Hibernate - How to maintain a single Session instance Per Thread?

Hibernate is an Object Relation mapping framework for Java language. It has more benefits over JDBC. Since I am using it since 2010, I have found that one of the biggest benefits of Hibernate is that code written using Hibernate is almost database independent and can be a key feature if one wants to shift the code base from one database to another.

Using Hibernate, one has to be careful with the following two

a) A singleton SessionFactory instance should be maintained throughout the application (if using a single database) 

It can be easily done using either a static code block OR implementing the Singleton pattern.

b) Single Session instance should be maintained per Thread

This is a tricky part but luckily we have the ThreadLocal to our rescue. This class provides thread-local variables. Below is the code to maintain a single Session instance per Thread

private static final ThreadLocal<Session> session = new ThreadLocal<Session>();

   public static Session getCurrentSession() {

        Session s  = (Session) session.get();        

        // Open a new Session, if this Thread has none yet

          if  ( (s==null) || (!s.isOpen()) ) {

               s = sessionFactory.openSession();

                session.set(s);

          }

          return s;

    }

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