package com.itheima.web.servlet;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet("/selectUserServlet")
public class SelectUserServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1. 接收用户名
String username = request.getParameter("username");
//2. 调用service查询User对象
//模拟成true
boolean flag = true;
//3. 响应标记
response.getWriter().write(""+flag);
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doGet(request, response);
}
}
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>欢迎注册</title>
<link href="css/register.css" rel="stylesheet">
</head>
<body>
<div class="form-div">
<div class="reg-content">
<h1>欢迎注册</h1>
<span>已有帐号？</span> <a href="login.html">登录</a>
</div>
<form id="reg-form" action="#" method="get">
<table>
<tr>
<td>用户名</td>
<td class="inputs">
<input name="username" type="text" id="username">
<br>
<span id="username_err" class="err_msg" style="display: none">用户名已存在</span>
</td>
</tr>
<tr>
<td>密码</td>
<td class="inputs">
<input name="password" type="password" id="password">
<br>
<span id="password_err" class="err_msg" style="display: none">密码格式有误</span>
</td>
</tr>
<tr>
<td>验证码</td>
<td class="inputs">
<input name="checkCode" type="text" id="checkCode">
<img src="imgs/a.jpg">
<a href="#" id="changeImg">看不清？</a>
</td>
</tr>
</table>
<div class="buttons">
<input value="注 册" type="submit" id="reg_btn">
</div>
<br class="clear">
</form>
</div>
<script>
//1.给用户名输入框绑定 失去焦点事件onblur
document.getElementById("username").onblur = function () {
//2. 发送AJAX请求
//获取用户名的值
var username = this.value;
//2.1. 创建核心对象
var xhttp;
if (window.XMLHttpRequest){
xhttp = new XMLHttpRequest();
}else {
//code for IE6 IE5
xhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
//2.2. 发送请求
xhttp.open("GET","http://localhost:8080/ajax-demo/selectUserServlet?username="+username);
xhttp.send();
//2.3. 获取响应
xhttp.onreadystatechange = function () {
if (xhttp.readyState == 4 && xhttp.status == 200){
// alert(xhttp.responseText);
//判断
if (this.responseText == "true"){
//用户存在，显示提示信息
document.getElementById("username_err").style.display = '';//设置id为username_err的style的display属性为空字符串
}else {
//用户不存在，清除提示信息
document.getElementById("username_err").style.display = 'none';//设置id为username_err的style的display属性为none
}
}
}
}
</script>
</body>
</html>
标签：username,用户名,验证,xhttp,用户,案例,import,servlet,javax From： https://www.cnblogs.com/Karl-hut/p/17523035.html