1. ServletContext概述

全局对象，也拥有作用域，对应一个Tomcat中的Web应用
当Web服务器启动时，会为每一个Web应用程序创建一块共享的存储区域（ServletContext）
ServletContext在Web服务器启动时创建，服务器关闭时销毁。

2.获取ServletContext对象

GenericServlet提供了getServletContext()方法。this.getServletContext();
HttpServletRequest提供了getServletContext()方法;
HttpSession提供了getServletContext()方法。

package com.qf.servletProject.servlet.controller;

import com.mysql.cj.Session;

import javax.servlet.ServletContext;
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 javax.servlet.http.HttpSession;
import java.io.IOException;
import java.net.HttpURLConnection;

@WebServlet(name = "ServletContextController",value = "/ctxController")
public class ServletContextController extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 1. 通过this.getServletContext();
        ServletContext servletContext = this.getServletContext();

        // 2.通过request对象获取
        ServletContext servletContext1 = request.getServletContext();

        // 3.通过session对象获取
        HttpSession session = request.getSession();
        ServletContext servletContext2 = session.getServletContext();

        System.out.println(servletContext);
        System.out.println(servletContext1);
        System.out.println(servletContext2);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request,response);
    }
}