Vibur DBCP is a mature and complete JDBC connection pool library which has been in active development for 3+ years now, and which offers between others:
non-starvation guarantee for application threads
advanced performance monitoring capabilities
Hibernate 3.6.x, 4.x and 5.x integration support, as separate modules
caching support for JDBC Statements (Prepared and Callable)
Vibur requires Java 1.7.
(if it's trivial it might be quicker to re-emplement it, to avoid any legal paperwork)
My whole project is ASL 2.0 licensed, hope this works well for you? I'm happy to go the donation / legal task path if needed. Note that I have ConnectionProvider implementation for Hibernate 3.6, 4.x, and 5.[0-1], but not for 5.2 - this is the point where a change was introduced in Hibernate. Let me know how you want to continue.
Also, I'm guessing that you're considering the integration for your 5.x branches only, is this correct?
And of course, I'll be able to help with choosing the default configuration values for Vibur where needed, etc.
ASL 2.0 would work but LGPL would be preferred mainly because the rest of the codebase is LGPL.
And yes, the idea would be that the new module would only be moving forward. Technically we could add it to 5.2, but I'd really only "announce it" for whatever comes after 5.2 (whether that be 5.3 or 6.0 is still to be decided in the next few months).
Since the code already exists in Vibur (albeit in form that needs some tweaking for 5.2) as Sanne points out the actual work should be pretty trivial. I really comes down to the legalese as Sanne also mentions.
If I need to sign on any legalese please just contact me by my personal email.