function sub(){
    
     if(document.forms[0].username.value==''){
         alert('请填写登录名！');   
         document.forms[0].username.focus();
     }else{
         if(document.forms[0].password.value==''){
             alert("请填写密码！");
             document.forms[0].password.focus(); 
         }else{
             checkLoginUser(document.forms[0].username.value,document.forms[0].password.value);
             //form1.submit();
         }
     }
 }
 
 function checkLoginUser(username,password){ 
      Ext.Ajax.request({
            url : 'checkLogin.action',
            params :{password:password,username:username},
            method: 'post',
            success: function(result, request ){
                var resp =new Ext.util.JSON.decode(result.responseText);   
                if(resp.success=="true"){
                    if(resp.isallow=="allow"){
                       openIndex();
                    }else if(resp.isallow=="reject"){
                         openRegPage(resp.orgtype);
                    }else{
                    }
                   }else{
                       alert('登陆失败,用户名或密码错误。');   
                   }
            },
            failure: function(result, request){
                  alert('登陆失败,请稍候再试。');   
            }
          });
       }

------解决方案--------------------
写到登陆页面中登陆按钮的js里就可以了