Link Details

But what was the reason for the leak??

It's all in the article - it was the implementation of java.util.logger together with a badly named logger..

But why, how, where, ...?
"I tried to look through all the usages of the logger, but it was impossible." - That's no enough.

I also explained that we use the logger tool in many locations, so I couldn't seek the usage of the logger.
I later explain that eventually it was the request for a logger with a name that changes constantly - "apparently a user decided to have the timestamp (System.currentTimeMillis) added to one of the logger name requests." and the conclusion: "It seems that the Java Logger keeps a lot of information as cached".

The leak was not in java.util.logger per-se; it was a misuse of it that caused it.

Note that the use of weak/soft references alluded to in the comments is not actually implemented in the Java runtime today - until Java 7 is released.

Thanks for the info, William. Where can I find more about this, actually?

JDK 7 sources and http://bugs.sun.com/view_bug.do?bug_id=6274920