HttpSession in Java : explanation & example

HttpSession in Java (with example)

The HttpSession object is used for session management. A session contains information specific to a particular user across the whole application.
Session in Java Servlet are managed through different ways, such as
Cookies, HttpSession API,
URL rewriting, etc.

 

Here is an example of using HttpSession object.

 

For this example I will
create a Dynamic Web Application using Eclipse. This Web Application will have 2
servlets:

– MyJavaServlet :
will set a parameter on the session level

– MyJavaServlet2 :
will read that parameter (on the session
level)

package servlets;

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;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class MyJavaServlet
 */
@WebServlet("/MyJavaServlet")
public class MyJavaServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

    public MyJavaServlet() {
        super();
        // TODO Auto-generated constructor stub
    }


	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub

		HttpSession session=request.getSession();  
        session.setAttribute("user_name", "Paul");  
        
		PrintWriter myResponse = response.getWriter();
	    String message = "This servlet set a session variable using HttpSession object. ";
			
	
	    myResponse.println( "\n" +"This servlet set a session variable using HttpSession object.\n" +
	         "\n" +
	         "


Tóm Tắt


" + message + "
\n" +
	         "
   
  
Link to MyJavaServlet2 servlet page : "+
	         "  link
"+
	         "");
	    
	    
	}
}

package servlets;

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;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class MyJavaServlet
 */
@WebServlet("/MyJavaServlet2")
public class MyJavaServlet2 extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    public MyJavaServlet2() {
        super();
        // TODO Auto-generated constructor stub
    }

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub

		HttpSession session=request.getSession();  
        String uname = (String) session.getAttribute("user_name");  
        
		PrintWriter myResponse = response.getWriter();
	    String message = "This servlet read a session variable using HttpSession object. ";
			
	
	    myResponse.println( "\n" +"This servlet read a session variable using HttpSession object.\n" +
	         "\n" +
	         "
" + message + "
\n" +
	         "
   
  
 The User Name read from the HttpSession object is "+ uname+ ".
"+
	         "");
	    
	    
	}
}

The following screen is
the result of MyJavaServlet servlet:

 

 

 

The following screen is
the result of MyJavaServlet2 servlet:

 

 

 

NOTE:

1) If you have an architecture with 2
or more web servers in a cluster (not only 1 web container), the values stored in the session object of one server
(container),  might not be available in the session object on the other server
(container). This is because a web container can not see the attributes from
another (remote) container (which run on another JVM instance).

 

2) To
avoid this problem, you have to :

       
– store the session variable into a database

       
– use sticky session : the user requests will be send to the same container
(server) for the same session.

 

Enjoy HttpSession object !