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
AJAX了解内容
原文地址：https://www.cnblogs.com/zoulingjin/p/8467724.html