Learning JPA

Have simple aim: get acquainted with JPA through few examples and then check how it can be used in my current project.

Possible usages:

• Use current SAP NetWeaver implementation of JPA for simple ORM usages and create all needed services around it
• Put proprietary mature repository with stable codebase and vast offer of services as a JPA persistence agent and allow developers use it with a simple, but powerfull JPA programming model

So first steps is to find the simplest platform to experiment with. Plain J2SE JPA implementation seems very tempting.