Working with Entity bean using JPA API
In the previous issue of Java Jazz Up you have learnt how a Stateless Bean is developed in EJB 3. Now you will learn how an Entity Bean is developed to interact with the Database using JPA API.

Entity:

An entity defines a table (consisting of rows and columns) in a relational database. An entity refers to a logical collection of data that can be stored or retrieved from that entity. For example, in a banking application, Customer and BankAccount can be treated as entities.
Customer name, customer address etc can be logically grouped together for representing a Customer entity. Similarly account number, total balance etc may be logically grouped under BankAccount entity.

Mapping with EJB3/JPA Annotations:

The EJB 3.0 entity beans are used to model and access relational database tables. It is a completely POJO-based persistence framework with annotations that specify how the object should be stored in the database. The EJB 3.0 container does the mapping from the objects to relational database tables automatically and transparently. Their mappings are defined through JDK 5.0 annotations (an XML descriptor syntax for overriding is defined in the EJB3 specification).

Annotations can be split in two categories, the logical mapping annotations which allows programmer to describe the object model, the class associations, etc. and the physical mapping annotations which describes the physical schema, tables, columns, indexes, etc. The combination of annotations from both categories makes a JPA-based application. Now, the Java developer no longer needs to worry about for the implementation of home interfaces and the details of the database table
schema, database connection management, and
specific database access APIs.