Oh my God, I don't understand why I cannot use static maps to store user information.

Sorry folks, it was a long time since the last post, but I promisse that I am going back to stay.

Today we will take about a issue that I have heard about in the office for the whole last week: memory leak.

I believe that some memory leak is ok to happen, mainly if you store things on the HttpSession. Let's be realistics, it is a easy solution and if the data keeps on the memory for 30 minutes who cares?

But actually the memory leak that we have found is not realted to the session, it was related to the 2 different issues: thread variables and static maps.

• Thread variables: a lot of things were being stored into the thread variable, and using as key some object. First, usually the web servers reuse the threads, so the information there was being keep for a looong time. Second object as key SHOULD-ALWAYS-NO EXCUSE TO NOT HAVE hash, otherwise baby, guess what? Every add is a new entry on the map. That's a bingo: memory leak.
• Static maps: this is just a more obvious leak than the thread variables, use a static map to store information, where the key also do not implement a proper comparation methods. So every entry lead to a forever-and-ever information into the memory. As as Murphy says: there is always something worst, those information stored into the map where GUI objects, which was reference even to God. And the leak could lead to a OutOfMemory after 5 screen hits.

Nice ins't it? I can understand the problems, what I cannot understand is people blaming the GUI obejcts to have the necessary references. Come on, they are GUI objects that are supposed to work for a single request.
But the real problem is that people still tries to solve problems that are not present yet. The performance problems are the classical example: you never run the application, so you don't know if there is performance problems or not. Why should you address them? Why to worry about it?
Most of the problems could be solve with a proper approach to the problem and not with cache (that usually leads to a whole bunch of other problems). And if the cache is need think about what are you doing: my key if unique? is it replacing the information? what is the live time of the data? should I need another cache than the HttpSession? ...

Make like the buddhists: breath 10 times before doing something, if after that time you still want to do it, go and think about it and then do it, otherwise just go home and relax.