使用ajax校验用户是否存在

发布时间：2020-12-16 01:29:52 所属栏目：百科来源：网络整理

导读：页面： %@ page language="java" import="java.util.*" pageEncoding="UTF-8"%%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"html head titleMy JSP 'ajax3.jsp' starting

页面：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>My JSP 'ajax3.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">
//创建异步对象
function createXMLHttpRequest() {
	try {
		return new XMLHttpRequest();//大多数浏览器
	} catch (e) {
		try {
			return ActvieXObject("Msxml2.XMLHTTP");//IE6.0
		} catch (e) {
			try {
				return ActvieXObject("Microsoft.XMLHTTP");//IE5.5及更早版本	
			} catch (e) {
				alert("您的浏览器不支持");
				throw e;
			}
		}
	}
}


window.onload = function() {
	// 获取文本框，给它的失去焦点事件注册监听
	var userEle = document.getElementById("usernameEle");
	userEle.onblur = function() {
		//1.得到异步对象
		var xmlHttp = createXMLHttpRequest();
		//2.打开连接
		//xmlHttp.open("POST","<c:url value='/ValidateUsernameServlet'/>",true);
		xmlHttp.open("POST","/Web/ValidateUsernameServlet",true);
		//3.设置请求头：Content-Type
		xmlHttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
		//4.发送请求，给出请求体
		xmlHttp.send("username=" + userEle.value);
		
		//5.给xmlHttp的onreadystatechange事件注册监听
		xmlHttp.onreadystatechange = function() {
			if(xmlHttp.readyState == 4 && xmlHttp.status == 200) {//双重判断
				//获取服务器的响应，判断是否为1
				// 是：获取span，添加内容：“用户名已被注册”
				var text = xmlHttp.responseText;
				var span = document.getElementById("errorSpan");
				if(text == "1") {
					//得到span元素
					span.innerHTML = "用户名已被注册！";
				} else {
					span.innerHTML = "";
				}
			}
		};
	};
};
</script>
  </head>
  
  <body>
<h1>演示用户名是否被注册</h1>
<form action="" method="post">
用户名：<input type="text" name="username" id="usernameEle"/><span id="errorSpan"></span><br/>
密　码：<input type="password" name="password"/><br/>
<input type="submit" value="注册"/>
</form>
  </body>
</html>

ValidateUsernameServlet

package com.java.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ValidateUsernameServlet extends HttpServlet {

	protected void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException {
		request.setCharacterEncoding("utf-8");
		response.setContentType("text/html; charset=utf-8");
	
		String username = request.getParameter("username");
		if(username.equals("itachi")) {
			response.getWriter().print("1");
		} else {
			response.getWriter().print("0");
		}
	}

}

（编辑：李大同）

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