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From "Caldarale, Charles R" <Chuck.Caldar...@unisys.com>
Subject RE: Singletons in Tomcat(6.0)
Date Tue, 01 Dec 2009 14:33:49 GMT
> From: jkv [mailto:j.kumaravel@gmail.com]
> Subject: Singletons in Tomcat(6.0)
> 
> Is using singleton patterns in Tomcat (in servlets programming and
> deploying them in tomcat) a really bad idea??

No, it's fine.

> One really useful post is
> http://wiki.apache.org/tomcat/OutOfMemory

Unfortunately, the section on singletons in that page is completely bogus.  Keeping an instance
of a class in a static variable of that class does not inhibit garbage collection in any way
in a current JVM.  I suspect the author was using a GC method in an older JVM where class
unloading was disabled, or he simply didn't wait long enough for the class to be discarded
(calling System.gc() won't do it).

The comment about starting extra threads is also erroneous.  As long as your webapp manages
the threads by using a ServletContextListener to shut them down when the webapp is stopped,
there's no problem.

 - Chuck


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