1. 概念

代表整个web应用，可以和程序的容器(服务器)来通信

2. 获取

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

package cn.itcast.web.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("/servletContextDemo1")

public class ServletContextDemo1 extends HttpServlet {

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

        /*

            ServletContext对象获取：

                1. 通过request对象获取

                    request.getServletContext();

                2. 通过HttpServlet获取

                    this.getServletContext();

         */

        //1. 通过request对象获取

        ServletContext context1 = request.getServletContext();

        //2. 通过HttpServlet获取

        ServletContext context2 = this.getServletContext();

        System.out.println(context1);

        System.out.println(context2);

        System.out.println(context1 == context2);//true

    }

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

        this.doPost(request,response);

    }

}

3. 功能

1. 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/jpeg

　　获取：String getMimeType(String file)

package cn.itcast.web.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("/servletContextDemo2")

public class ServletContextDemo2 extends HttpServlet {

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

        /*

            ServletContext功能：

               1. 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/jpeg

                * 获取：String getMimeType(String file)

                2. 域对象：共享数据

                3. 获取文件的真实(服务器)路径

         */

        //2. 通过HttpServlet获取

        ServletContext context = this.getServletContext();

        //3. 定义文件名称

        String filename = "a.jpg";//image/jpeg

        //4.获取MIME类型

        String mimeType = context.getMimeType(filename);

        System.out.println(mimeType);

    }

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

        this.doPost(request,response);

    }

}

2. 域对象：共享数据
　　1. setAttribute(String name,Object value)
　　2. getAttribute(String name)
　　3. removeAttribute(String name)

　　ServletContext对象范围：所有用户所有请求的数据

package cn.itcast.web.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("/servletContextDemo3")

public class ServletContextDemo3 extends HttpServlet {

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

        /*

            ServletContext功能：

               1. 获取MIME类型：

                2. 域对象：共享数据

                3. 获取文件的真实(服务器)路径

         */

        //2. 通过HttpServlet获取

        ServletContext context = this.getServletContext();

        //设置数据

        context.setAttribute("msg","haha");

    }

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

        this.doPost(request,response);

    }

}
package cn.itcast.web.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("/servletContextDemo4")

public class ServletContextDemo4 extends HttpServlet {

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

        /*

            ServletContext功能：

               1. 获取MIME类型：

                2. 域对象：共享数据

                3. 获取文件的真实(服务器)路径

         */

        //2. 通过HttpServlet获取

        ServletContext context = this.getServletContext();

        //获取数据

        Object msg = context.getAttribute("msg");

        System.out.println(msg);

    }

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

        this.doPost(request,response);

    }

}

3. 获取文件的真实(服务器)路径
            方法：String getRealPath(String path)

package cn.itcast.web.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.File;

import java.io.IOException;

@WebServlet("/servletContextDemo5")

public class ServletContextDemo5 extends HttpServlet {

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

        /*

            ServletContext功能：

               1. 获取MIME类型：

                2. 域对象：共享数据

                3. 获取文件的真实(服务器)路径

         */

        // 通过HttpServlet获取

        ServletContext context = this.getServletContext();

        // 获取文件的服务器路径

        String b = context.getRealPath("/b.txt");//web目录下资源访问

        System.out.println(b);

       // File file = new File(realPath);

        String c = context.getRealPath("/WEB-INF/c.txt");//WEB-INF目录下的资源访问

        System.out.println(c);

        String a = context.getRealPath("/WEB-INF/classes/a.txt");//src目录下的资源访问

        System.out.println(a);

    }

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

        this.doPost(request,response);

    }

}

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