15 AJAX - 15.2 AJAX 快速入门 - 《JavaWeb 教程》

AJAX的html文件
后端 Servlet代码

AJAX的html文件

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    // 1. 创建核心对象
    var xhttp;
    if (window.XMLHttpRequest) {
        xhttp = new XMLHttpRequest();
    } else {
        // code for IE6, IE5
        xhttp = new ActiveXObject("Microsoft.XMLHTTP");
    }
    // 2. 发送请求
    <!-- 要写前后端都要访问，写绝对路径 -->
    xhttp.open("GET", "http://localhost:8080/ajax-demo/ajaxServlet");
    xhttp.send();
    // 3. 获取响应
    xhttp.onreadystatechange = function() {
        if (this.readyState == 4 && this.status == 200) {
            alert(this.responseText);
        }
    };
</script>
</body>
</html>

后端 Servlet代码

package com.itheima.web.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;
@WebServlet("/ajaxServlet")
public class AjaxServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 1. 响应数据
        response.getWriter().write("hello ajax");
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request,response);
    }
}