1.什么是AJAX?
AJAX 是与服务器交换数据并更新部分网页的艺术，在不重新加载整个页面的情况下.
2.简单的AJAX操作
这是项目的目录
a.第一步:写MyJsp.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> <% String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <base href="<%=basePath%>"> <title>My JSP ‘MyJsp.jsp‘ starting page</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page"> <!-- <link rel="stylesheet" type="text/css" href="styles.css"> --> <script> var xmlHttpReq; //创建一个XmlHttpRequest对象 function createXmlHttpRequest() { if(window.XMLHttpRequest) { xmlHttpReq = new XMLHttpRequest();//非IE浏览器 }else { xmlHttpReq = new ActiveXObject("Microsoft.XMLHTTP");//IE浏览器 } } //检测用户名是否已经被注册 function checkUser() { var username = document.getElementById("user").value; if(username=="") { alert("用户名必须填写！"); return false; } //首先XmlHttpRequest创建对象 createXmlHttpRequest(); //指明准备状态改变时回调的函数名 xmlHttpReq.onreadystatechange=handle; //尝试以异步的get方式访问某个URL //请求服务器端的一个servlet var url = "a?username="+username; xmlHttpReq.open("get",url,true); //向服务器发送请求 xmlHttpReq.send(null); } //状态发生改变时回调的函数 function handle() { //准备状态为4 if(xmlHttpReq.readyState==4) { //响应状态码为200，代表一切正常 if(xmlHttpReq.status==200) { //来自服务器的响应,得到服务器上的msg var res = xmlHttpReq.responseText; var result = document.getElementById("result"); result.innerHTML = "<font color=red>"+res+"</font>"; } } } </script> </head> <body> <center><h1>表单注册(AJAX,入门)</h1></center> <p>通过客户端脚本，判断您已经输入了用户名，然后去创建一个组件（XMLHTTP），异步地将用户名提交到服务器检测，服务器会把检测结果输出给客户端组件，那么客户端组件在知道结果后，就可以通过DOM去显示结果。我们不明白这个不要紧，先来看ajax应用的第一个demo（这里做了一个前台HTML页面和一个后台Servlet）:</p> <hr> 姓名: <input type="text" id="user"> <input type="button" value="检测用户名" onclick="checkUser()"> <span id="result"></span> </body> </html>
b:第二部:a.java
package servlet; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class a extends HttpServlet { /** * Constructor of the object. */ public a() { super(); } /** * Destruction of the servlet. <br> */ public void destroy() { super.destroy(); // Just puts "destroy" string in log // Put your code here } /** * The doGet method of the servlet. <br> * * This method is called when a form has its tag value method equals to get. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html,utf-8"); String user = request.getParameter("username"); System.out.println(user); String msg = null; if("zou".equals(user)) { msg = "can not use,beacause it has been there."; }else { msg = "can use"; } response.getWriter().println(msg); } /** * The doPost method of the servlet. <br> * * This method is called when a form has its tag value method equals to post. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); out.print("得到表单的数据为: "+request.getParameter("k")); System.out.println(request.getParameter("k")); } /** * Initialization of the servlet. <br> * * @throws ServletException if an error occurs */ public void init() throws ServletException { // Put your code here } }
运行结果:
以上是第一次接触做的Demo,以后碰到继续
