var ajax = Ext.Ajax.request({
      url: "test.action",
      params: {
      },
      success: function(response, option) {
      },
      failure: function(response, option) {
      }
});

------解决方案--------------------
将你后台得到的数据通过
getResponse().setContentType("text/javascript;charset=UTF-8");
PrintWriter out = getResponse().getWriter();
out.write(content);
就ok了
然后直接return  null；

------解决方案--------------------

Java code

 function checkLgoin()
     {  
           if (userForm.getForm().isValid()) {
                      userForm.getForm().submit({
                  //   formBind: true,     
                    // waitMsg:"正在验证，请等待。。",
                    method:"POST",
                     url:"user/userLog!checkUserModify.action",
              success:function (form,action)
              {
                   Ext.Msg.alert('提示信息',action.result.Info);
                 
                   userForm.hide();
                  window.parent.rightFrame.location="testExtjs/eMain.jsp"
              },
              failure : function(form, action) {
                    Ext.MessageBox.alert("提示信息",action.result.Info);
                }
               });
       }
     }