本文主要是向大家介绍如何通过Ajax检测用户名占用与否的相关资料，通过示例代码介绍非常详细，对大家的学习或工作都有一定的参考和学习价值，需要学习的朋友们下面和小编一起学习吧

适用人群： Ajax和 jQuery入门

使用 Ajax进行用户名验证

给 jQuery提供提示信息

当用户注册时，用 Ajax实现检测用户名是否已注册，很多细节没有实现，给大家做一个简单普及。

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<%@ 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("www.51iyq.com");
        $("#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。

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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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