A singleton lifespan in Tomcat

[Alexandre Brizard]

Hi!

I have a singleton class that operates on a Tomcat server. When I
start Tomcat, everything is fine, I have only one instance of the
class. But, if I modify the web.xml file, per example, and the context
is stopped then restarted, the instance I had in the first place isn't
destroyed and continues to run, and another singleton is created when I
call the getInstance() method of the singleton. How do I fix that?

Here are some excerpts of my class:

public class ConnectionPool {

private static ConnectionPool instance = null;
..
..
..
public synchronized static ConnectionPool getInstance()
throws SQLException, ClassNotFoundException {
if (instance == null){
instance = new
ConnectionPool(m_driverName,m_dbURL,m_user,m_password);
}
return instance;
}
..
..
..
};

Thanks!

 

[Chris Smith]

I have a singleton class that operates on a Tomcat server. When I
start Tomcat, everything is fine, I have only one instance of the
class. But, if I modify the web.xml file, per example, and the context
is stopped then restarted, the instance I had in the first place isn't
destroyed and continues to run, and another singleton is created when I
call the getInstance() method of the singleton. How do I fix that?

Both of the basic singleton implementations in Java rely on the
uniqueness of static variables. When you load a new web application in
Tomcat (including if you modify a file that convinces Tomcat to reload
your web app for you), Tomcat will create a new servlet context class
loader, and the new class loader will load new classes that have their
own static variables.

Since the new web application will not have access to the old instance,
you need to swap over to the new instance. That probably means properly
closing your old instance when you're finished with it. Try adding a
listener to the servlet context to do that.

Google turns this up:

http://www.stardeveloper.com/articles/display.html?article=2001111901&page=1

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