Most popular JPA implementation
eclipselink, hibernate, jpa, persistence, toplink
Solution
That depends. Both solutions work but each has made their own design decisions and depending on you, those might work in your favor or against it.
So I suggest to implement a simple but complete prototype using both technologies (spend a week with each) to learn which one suits you better. Complete means: Implement each use case that you know you'll need, especially a complicated one.
As a guideline, I've found that Hibernate has more features but Eclipse Link gives you better error messages -> I spent less time fixing problems with Link.
On the other hand, Hibernate has more features built in, so I spent less time there to turn requirements into code - when I could find the feature, understand how it works and I didn't run into some odd error message that just left me stumped and running in circles for a couple of days.
Eclipse Link was once a commercial product, so the documentation is better.
Problem
I am a junior programmer and was asked to develop an application that should utilize the Java Persistence API (JPA). Which is the most popular JPA implementation (Hibernate, Toplink, EclipseLink) Can I use any of the above with Apache Tomcat or every implementation is tied to a specific server application ? Are there any good introductory books or tutorials for this subject ?