Could not open Hibernate Session for transaction

This problem happens when the connection to the database is disconnected or was not created at all by the application, but pool assumes connection is established.
Remedy for this could be checking credential to the database [username, password, host, port] and also checking the connection object before proceeding to database tasks like reading or updating.

Adding session bean to to requested bean using annotation JSF

An association from the table refers to an unmapped class Hibernate Exception

Adding Unicode character to mysql from Java-hibernate

Invocation of init method failed – hibernate exception of caching