Apache Commons seems to be the decent Object Pool implementation out there. Or any other framework that could support the cause
How Can I save its state of the pool during shutdown; may be serialize its objects to a external form json, xml ..? and reload during next startup ?
It is possible to capture objects in a pool when the pool is closed and put these objects back in the pool when a pool is opened with Yapool. I added a test-case to Yapool that shows how this could be done.
Persisting these objects "between pools" is not part of Yapool. But you can, for example, store them in a file and load them before a pool is opened.
Update: added another test-case which shows a more proper implementation and also shows a corner-case.