Java Persistence with Hibernate

5.3. Creating custom mapping types

Object-oriented languages like Java make it easy to define new types by writing new classes. This is a fundamental part of the definition of object-orientation. If we were then limited to the predefined built-in Hibernate mapping types when declaring properties of our persistent classes, we would lose much of Java's expressiveness. Furthermore, our domain model implementation would be tightly coupled to the physical data model, because new type conversions would be impossible.

Most ORM solutions that we have seen provide support for user-defined strategies for performing type conversions. These are often called converters. For example, the user can create a new strategy for persisting a property of JDK type ...