jQuery 驗證表單用戶名是否已經被註冊

時間 2019-11-18

原文原文鏈接

jQuery ajax異步請求最經常使用的就是當用戶註冊時，判斷用戶名是否已經被註冊過了。這裏給出完整的代碼。javascript

ajax_form.jspcss

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>表單自動校驗</title>
    
    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">    
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
    <!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->
    <!-- 引入jquery -->
    <script type="text/javascript" src="${pageContext.request.contextPath }/js/jquery-1.9.1.js"></script>
    <script type="text/javascript">
        var flag = 0;
        function lost(){
         $("#sp").html("");
        var datas = $("#form").serialize();//序列化表單的值，把輸入的內容用&符號鏈接起來name=xxx&paw=xxx，用於ajax向後臺發送數據
           //這個元素是jquery對象，須要轉爲dom對象，使用數組下標的方法.也可使用 alert($("#name").val());
           $.ajax({ 
                url: "FromServlet", 
                type:"post",
                data:datas,
                dataType:"html",
                beforeSend: function(){
                 $("#sp").html("");
                },
                success: function(data, textStatus){
                    $("#f").html("");
                    //after的用法：將元素插到指定元素的後面，記住不是包含在裏面。這裏就是<td></td><span></span>的意思
                    $("#tt").after("<span id='f'><font fontsize='5' color='red'>"+data+"</font></span>");
    
                },
                error:function(XMLHttpRequest, textStatus, errorThrown){
                   alert(textStatus);
                }
           });
           
        }
        //表單提交前驗證是否合法
        function form_serialize(){

if($("#sp").text()!=""){
alert("請從新選擇用戶名");
return false;
}
return true;html

        }
        
    </script>

  </head>
  
  <body>
    <form action="FromServlet" onSubmit="return form_serialize()" id="form">
         <table>
            <tr>
            <td>用戶名：</td>
            <td id="tt"><input type="text" name="name" onkeyup="lost()" id="name"/>
            </td>
            <tr>
            <td>密&nbsp;碼</td>
            <td><input type="password" name="password"/></td>
            </tr>
            <tr>
            <td><input type="submit" value="提交" /></td>
            <td><input type="reset" value="重置"/></td>
            </tr>
         </table>
    </form>
  </body>
</html>

服務端代碼：java

FromServlet.javajquery

public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html");
        response.setCharacterEncoding("utf-8");
        String name = request.getParameter("name");
        System.out.println("你輸入的是="+name);
        PrintWriter out = response.getWriter();
        //根據用戶名判斷該用戶名是否已經被註冊了，若被註冊過，則給出提示信息
        UserDao userDao = new UserDao();
        User user = userDao.getUserByName(name);
        if(user!=null){
            out.println("用戶名已經被註冊！");
        }
}