ServletContext概述

概念:代表整个web应用可以和程序的容器（服务器）来通信

获取：

通过request对象获取
- request.getServletContext();
通过HttpServlet获取
- this.getServletContext();

java代码

package com.bai.ServletContext;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
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("/ServletContextDemo01")
public class ServletContextDemo01  extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1.通过request对象获取
        ServletContext context1 = req.getServletContext();
        //2.通过HttpServlet获取
        ServletContext context2 = this.getServletContext();

        System.out.println(context1);
        System.out.println(context2);

        System.out.println(context1 == context2);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

运行结果

功能：

获取MiME类型
- MIME类型:在互联网通信过程中定义的一种文件数据类型
  - 格式：大类型/小类型 text/html image/jeag

- 获取:String getMimeType(String file)

java代码

package com.bai.ServletContext;

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 java.io.IOException;

@WebServlet("/ServletContextDemo02")
public class ServletContextDemo02 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //1.通过HttpServlet获取
        ServletContext context2 = this.getServletContext();
        //2.定义文件名称
        String filename="a.jpg";
        //3.获取MINE类型
        String mimeType = context2.getMimeType(filename);
        System.out.println(mimeType);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

运行结果

域对象:共享数据
1. setAttribute(String name,Object value) 保存数据
2. getAttribute(String name) 获取数据
3. removerAttribute(String name)
- ServletContext对象范围：所有用户所有请求的数据

java代码

ServletContextDemo03

package com.bai.ServletContext;

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 java.io.IOException;

@WebServlet("/ServletContextDemo03")
public class ServletContextDemo03 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //1.通过HttpServlet获取
        ServletContext context2 = this.getServletContext();
        //保存数据
        context2.setAttribute("msg","hello");
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

ServletContextDemo04

package com.bai.ServletContext;

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 java.io.IOException;

@WebServlet("/ServletContextDemo04")
public class ServletContextDemo04 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //1.通过HttpServlet获取
        ServletContext context2 = this.getServletContext();
        //获取数据
        Object msg = context2.getAttribute("msg");
        System.out.println(msg);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

运行结果

获取文件的真实（服务器）路径

1. 方法：String getRealpath(String path)

在web文件夹下创建a.txt文件

获取web文件下的服务器路径 java代码

package com.bai.ServletContext;

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 java.io.IOException;

@WebServlet("/ServletContextDemo05")
public class ServletContextDemo05 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //通过HttpServlet获取
        ServletContext context = this.getServletContext();
        //获取web文件下的服务器路径
        String path = context.getRealPath("/a.txt");
        System.out.println(path);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

运行结果

获取web下WEB-INF文件下的服务器路径 java代码

package com.bai.ServletContext;

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 java.io.IOException;

@WebServlet("/ServletContextDemo05")
public class ServletContextDemo05 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //通过HttpServlet获取
        ServletContext context = this.getServletContext();
        //获取web下WEB-INF文件下的服务器路径
        String path = context.getRealPath("/WEB-INF/a.txt");
        System.out.println(path);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}