package com.json;

public class User {

    String username;

    String password;

    public String getUsername() {

        return username;

    }

    public void setUsername(String username) {

        this.username = username;

    }

    public String getPassword() {

        return password;

    }

    public void setPassword(String password) {

        this.password = password;

    }

}

package com.json;

import java.io.IOException;

import java.io.PrintWriter;

import java.util.ArrayList;

import java.util.List;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import net.sf.json.JSONArray;

public class TestJson extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

           doPost(request,response);

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        response.setContentType("text/html");

　　　　 String str= =request.getParameter("name");//得到ajax传递过来的paramater

        PrintWriter out = response.getWriter();

        List list = new ArrayList();//传递List

        Map m=new HashMap();//传递Map    

        User u1=new User();

        u1.setUsername("zah");

        u1.setPassword("123");

        User u2=new User();

        u2.setUsername("ztf");

        u2.setPassword("456");  

        list.add(u1); //添加User对象

        list.add(u2);     //添加User对象  

        m.put("u1", u1);

        m.put("u2", u2);   

       JSONArray jsonArray2 = JSONArray.fromObject( list );

       //把java数组转化成转化成json对象

       JSONObject jo=JSONObject.fromObject(m);

       //转化Map对象

       out.print(jsonArray2);//返给ajax请求

       out.print(jo);//返给ajax请求

    }

}

<script type="text/javascript" src="js/jquery.js"></script>

<script type="text/javascript">

     function test(){

         $.ajax({

                type:"POST", //请求方式

                url:"testjson", //请求路径

                cache: false,

                data:"name=zah",  //传参

                dataType: 'json',   //返回值类型

                success:function(json){

                    alert(json[0].username+" " json[0].password);    //弹出返回过来的List对象

                   }

                });

      }

</script>

<body>

   <input type="button" name="b" value="测试" onclick=test()>

</body>

success:function(json){

    alert(json.u1.username)

}