- The Java Persistence API (JPA) provides an object/relational mapping facility to Java developers for managing relational data in Java applications.
- JPA is a replacement for the much criticized EJB 2.0 and EJB 2.1
- JPA is part of EJB 3.0 specification
- One of the great benefits of JPA is that it is an independent API and can nicely integrate with J2EE as well as J2SE applications
- Supports both annotations and xml based configuration
- JPA is a specification and needs an ORM implementation to work and persist the Java Objects.
- List of ORM frameworks are:
- Hibernate
- Toplink from oracle
- iBatis
- Open JPA
- Future versions of JPA will be defined in a separate JSR/specification rather than in the EJB JSR/specification.
JPA Architecture
- JPA is a lightweight, POJO-based Java framework to persist the Java Objects to the relational database.
- JPA uses metadata (via annotations, via XML or both) to map the persistence objects with the database table
- JPA supports SQL like query language which can be used to execute both static and dynamic queries.
- Using JPA it's also very easy to switch to different ORM frameworks.
- JPA architecture includes the following three components:
- Entity
- EntityManager
- EntityManagerFactory
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| JPA Architecture |
Entity
- An Entity is a class which should be persisted in a database, In other words it Signify that a class is persistent
- Instance of entity represent one record in a table
- All entity classes must define a primary key and must have a default constructor
- By default, the table name corresponds (same) to the class name
- Syntax:
EntityManager
- The EntityManager interface is providing the API for interacting with the Entity, e.g. finds objects, persists them and remove objects from the database, etc.
- In other words it provides the operations from and to the database.
EntityManagerFactory
- The EntityManagerFactory is used to create an instance of EntityManager.
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