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How to solve the problem that error always pops up when ajax returns verification

亚连Original: 2018-05-24 11:29:282562browse

This article mainly introduces the method to solve the problem that error always pops up when ajax returns verification. Interested friends can refer to it

Send a simple case:
Front desk:

<%@ 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 = $(&#39;#loginDialog&#39;).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:&#39;注册&#39;, 
         handler:function(){ 
            
         } 
       }, 
       { 
         text:&#39;登录&#39;, 
         handler:function(){ 
            $.ajax({ 
             url:&#39;../servlet/Login_Do&#39;, 
             data :{ 
                name:$(&#39;#loginForm input[name=name]&#39;).val(), 
                password:$(&#39;#loginForm input[name=password]&#39;).val() 
               }, 
             dataType:&#39;json&#39;, 
             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%;" > 
    <p 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>  
    </p> 
 </body> 
</html>

Backend:

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()); 
  } 
}

When you click to log in:

Solution: There are generally two possibilities for pop-up error messages :
The first type: url error, the value cannot be obtained directly in the background
You can use Firefox's firebug to check: If the message is responded to, this is not the problem, then it may be Second case:
Return data type error:
In my example, the returned data was accidentally printed twice. Just delete one of these two sentences:

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

caused an error. The information displayed in firebug at this time is:

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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