08ServletContext

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);
    }
}

08ServletContext

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);
    }
}

08ServletContext


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);
    }
}

08ServletContext

 

 

 


 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);
    }
}

08ServletContext

 

     

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