The common methods of servlet context, session and request objects and the scope of storing data in servlet.

Tips :context,session,request, As Servlet Important means of value transmission between , The distinction between their scopes , The key and difficult points of our study .

Catalog

One 、Servlet Three data storage objects

  ①ServletContext

  ②HttpSession

  ③HttpServletRequest

Three public methods （API）

Two 、 Scope  

ServletContext：（ From server startup to server shutdown .）

HttpSession： One session , When session End on Destruction （ The default is short session , To persist a session, you need to set the maximum lifetime session.setMaxInactiveInterval( Number of seconds );）. 

HttpServletRequest： One request . 

3、 ... and 、 Use scenarios

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Preface ： In this article, we will start with the basic concepts of the three , Start with the advantages and disadvantages of the three , Then analyze the similarities and differences of their scopes .

One 、Servlet Three data storage objects

  ①ServletContext

        WEB Container at startup , It will WEB The application creates a corresponding ServletContext object , It represents the current web application .ServletConfig Maintained in object ServletContext References to objects , Developers are writing servlet when , Can pass config.getServletContext() Methods to get ServletContext object . 

  ②HttpSession

         Created on the server side , Save on server , Maintain on the server side , Every time you create a new Session, The server will assign a unique ID, And put this ID Save to client Cookie in , The form of preservation is JSESSIONID To save the .

  ③HttpServletRequest

        HttpServletRequest Object represents the client's request , When the client passes HTTP When the protocol accesses the server ,HTTP All the information in the request header is encapsulated in this object , Through the methods provided by this object , You can get all the information requested by the client .

Three public methods （API）

Store the data ：setAttribute（name,value）;

get data ：getAttribute（name）;

Delete data ： removeAttribute（name）;

Two 、 Scope  

ServletContext：（ From server startup to server shutdown .）

Test01 

package com.ape.view;

import java.io.IOException;
import java.io.PrintWriter;

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 org.thymeleaf.context.WebContext;

/**
 * Servlet implementation class Test01
 */
@WebServlet("/Test01")
public class Test01 extends HttpServlet {
	private static final long serialVersionUID = 1L;
    
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// 1.  Deal with the mess 
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		request.setCharacterEncoding("utf-8");
		
		// Access to resources 
		PrintWriter out = response.getWriter();
		ServletContext context = getServletContext();
		//request Domain 
		String name = " Pig eight quit ";
		context.setAttribute("name", name);
		// Print to page 
		out.print(" page 1"+context.getAttribute("name"));
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

Test02

package com.ape.view;

import java.io.IOException;
import java.io.PrintWriter;

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;

/**
 * Servlet implementation class Test02
 */
@WebServlet("/Test02")
public class Test02 extends HttpServlet {
	private static final long serialVersionUID = 1L;
    
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// 1.  Deal with the mess 
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		request.setCharacterEncoding("utf-8");
		
		// Access to resources 
		PrintWriter out = response.getWriter();
		ServletContext context = getServletContext();
		//request Domain 
		// Print to page 
		out.print(" page 2"+context.getAttribute("name"));
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

  Running results ：

At present edge Browsers can request

 

  Another Firefox browser can also request

 

HttpSession： One session , When session End on Destruction （ The default is short session , To persist a session, you need to set the maximum lifetime session.setMaxInactiveInterval( Number of seconds );）. 

Test01 

package com.ape.view;

import java.io.IOException;
import java.io.PrintWriter;

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 javax.servlet.http.HttpSession;

import org.thymeleaf.context.WebContext;

/**
 * Servlet implementation class Test01
 */
@WebServlet("/Test01")
public class Test01 extends HttpServlet {
	private static final long serialVersionUID = 1L;
    
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// 1.  Deal with the mess 
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		request.setCharacterEncoding("utf-8");
		
		// Access to resources 
		PrintWriter out = response.getWriter();
		HttpSession session = request.getSession();
		//request Domain 
		String name = " The sand monk ";
		session.setAttribute("name", name);
		// Print to page 
		out.print(" page 1"+session.getAttribute("name"));
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

Test02

package com.ape.view;

import java.io.IOException;
import java.io.PrintWriter;

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 javax.servlet.http.HttpSession;

/**
 * Servlet implementation class Test02
 */
@WebServlet("/Test02")
public class Test02 extends HttpServlet {
	private static final long serialVersionUID = 1L;
    
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// 1.  Deal with the mess 
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		request.setCharacterEncoding("utf-8");
		
		// Access to resources 
		PrintWriter out = response.getWriter();
		HttpSession session = request.getSession();
		//request Domain 
		// Print to page 
		out.print(" page 2"+session.getAttribute("name"));
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

  Running results ：

At present edge Browsers can request

 

  Another Firefox browser cannot be requested

 

 

HttpServletRequest： One request . 

Test01 

package com.ape.view;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Test01
 */
@WebServlet("/Test01")
public class Test01 extends HttpServlet {
	private static final long serialVersionUID = 1L;
    
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// 1.  Deal with the mess 
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		request.setCharacterEncoding("utf-8");
		
		// Access to resources 
		PrintWriter out = response.getWriter();
		
		//request Domain 
		String name = " The Monkey King ";
		request.setAttribute("name", name);
		// Print to page 
		out.print(" page 1"+request.getAttribute("name"));
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

Test02

package com.ape.view;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Test02
 */
@WebServlet("/Test02")
public class Test02 extends HttpServlet {
	private static final long serialVersionUID = 1L;
    
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// 1.  Deal with the mess 
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		request.setCharacterEncoding("utf-8");
		
		// Access to resources 
		PrintWriter out = response.getWriter();
		
		//request Domain 
		// Print to page 
		out.print(" page 2"+request.getAttribute("name"));
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

  Running results ：

 

After forwarding ： （ The address bar doesn't change , but request The request is complete ）

 

 

3、 ... and 、 Use scenarios

Request Domain ： Related to the current operation , You can forward the value to other pages .

Session Domain ： It's a reply , It can only be used in the current browser , It is applicable to those related to user information , For example, save login information .

application Domain ： Public , Can be called during the entire project run , Store global information , Some important information is not recommended .

Finally, everyone ：

The new week is full of vitality (*^▽^*)！！！