I have a thread cleaner in my code that is being created if the DB capacity was exceeded, the capacity is checked on every insertion to the DB. I would like to add more functionality to this cleaner and clean also when number of files exceeding, lets say 10000 files. The new functionality should run scheduled.
I want to be able to clean the DB in 2 ways:
1. On demand.
2. Scheduled, every day on X hour.
Which concurrent java class to use?
How can I make sure that the same thread will be used by the 2 ways above?
Code that would perform cleanup of DB should be completely separated out of scheduling (single responsibility principle), so that you could execute it at any time from some other code.
As for scheduling, I would suggest you looking at Quartz scheduler, and get familiar with CRON so that you could extract it to properties to have possibility to change scheduling trigger without modifying your code.
You should synchronize your code so that no more than one cleanup gets performed at the same time, this should be easy with standard synchronize.
If you wish to make it very simple and don't want to add new dependencies, you can go with standard Java solution: Timer. Timer#scheduleAtFixedRate can provide fixed rate execution. Which means you'll have to add extra code whenever new requirements will show up (e.g., don't schedule at weekend).