使用jason需要导入的jar包-java.lang.NoClassDefFoundError

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json-lib-2.3-jdk15.jar

commons-beanutils-1.7.0.jar
commons-httpclient-3.1.jar
commons-lang-2.3.jar
commons-logging-1.0.4.jar
commons-collections-3.1.jar
ezmorph-1.0.3.jar
这些包可以从一下地方下载：
http://commons.apache.org/index.html
http://json-lib.sourceforge.net/
http://ezmorph.sourceforge.net/
http://www.docjar.com/
如果不关联这些包，则会出现以下错误：
java.lang.NoClassDefFoundError: net/sf/ezmorph/Morpher
java.lang.NoClassDefFoundError: org/apache/commons/collections/map/ListOrderedMap
java.lang.NoClassDefFoundError: org/apache/commons/beanutils/DynaBean
java.lang.NoClassDefFoundError: org/apache/commons/codec/DecoderException
java.lang.NoClassDefFoundError: org/apache/commons/lang/exception/NestableRuntimeException
java.lang.NoClassDefFoundError: org/apache/commons/logging/LogFactory

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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;
    }

}
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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
        System.out.print(str);
        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
    }
}
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<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>
  </head>
  <body>
    <input type="button" name="b" value="测试" onclick=test()>
  </body>