The Hibernate architecture is layered to keep you isolated from having to know the underlying APIs. Hibernate makes use of the database and configuration data to provide persistence services (and persistent objects) to the application.
There are 4 layers in hibernate architecture java application layer, hibernate framework layer, backhand api layer and database layer. Let's see the diagram of hibernate architecture:
Following is a detailed view of the Hibernate Application Architecture with few important core classes.
Hibernate framework uses many objects session factory, session, transaction etc. alongwith existing Java API such as JDBC (Java Database Connectivity), JTA (Java Transaction API) and JNDI (Java Naming Directory Interface).
Elements of Hibernate ArchitectureFor creating the first hibernate application, we must know the elements of Hibernate architecture. They are as follows:
ConfigurationThe Configuration object is the first Hibernate object you create in any Hibernate application and usually created only once during application initialization. It represents a configuration or properties file required by the Hibernate. The Configuration object provides two keys components:
- Database Connection: This is handled through one or more configuration files supported by Hibernate. These files are hibernate.properties and hibernate.cfg.xml.
- Class Mapping Setup: This component creates the connection between the Java classes and database tables..
SessionFactoryThe SessionFactory is a factory of session and client of ConnectionProvider. It holds second level cache (optional) of data. The org.hibernate.SessionFactory interface provides factory method to get the object of Session.
The SessionFactory is heavyweight object so usually it is created during application start up and kept for later use. You would need one SessionFactory object per database using a separate configuration file. So if you are using multiple databases then you would have to create multiple SessionFactory objects.
SessionThe session object provides an interface between the application and data stored in the database. It is a short-lived object and wraps the JDBC connection. It is factory of Transaction, Query and Criteria. It holds a first-level cache (mandatory) of data. The org.hibernate.Session interface provides methods to insert, update and delete the object. It also provides factory methods for Transaction, Query and Criteria.
The session objects should not be kept open for a long time because they are not usually thread safe and they should be created and destroyed them as needed.
TransactionThe transaction object specifies the atomic unit of work. It is optional. The org.hibernate.Transaction interface provides methods for transaction management.
This is an optional object and Hibernate applications may choose not to use this interface, instead managing transactions in their own application code.
ConnectionProviderIt is a factory of JDBC connections. It abstracts the application from DriverManager or DataSource.
Hibernate Connection management service provide efficient management of the database connections. Database connection is the most expensive part of interacting with the database as it requires a lot of resources of open and close the database connection.
TransactionFactoryIt is a factory of Transaction.
QueryQuery objects use SQL or Hibernate Query Language (HQL) string to retrieve data from the database and create objects. A Query instance is used to bind query parameters, limit the number of results returned by the query, and finally to execute the query.
CriteriaCriteria object are used to create and execute object oriented criteria queries to retrieve objects.
Hibernate provides a lot of flexibility in use. It is called "Lite" architecture when we only uses the object relational mapping component. While in "Full Cream" architecture all the three component Object Relational mapping, Connection Management and Transaction Management) are used.
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