08ServletContext

1. Concept

Representative of the web application, the container may program (server) to communicate

2. Obtain

1. Get request object
　　request.getServletContext ();
2. obtained by the HttpServlet
　　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) throwsServletException, IOException {
         / * 

            the ServletContext object acquisition: 
                1. Get request object 
                    request.getServletContext (); 
                2. obtained by the HttpServlet 
                    this.getServletContext (); 
         * / 
        
        // 1. Get request object 
        the ServletContext context1 = request.getServletContext ( );
         // 2 obtained by the HttpServlet 
        the ServletContext = context2 the this .getServletContext (); 

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

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


    }

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

3. Function

1. Get MIME types:
　　MIME Type: Internet communication process defined in the file of one type of data
　　format: Type large / small type text / html image / jpeg

　　obtain: 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) throwsServletException, IOException {
         / * 

            the ServletContext functions: 
               1. Obtain the MIME types: 
                * MIME types: A document type definition of the Internet data communication process 
                    * Format: Type large / small type text / Image HTML / JPEG 

                * Get: String getMimeType (String file) 
                2. domain objects: data sharing 
                real 3. get the file (server) path 
         * / 
        
        // 2. get through HttpServlet 
        the ServletContext context = the this .getServletContext (); 

        // 3. Definition file name 
        String filename = " a.jpg "; // Image / JPEG 


        // 4. Get MIME type 
        String mimeType = context.getMimeType (filename); 
        System.out.println (mimeType);


    }

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

Shared data: 2. domain object
　　1. the setAttribute (String name, Object value)
　　2. the getAttribute (String name)
　　3. removeAttribute (String name)

　　the ServletContext object range: all requested data for all users

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) throwsServletException, IOException {
         / * 

            the ServletContext functions: 
               1. Get MIME type: 

                2. domain objects: shared data 
                3 acquired real (server) path to the file 
         * / 
        
        // 2. HttpServlet obtaining 
        the ServletContext context = the this .getServletContext (); 

        // setting data 
        context.setAttribute ( "MSG", "haha" ); 


    } 

    protected  void the doGet (the HttpServletRequest Request, the HttpServletResponse Response) throws ServletException, IOException {
         the 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) throwsServletException, IOException {
         / * 

            the ServletContext functions: 
               1. Get MIME type: 

                2. domain objects: shared data 
                3 acquired real (server) path to the file 
         * / 
        
        // 2. HttpServlet obtaining 
        the ServletContext context = the this .getServletContext (); 

        // Get data 
        Object MSG = context.getAttribute ( "MSG" ); 
        System.out.println (MSG); 

    } 

    protected  void the doGet (the HttpServletRequest Request, the HttpServletResponse Response) throws ServletException, IOException {
         the this .doPost (Request, Response); 
    } 
}

 

 

 

 3. Get real files (server) path
            method: 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 voidthe doPost (the HttpServletRequest Request, the HttpServletResponse Response) throws ServletException, IOException {
         / * 

            the ServletContext functions: 
               1. Get MIME type: 

                2. domain objects: shared data 
                3 acquired real (server) path to the file 
         * / 
        
        // acquired by the HttpServlet 
        the ServletContext context = the this .getServletContext (); 


        // get the file server path 
        String b = context.getRealPath ( "/ b.txt"); // web directory resource access 
        System.out.println (b);
        // file file = File new new (realpath); 

        String C = context.getRealPath ( "/ the WEB-INF / C.txt"); //Resources under WEB-INF directory access 
        System.out.println (c); 

        String A = context.getRealPath ( "/ WEB-INF / classes / a.txt"); // resources under the src directory access 
        System.out. the println (A); 


    } 

    protected  void the doGet (the HttpServletRequest Request, the HttpServletResponse Response) throws ServletException, IOException {
         the this .doPost (Request, Response); 
    } 
}