本質：ServletContext是servlet的中介軟體，為servlet儲存一些東西

　　注：ServletContext是鄰駕與servlet之上的

1.ServletContext概述：

　　web容器在啟動時，它會為每一個web程式都建立一個ServletContext物件，它代表當前的web應用

1.1共享資料

　　在此Servlet中儲存資料，可在另一個servlet中拿到；

package com.king.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
 
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws
 
 ServletException, IOException {

        //this.getInitParameter(); servlet引數
        //this.getServletConfig(); servlet配置
        //this.getServletContext(); servlet上下文
        ServletContext context = this.getServletContext();

        String username="king";//資料
        context.setAttribute("username",username);//
 
將一個數據儲存在ServletContext中，名字為：username

    }

}

package com.king.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String username = (String) context.getAttribute("username");

        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        resp.getWriter().print("名字"+username);

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

web.xml配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                      http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

    <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.king.servlet.HelloServlet</servlet-class>
    </servlet>
    <!--Servlet的請求路徑-->
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/king</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>getc</servlet-name>
        <servlet-class>com.king.servlet.GetServlet</servlet-class>
    </servlet>
    <!--Servlet的請求路徑-->
    <servlet-mapping>
        <servlet-name>getc</servlet-name>
        <url-pattern>/getc</url-pattern>
    </servlet-mapping>

</web-app>