Potential memory leak in java.util.logging.Level

Roman Kennke roman.kennke at jpmchase.com
Wed Dec 22 14:36:06 UTC 2010


I believe java.util.logging.Level is potentially memory leaking. This can happen if an application defines its own subclass of Level and is loaded by its own classloader. Level's constructor adds a reference to the new instance of the subclass to its 'known' ArrayList (which is a static field). This instance is never removed from that list. And since this instance holds a reference to its classloader, this means that no classes loaded by that classloader can be unloaded. It could be argued that you should not do crazy stuff with classloaders, but this happens invariably when you deal with applets. I guess similar problems can arise on app servers as well.

I wonder why Level's constructors need to be protected though. If they were public, and new Levels could be created simply by instantiating one, this whole problem would not exist. Then the Level.known list would only reference instances of its own class, which would be problematic, unless you create LOTS of levels, which is unlikely. I don't like static collection fields anyway... too prone to leaking.

Is this a known problem? Is there a solution to this, except not creating custom log levels? How else could custom log levels be created under those circumstances that would not trigger this problem?

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