I am specifically looking for JPA code generation technique
First, what are all the project could generate JPA compliant code? (Eg. HibernateTools)
Second, I
The ideal tool/eclipse plugin for jpa code reverse generation is Hibernate Tools. This has now been made a part of JBoss Tools. So, in your eclipse start off with installing JBoss Tools.
Then create a JPA Project. This project will act as the holder of all your code/configurations related to the reverse generation project. Installing the JBoss Tools first gives you the advantage that your Hibernate Configuration(part of Hibernate Tools) gets created along with your JPA project.
Next step would be to use the Hibernate Tools to actually reverse generate your JPA POJO entities corresponding to your database tables.
To understand the steps for JPA POJO reverse generation in detail you can have a look at the following tutorial...http://www.javabrahman.com/j2ee/how-to-do-reverse-code-generation-of-hibernatejpa-pojo-entities-using-jboss-tools-eclipse-plugin/
The above tutorial also has links to tutorials for creating a JPA Project and also for installing JBoss Tools in your eclipse installation both of which are pre-requisites for JPA POJO entities reverse code generation.