使用Ajax实现用户名验证-优快云博客

本文介绍了一种使用Ajax技术实现实时用户名验证的方法。通过在客户端编写JavaScript代码，结合服务器端的Servlet处理程序，可以有效地在用户输入用户名时即时反馈是否已被占用。此方案适用于需要进行快速响应的应用场景。

Ajax 代码模板：

清单一：index.jsp 代码

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8" contentType="text/html; charset=UTF-8"%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    
    <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">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->
	
	<script type="text/javascript">
		var xmlHttp;
		function verify(){		
   			var username=document.getElementById("username").value;
			try	{
   				
    			xmlHttp=new XMLHttpRequest(); // Firefox, Opera 8.0+, Safari
    		} catch (e){
  				
   				try{
   				    xmlHttp=new ActiveXObject("Msxml2.XMLHTTP"); // Internet Explorer
      			} catch (e){
      			
      				try{
         				xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
         			}catch (e){
         				alert("您的浏览器不支持AJAX！");
         				return false;
         			}
         			
      			}
    		}

			//注册回调函数
			xmlHttp.onreadystatechange=callback;
			//设置连接信息
			var url = encodeURI(encodeURI("check?username="+username)); //页面端两次encodeURI
			//xmlhttp.setRequestHeader( "Content-Type", "text/html;charset=UTF-8" );//设置编码
			xmlHttp.open("GET",url,true);
			//发送数据，开始与服务器端交互
			xmlHttp.send(null);	 
		}
		
		//回调函数代码如下：
		function callback(){
			//判断交互是否完成
			if(xmlHttp.readyState==4){
			//判断http的交互是否成功
				if(xmlHttp.status==200){
					//获取服务器端的纯文本数据
					var responseText=xmlHttp.responseText;
					document.getElementById("show").innerHTML=responseText;			
				}else{
					alert("出错了");
				}
			}
		}
	</script>
  </head>
  
  <body>
	<form action="" >
	 用户名：	<input type="text" name="username" onBlur="verify();" id="username"><div id="show"></div><br>
	 密码：	<input type="text" name="password"><br>
	 <input type="submit">
	</form>

  </body>
</html>

清单二：Servlet代码

package com.asm.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.net.URLDecoder;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class AjaxServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		this.doPost(req, resp);
	}

	@Override
	protected void doPost(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		request.setCharacterEncoding("UTF-8");
		response.setContentType("text/html;charset=UTF-8");
		String username = URLDecoder.decode(request.getParameter("username"),
				"UTF-8");
		PrintWriter out = response.getWriter();
		out.write("你输入的用户名为：<font color='red'>" + username+"</font>");
	}
}

ajax :get