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适合人群：Ajax和jQuery入门
采用Ajax实现用户名验证
使用jQuery给出提示信息
用户注册的时候，使用Ajax实现检测用户名是否已经被注册过，很多细节没有实现，给大家做个简单普及。
<%@ page language=”java” contentType=”text/html; charset=utf-8″
pageEncoding=”utf-8″%>
<!DOCTYPE html PUBLIC “-//W3C//DTD HTML 4.01 Transitional//EN” “http://www.w3.org/TR/html4/loose.dtd”>
<html>
<head>
<meta http-equiv=”Content-Type” content=”text/html; charset=utf-8″>
<title>用户注册页面</title>
<script src=”https://libs.baidu.com/jquery/1.8.3/jquery.min.js”></script>
<script type=”text/javascript”>
var xmlHttp;
function createXMLHttpRequest(){
if(window.XMLHttpRequest){
xmlHttp = new XMLHttpRequest();
}else if(window.ActiveXObject){
xmlHttp = new ActiveXObject(“Microsoft.XMLHttp”);
}
}
function validate(account){
createXMLHttpRequest();
xmlHttp.open(“Get”,”ValidateServlet?account=”+account,true);
xmlHttp.onreadystatechange = callback;
xmlHttp.send(null);
}
function callback(){
if(xmlHttp.readyState==4){
if(xmlHttp.status==200){
var text = xmlHttp.responseText;
if(text==”true”){
//document.getElementById(“msg”).innerHTML = “该手机号已经被注册过”;
$(“#msg”).text(“该手机号已经被注册”);
$(“#sub”).attr(“disabled”,”true”);//添加disabled属性，让按钮不可用
}else{
//document.getElementById(“msg”).innerHTML = “”;
$(“#msg”).text(“”);
$(“#sub”).removeAttr(“disabled”);//移除disabled属性，让按钮可用
}
}else{
alert(“请求失败，错误码=”+xmlHttp.status);
}
}
}
function checkInfo(){
var account = $(“#account”).val();
var pwd1 = $(“#pwd1”).val();
var pwd2 = $(“#pwd2”).val();
if(account==””||account==null){
$(“#msg”).text(“账号不能为空”);
$(“#sub”).attr(“disabled”,”true”);
return false;
}
if(pwd1==””||pwd1==null||pwd2==””||pwd2==null||pwd1!=pwd2){
$(“#info”).text(“密码不能为空或者两次密码不一致”);
$(“#sub”).attr(“disabled”,”true”);
return false;
}
$(“#msg”).text(“”);
$(“#info”).text(“”);
$(“#sub”).removeAttr(“disabled”);
}
function submit(){
checkInfo();
$(“#reg”).submit();
}
</script>
</head>
<body>
<form id=”reg” name=”reg” action=”RegisterServlet” method=”post”>
账号：<input type=”text” name=”account” id=”account” onblur=”validate(this.value);”>
<span id=”msg” style=”color:red”>请输入手机号</span><br>
密码：<input type=”password” id=”pwd1″ name=”password1″ onblur=”checkInfo();”><br>
确认密码：<input type=”password” id=”pwd2″ name=”password2″ onblur=”checkInfo();”>
<span id=”info” style=”color:red”></span><br>
<input type=”button” id=”sub” value=”提交” onclick=”submit();”>
</form>
</body>
</html>
下面是ValidateServlet模拟实现，没有做真正的数据库表数据检测，大家自行完成。
package com.ambow.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet(“/ValidateServlet”)
public class ValidateServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
public ValidateServlet() {
super();
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
PrintWriter pw = response.getWriter();
String account = request.getParameter(“account”);
System.out.println(“account”+account);
if(“123”.equals(account)) {
pw.print(“true”);
}else {
pw.print(“false”);
}
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
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来源：脚本之家
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