ajax實(shí)現(xiàn)簡(jiǎn)單實(shí)時(shí)驗(yàn)證功能

%@ page contentType="text/html;charset=UTF-8" language="java" isELIgnored="false" %>
html>
head>
  title>login/title>
/head>
body>

    用戶名：input type="text" name="username" id="username" onchange="CallServer()"/>
    !-- 顯示提示信息 -->
    div id="msg">/div>
    !-- 在jsp頁(yè)面中引入js，絕對(duì)路徑的方式 -->
    script src="${pageContext.request.contextPath}/js/main.js">/script>
/body>
/html>

alert("use ajax!")
//創(chuàng)建XMLHttpRequest對(duì)象，在不同瀏覽器
function createXMLHTTP() {
  if(window.XMLHttpRequest){
    // IE7+, Firefox, Chrome, Opera, Safari 瀏覽器執(zhí)行代碼
    xmlhttp = new XMLHttpRequest();
  }else {
    // IE6, IE5 瀏覽器執(zhí)行代碼
    xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
  }
  return xmlhttp;
}
function CallServer() {
  var username = document.getElementById("username").value;
  // 判斷為空
  if ((username == null) || (username == "")) return;
  var xmlhttp = createXMLHTTP();
  // 構(gòu)建請(qǐng)求url
  var url = "/loginServlet"+"?"+"username="+username;
  //狀態(tài)碼改變調(diào)用事件
  xmlhttp.onreadystatechange = function () {
    //正常返回，替換msg內(nèi)容
    if(xmlhttp.readyState == 4  xmlhttp.status == 200){
      document.getElementById("msg").innerHTML = xmlhttp.responseText;
    }
  }
  //異步提交請(qǐng)求
  xmlhttp.open("GET",url,true);
  //發(fā)送請(qǐng)求
  xmlhttp.send();
}

!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >
web-app>
 display-name>Archetype Created Web Application/display-name>
 welcome-file-list>
  welcome-file>index.jsp/welcome-file>
 /welcome-file-list>
 servlet>
  servlet-name>loginServlet/servlet-name>
  servlet-class>com.lbw.servlet.loginServlet/servlet-class>
 /servlet>
 servlet-mapping>
  servlet-name>loginServlet/servlet-name>
  url-pattern>/loginServlet/url-pattern>
 /servlet-mapping>
/web-app>

package com.lbw.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;
import java.io.PrintWriter;
/**
 * 后端使用Servlet處理請(qǐng)求
 */
public class loginServlet extends HttpServlet {
  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //設(shè)置編碼和響應(yīng)頭
    request.setCharacterEncoding("UTF-8");
    response.setContentType("text/xml;charset=UTF-8");
    response.setHeader("Cache-Control", "no-cache");
    //獲取參數(shù)
    String username = request.getParameter("username");
    String msg = "";
    if("lbw".equals(username)){
      msg = "名稱正確";
    }else {
      msg = "名稱錯(cuò)誤";
    }
    PrintWriter out = response.getWriter();
    out.println(msg);
  }
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doPost(request,response);
  }
}