session mix up

[samar hasan]

i have a web application running on oracle 9i database and tomcat 5 with jdk 1.4. everything was doing fine until the # of users using the application increased (about 300 users) sessions started mixing. so i used single thread model in my servlets . sessions sttopped mixing but the application (at the peak hour) is very slow. could someone please tell me what to do? i want to get rid of the single threadmodel and keep my sessions away from mixing. does changing to another application server help? JBOSS or tomcat 6??? is there is something wrong with my code??? F1 help help

[David Newton]

is there is something wrong with my code???

Most likely.

[samar hasan]

here is a sample of my code

[David Newton]

Please UseCodeTags.

[samar hasan]

import java.io.IOException; 
import java.text.DecimalFormat; 
import java.util.Vector; 

import javax.servlet.*; 


import javax.servlet.*; 


public class QryController extends HttpServlet { 

private HttpServletRequest request = null; 
private HttpServletResponse response = null; 
private HttpSession session = null; 


public void performTask() { 

String from = request.getRequestURI(); 
from = from.substring(from.lastIndexOf("/")); 
try { 
response.setHeader("Cache-Control", "no-cache"); 
response.setHeader("Pragma", "no-cache"); 
response.setDateHeader("Expires", 0); 
response.setHeader("Expires", "0"); 


if (from.endsWith("ListEmpVac")) { 

ListEmpVac(); 
} 
else if (from.endsWith("ListVacDetails")) { 

ListVacDetails(); 
} 


} catch (Exception e) { 
e.printStackTrace(); 
} 

} 

/*******************************************************************************/ 
public void ListEmpVac() { 

ListVacDao VacCredit = new ListVacDao(); 

String empno = (String) session.getAttribute("empno"); 
EmpBean VacList = VacCredit.getVacList(empno); 

request.setAttribute("VacList", VacList); 
try { 
forward("/vacation.jsp"); 
return; 
} catch (Exception e) { 
e.printStackTrace(); 
} finally { 
VacCredit.EndConnection(); 
} 

} 

/*******************************************************************************/ 
public void ListVacDetails() { 
VacDetailsDao VacDetails = new VacDetailsDao(); 

String empno = (String) session.getAttribute("empno"); 
Vector VDetails = VacDetails.getVacDetails(empno); 
session.setAttribute("VDetails", VDetails); 
request.setAttribute("VDetails", null); 

try { 
forward("/vac_detail.jsp"); 
return; 
} catch (Exception e) { 
e.printStackTrace(); 
} finally { 
VacDetails.EndConnection(); 
} 

} 



/*******************************************************************************/ 

public void doGet(HttpServletRequest request, HttpServletResponse response) { 

doPost(request, response); 
} 

public void doPost(HttpServletRequest request, HttpServletResponse response) { 

this.request = request; 
this.response = response; 
session = request.getSession(false); 
performTask(); 
} 

/*******************************************************************************/ 

protected void forward(String url) throws ServletException, IOException, 
Exception { 

RequestDispatcher forJsp = getServletContext() 
.getRequestDispatcher(url); 

if (forJsp != null) { 
forJsp.forward(request, response); 
} else { 
throw new Exception("RequestDispatcher is null"); 
} 
} 

} 
 

[David Newton]

There is only one instance of each servlet instantiated for each servlet in an application: having non-thread local, non-synchronized instance variables is a complete non-starter.

[David Newton]

Do you really not indent your code?

[samar hasan]

I do indent my code!!!

So what's the problem??

[David Newton]

David Newton wrote:There is only one instance of each servlet instantiated for each servlet in an application: having non-thread local, non-synchronized instance variables is a complete non-starter.

The code above is not indented; don't be surprised if I ask if you indent your code.

[samar hasan]

sorry if it sounds stupid. but i didn't understand what does that mean !!

[David Newton]

You're putting the request, response, and session into instance variables. There is only one instance of the servlet. So *every single request* is using the *same* request, response, and session values: overwriting them, reading from them, etc.

See here for more information; this is very basic Java web app stuff. There are a lot of other resources on the web covering this topic, this just happens to be among the first I found on Sun's website.

[samar hasan]

but why did this problem appeared when the number of users increased???

[David Newton]

Because before there were more users you were lucky and/or didn't notice.

[samar hasan]

Thank you David

[Max Rahder]

Samar: As a rule, never code instance fields in servlets. Furthermore, with servlets (and any kind of programming) you should not use an instance field as a way of "passing" data. I.e., don't have routine A place something in an instance field because you're about to call method B, which needs that value. Instead, simply pass the value to B as a parameter. In your code, pass the request object to performTask(). (And it should pass the request to any routines it calls that need it.)