Ajax使用原生态JS实现用户名是否存在验证

直接上代码:
reg_ajax.html


<html>
<head>
<meta charset="UTF-8">
<title>Ajax请求servlet实现用户名是否存在验证title>
head>
<body>

    <script type="text/javascript"> /** * 得到XMLHttpRequest对象 */ function getajaxHttp() { var xmlHttp; try { // Firefox, Opera 8.0+, Safari  xmlHttp = new XMLHttpRequest(); } catch (e) { // Internet Explorer  try { xmlHttp = new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) { try { xmlHttp = new ActiveXObject("Microsoft.XMLHTTP"); } catch (e) { alert("您的浏览器不支持AJAX!"); return false; } } } return xmlHttp; } /** * 发送ajax请求 * url--请求到服务器的URL * methodtype(post/get) * con (true(异步)|false(同步)) * functionName(回调方法名,不需要引号,这里只有成功的时候才调用) * (注意:这方法有二个参数,一个就是xmlhttp,一个就是要处理的对象) */ function ajaxrequest(url, methodtype, con, functionName) { //获取XMLHTTPRequest对象 var xmlhttp = getajaxHttp(); //设置回调函数(响应的时候调用的函数) xmlhttp.onreadystatechange = function() { //这个函数中的代码在什么时候被XMLHTTPRequest对象调用? //当服务器响应时,XMLHTTPRequest对象会自动调用该回调方法 if (xmlhttp.readyState == 4) { if (xmlhttp.status == 200) { functionName(xmlhttp.responseText); } } }; //创建请求 xmlhttp.open(methodtype, url, con); //发送请求 xmlhttp.send(); } function checkUsername() { var username=document.getElementById('username').value; //调用ajax请求Servlet ajaxrequest("userServlet?username="+username,"POST",true,ckUsernameResponse); } function ckUsernameResponse(responseContents){ if (responseContents=='yes') { document.getElementById('usernameMsg').innerHTML="用户名存在"; document.getElementById('username').style="background-color: red"; }else{ document.getElementById('usernameMsg').innerHTML=""; document.getElementById('username').style="background-color: white"; } } script>

    <table>
        <tr>
            <td>用户名td>
            <td><input type="text" id="username" onblur="checkUsername()"/>td>
            <td><div id="usernameMsg">div>td>
        tr>
        <tr>
            <td>邮箱td>
            <td><input type="text" id="email" />td>
            <td><div id="emailMsg">div>td>
        tr>
    table>


body>
html>

请求的Servlet代码如下;
UserServlet.java

package cn.bestchance.servlet;

import java.io.IOException;
import java.util.ArrayList;

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

/** * Servlet implementation class UserServlet */
@WebServlet("/userServlet")
public class UserServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;


    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username=request.getParameter("username");
        //这里使用ArrayList代替从数据库中查询数据
        ArrayList userList =new ArrayList();
        userList.add("admin");
        userList.add("test");
        userList.add("chance");
        //验证用户名是否存在
        boolean flag = false;
        for (String string : userList) {
            if(string.equals(username)){
                flag = true;
                break;
            }
        }
        if(flag){//用户名已存在
            response.getWriter().print("yes");
        }else{//用户名不存在
            response.getWriter().print("no");
        }
    }

}

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