刚刚接触Ext，我用了Ext中的grid　这个东西　．我只是想实现　把database中的信息查出来，显示在grid中．查询的过程放到一个servlet中了．但是怎么不执行这个servlet呢　．　不知道那的问题．十分感谢．

js:如下
<link rel="stylesheet" type="text/css" href="extjs/resources/css/ext-all.css" />
<script type="text/javascript" src="extjs/adapter/ext/ext-base.js"></script>
<script type="text/javascript" src="extjs/ext-all.js"></script>
<script type="text/javascript">
Ext.onReady(function(){
var clickfunction = function(){
var ds = new Ext.data.Store({
  proxy: new Ext.data.HttpProxy({url:'/LookServlet'}),
  reader: new Ext.data.JsonReader({
  totalProperty:'totalProperty',
  root:'root'},
  [
  {name:'company'},
  {name:'price'},
  {name:'change'},
  {name:'change_'},
  {name:'lastupdated'}
  ])
  });
 
  var cm = new Ext.grid.ColumnModel([
    {header:"company", dataIndex:"company",sortable:true},
    {header:"price" ,dataIndex:"price",sortable:true},
    {header:"change",dataIndex:"change",renderer:function change(val){
if(val > 0){
return '<span style="color:green;">' + val + '</span>';
}else if(val < 0){
return '<span style="color:red;">' + val + '</span>';
}
return val;
} ,sortable:true},
    {header:"change_" ,dataIndex:"change_" ,renderer:function pctChange(val){
if(val > 0){
return '<span style="color:green;">' + val + '%</span>';
}else if(val < 0){
return '<span style="color:red;">' + val + '%</span>';
}
return val;
},sortable:true},
    {header:"lastupdated" ,dataIndex:"lastupdated",sortable:true}
  ]);

  var grid = new Ext.grid.GridPanel({
  ds:ds,
  cm:cm
  });
  ds.load();
}
Ext.get('aa').on('click',clickfunction);
});
</script>

在servlet中你转化为json格式的数据没有，另外有没有把json格式数据读到输出流中。就是response.getWriter().write(json);

最好是在firebug里看看 到底报什么错误