ajax验证用户名是否已存在
ajax验证用户名是否已存在 ，一般选用的是同步请求，因为验证用户是否存在的同时，
一般还要验证用户名是否为空等表单验证。
jsp页面以及ajax验证如下：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%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>My JSP 'index.jsp' starting page</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"><script type="text/javascript" src="js/jquery-1.8.3.js"></script><script type="text/javascript">$(function(){$("#uname").blur(function(){var uname = $(this).val();if(uname==""){$("#remind").html("用户名不能为空");}else{// $.ajax方法实现$.ajax({url:"IsUserServlet",type:"get",data:"uname="+uname,dataType:"text",async:false,success:function(result){$("#remind").html(result);}});// $.get()方法实现，$.post方法也是一样的，post方法不能在地址后面直接传值//$.get("IsUserServlet","uname=" + uname, function(result){//$("#remind").html(result);//},"text");// load()方式实现//$("#remind").load("IsUserServlet","uname=" + uname);}});});</script></head><body>用户名：<input type="text" name="uanme" id="uname" /><span id="remind"></span></body></html>
控制层的servlet代码如下：
public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {User user = new User();// 接收前端输入的用户名String uname = request.getParameter("uname");request.setCharacterEncoding("utf-8");response.setCharacterEncoding("utf-8");UserService userService = new UserServiceImpl();if(userService.login(uname)){response.getWriter().write("用户名已存在");}else{response.getWriter().write("用户名不存在");}}
ajax验证用户名结果示例：
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