案例：如果用户名输入为张三，那么在失去焦点时后面会显示该用户名已被注册，否则显示可以注册！
1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> 2 <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> 3 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 4 <html> 5 <head> 6 <meta http-equiv="pragma" content="no-cache"> 7 <meta http-equiv="cache-control" content="no-cache"> 8 <meta http-equiv="expires" content="0"> 9 <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> 10 <meta http-equiv="description" content="This is my page"> 11 <script type="text/javascript"> 12 function createXMLHttpRequest() { 13 try { 14 return new XMLHttpRequest(); 15 } catch (e) { 16 try { 17 return ActvieXObject("Msxml2.XMLHTTP"); 18 } catch (e) { 19 try { 20 return ActvieXObject("Microsoft.XMLHTTP"); 21 } catch (e) { 22 alert("用的是什么浏览器啊？"); 23 throw e; 24 } 25 } 26 } 27 } 28 window.onload = function() { 29 var btn = document.getElementById("t1"); 30 btn.onblur = function() { 31 var xmlHttp = createXMLHttpRequest(); 32 xmlHttp.open("POST", "<c:url value='/AServlet'/>", true); 33 xmlHttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded"); 34 xmlHttp.send("username="+btn.value); 35 xmlHttp.onreadystatechange = function() { 36 if(xmlHttp.readyState == 4 && xmlHttp.status == 200) { 37 var text = xmlHttp.responseText; 38 var mesg=""; 39 if(text=="1") mesg="<font color='red'>用户名已被注册！</font>"; 40 if(text=="0") mesg="<font color='blue'>用户名可以注册！</font>"; 41 var spn1 = document.getElementById("spn1"); 42 spn1.innerHTML = mesg; 43 } 44 }; 45 }; 46 }; 47 </script> 48 </head> 49 <body> 50 用户名：<input type="text" id="t1"><span id="spn1"></span><br><br> 51 密 码：<input type="password"> 52 <h1 id="h1"></h1> 53 </body> 54 </html>
1 import java.io.IOException; 2 import javax.servlet.ServletException; 3 import javax.servlet.http.HttpServlet; 4 import javax.servlet.http.HttpServletRequest; 5 import javax.servlet.http.HttpServletResponse; 6 public class AServlet extends HttpServlet { 7 public void doPost(HttpServletRequest request, HttpServletResponse response) 8 throws ServletException, IOException { 9 request.setCharacterEncoding("UTF-8"); 10 String username = request.getParameter("username"); 11 if(username.equals("张三")) response.getWriter().print("1"); 12 else response.getWriter().print("0"); 13 } 14 }
运行截图：
