extjs - 如何在javascript中解析一个json对象

Question

我有两个 JSON 对象，我必须在 ExtJs 网格中显示这是我的网格，我从 Servlet 获得的数据我得到一个空的网格

//getting the response from Servlet

 var proxy=new Ext.data.HttpProxy({url:'LoginServlet'}); // this is the Servlet


var reader=new Ext.data.JsonReader( //store 

 {

 },[
     {name:'username',mapping:'username'}, //field s of Grid
     {name:'password'}//

   var store=new Ext.data.Store({  //data Store 

  proxy:proxy, //proxy
  reader:reader,//
  root:"obj" //
   });

   store.load(); //loding the store


   var grid=new Ext.grid.GridPanel({   //creating the Grid panel

   store:store,//
   columns:[

       {header:"username",width:60,dataIndex:'username'}, //setting 
       {header:"password",width:60,dataIndex:'password'}
   ],
   renderTo:Ext.getBody(),
   width:420, //
   height:200