ajax+json+java

1.首先下载json所以依赖的包， Json-lib 最新版 json-lib-2.3-jdk15.jar，其官方网站是：http://json-lib.sourceforge.net/可以直接download，细心的你会发现其网站页面里面有提示它还需要其他包：
Json-lib requires (at least) the following dependencies in your classpath:
•jakarta commons-lang 2.4
•jakarta commons-beanutils 1.7.0
•jakarta commons-collections 3.2
•jakarta commons-logging 1.1.1
•ezmorph 1.0.6
下载地址分别是：
http://commons.apache.org/lang/
http://commons.apache.org/beanutils/
http://commons.apache.org/collections/
http://commons.apache.org/logging/
http://ezmorph.sourceforge.net/

2.首先先见一个小web项目
User类：

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;
    }
    
}

servlet :

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
    }
}

ajax实现:

<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>

输出：zah 123

访问Map的话直接把返回函数改成如下即可：

success:function(json){ 
    alert(json.u1.username)
}