解决ajax返回验证的时候总是弹出error错误的方法

发一个简单案例：
前台：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
 <head>
   <title>用户登录</title>
   <script type="text/javascript" src="../js/jquery-easyui-1.3.5/jquery.min.js"></script>
   <script type="text/javascript" src="../js/jquery-easyui-1.3.5/jquery.easyui.min.js"></script>
   <link rel="stylesheet" href="../js/jquery-easyui-1.3.5/themes/default/easyui.css" type="text/css"></link>
   <link rel="stylesheet" href="../js/jquery-easyui-1.3.5/themes/icon.css" type="text/css"></link>
   <script type="text/javascript" src="../js/jquery-easyui-1.3.5/locale/easyui-lang-zh_CN.js"></script>
   <meta http-equiv="content-type" content="text/html;charset=UTF-8" />
   <script type = "text/javascript" charset = "UTF-8">
   $(function(){
     var loginDialog;
     loginDialog = $('#loginDialog').dialog({
       closable : false , // 组件添加属性：让关闭按钮消失
       //modal : true, //模式化窗口
       buttons : [{
         text:'注册',
         handler:function(){ 

         }
       },
       {
         text:'登录',
         handler:function(){
            $.ajax({
             url:'../servlet/Login_Do',
             data :{
                name:$('#loginForm input[name=name]').val(),
                password:$('#loginForm input[name=password]').val()
               },
             dataType:'json',
             success:function(r){
              //var dataObj=eval("("+data+")");
               alert("进来了");
             },
             error:function(){
               alert("失败");
             }   

           });
            //alert(data)
         }
       }]
     });
   });
   </script>
 </head>
 <body style=”width:100%;height:100%;" >
    <div id = "loginDialog" title = "用户登录" style = "width:250px;height:250px;" >
      <form id = "loginForm" method = "post">
        <table>
        <tr>
          <th>用户名 :</th>
          <td><input type = "text" class = "easyui-validatebox" data-options="required:true" name = "name"><br></td>
        </tr>
        <tr>
          <th>密码: </th>
          <td> <input type = "password" class = "easyui-validatebox" data-options="required:true" name = "password"><br></td></td>
        </tr>
        </table>
      </form>
    </div>
 </body>
</html> 

后台：

public class Login_Do extends HttpServlet {
  public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
      this.doPost(request, response);
  }
  public void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    request.setCharacterEncoding("UTF-8");
    response.setCharacterEncoding("UTF-8");
    String name =request.getParameter("name");
    String password = request.getParameter("password");
    String js = "{\"name\":name,\"password\":password}";
    PrintWriter out = response.getWriter();
    JSONObject json = new JSONObject();
    json.put("name",name);
    out.print(json.toString());
    response.getWriter().write(json.toString());
  }
}

点击登录时：

解决办法：弹出error信息一般有两种可能：
第一种：url错误，后台直接得不到值
可以用火狐的firebug查看：如果响应了信息，则不是这个问题，那么就有可能是第二种情况：
返回数据类型错误：
在我这个例子中，返回的数据无意中打印了两次,这两句删去一句就好了：

out.print(json.toString());
response.getWriter().write(json.toString());  

造成了错误。这时在firebug显示的信息是：

以上就是为大家分析的用ajax返回验证的时候总是弹出error的原因，希望对大家解决此类问题有所帮助。