使用Struts2+Gson+JQuery实现异步请求JSON对象
GSON是Google公司的Java对象序列化成JSON的插件
下载地址：http://code.google.com/p/google-gson/downloads/list
下载下来以后：把gson-1.4.jar这个jar文件加到工程里。
Action的使用方式是：

package test.gson;import java.io.PrintWriter;import javax.servlet.http.HttpServletResponse;import org.apache.struts2.ServletActionContext;import com.google.gson.Gson;import com.opensymphony.xwork2.ActionSupport;public class TestGson extends ActionSupport {private static final long serialVersionUID = 1L;private Users user;public Users getUser() {return user;}public void setUser(Users user) {this.user = user;}@Overridepublic String execute() throws Exception {user = new Users();user.setId(10000);user.setUserName("zhangsan");user.setPwd("000000");user.setEmail("zhangsan@sina.com");Gson g  = new Gson();String json = g.toJson(user);HttpServletResponse response = ServletActionContext.getResponse();response.setContentType("application/json;charset=utf-8");response.setHeader("Cache-Control","no-cache");PrintWriter pw = response.getWriter();pw.print(json);pw.flush();pw.close();return null;}}

其中response.setContentType("application/json;charset=utf-8");是最重要的
一定要把ContentType设置成application/json形式
struts.xml:

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd"><struts><package name="jsons" extends="struts-default" namespace="/"><action name="testGson" class="test.gson.TestGson"></action></package></struts>

Gson其实可以用在所有的Javaweb工程了，不一定是Struts2