直接上代碼:
reg_ajax.html
<!DOCTYPE html><html><head><meta charset="UTF-8"><title>Ajax請求servlet實現用戶名是否存在驗證</title></head><body> <script type="text/javascript"> /** * 得到XMLHttpRequest對象*/ 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("您的瀏覽器不支持AJAX！"); return false; } } } return xmlHttp; } /** * 發送ajax請求* url--請求到服務器的URL * methodtype(post/get) * con (true(異步)|false(同步)) * functionName(回調方法名，不需要引號,這裡只有成功的時候才調用) * (注意：這方法有二個參數，一個就是xmlhttp,一個就是要處理的對象) */ function ajaxrequest(url, methodtype, con, functionName) { //獲取XMLHTTPRequest對象var xmlhttp = getajaxHttp(); //設置回調函數（響應的時候調用的函數） xmlhttp.onreadystatechange = function() { //這個函數中的代碼在什麼時候被XMLHTTPRequest對象調用？ //當服務器響應時，XMLHTTPRequest對象會自動調用該回調方法if (xmlhttp.readyState == 4) { if (xmlhttp.status == 200) { functionName(xmlhttp.responseText); } } }; //創建請求xmlhttp.open(methodtype, url, con); //發送請求xmlhttp.send(); } function checkUsername() { var username=document.getElementById('username').value; //調用ajax請求Servlet ajaxrequest("userServlet?username="+username,"POST",true,ckUsernameResponse); } function ckUsernameResponse(responseContents){ if (responseContents=='yes') { document.getElementById('usernameMsg').innerHTML="<font color='red'>用戶名存在</font>"; document.getElementById('username').style="background-color: red"; }else{ document.getElementById('usernameMsg').innerHTML=""; document.getElementById('username').style="background-color: white"; } } </script> <table> <tr> <td>用戶名</td> <td><input type="text" id="username" onblur="checkUsername()"/></td> <td><div id="usernameMsg"></div></td> </tr> <tr> <td>郵箱</td> <td><input type="text" id="email" /></td> <td><div id="emailMsg"></div></td> </tr> </table></body></html>請求的Servlet代碼如下，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"); //這裡使用ArrayList代替從數據庫中查詢數據ArrayList<String> userList =new ArrayList<String>(); userList.add("admin"); userList.add("test"); userList.add("chance"); //驗證用戶名是否存在boolean flag = false; for (String string : userList) { if(string.equals(username)){ flag = true; break; } } if(flag){//用戶名已存在response.getWriter().print("yes"); }else{//用戶名不存在response.getWriter().print("no"); } }}以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持武林網。