轉成JSON輸出。 ## 二、流程 1. 在上文項目中， 在“com.waylau.rest.resources.UserResource“中增加代碼，代碼如下： ``` @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 說明輸出的是JSON格式 2. 運行項目，瀏覽器輸入[http://localhost:8089/RestDemo/rest/users/getUserJson](http://localhost:8089/RestDemo/rest/users/getUserJson) 期望獲取到json的數據，此時，項目報錯 ``` 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) ```  此時，需要獲取json轉換包的支持 。 可以由多種方式實現：MOXy、JSON-P、Jackson、Jettison等，本例為Jackson。 3. jackson-all-1.9.11.jar 下載地址http://wiki.fasterxml.com/JacksonDownload 4. 項目中引入jackson-all-1.9.11.jar 5. 在“com.waylau.rest”目錄下創建RestApplication.java ``` package com.waylau.rest; import org.codehaus.jackson.jaxrs.JacksonJsonProvider; import org.glassfish.jersey.filter.LoggingFilter; import org.glassfish.jersey.server.ResourceConfig; /** * 應用 * @author waylau.com * 2014-3-18 */ public class RestApplication extends ResourceConfig { public RestApplication() { //服務類所在的包路徑 packages("com.waylau.rest.resources"); //注冊JSON轉換器 register(JacksonJsonProvider.class); } } ``` 6. 修改web.xml，初始化從RestApplicaton進入應用，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. 運行項目，再次訪問[http://localhost:8089/RestDemo/rest/users/getUserJson](http://localhost:8089/RestDemo/rest/users/getUserJson) 即可輸出JSON文本  **本章源碼**：[https://github.com/waylau/RestDemo/tree/master/jersey-demo3-json](https://github.com/waylau/RestDemo/tree/master/jersey-demo3-json)