Hibernate is a high-performance Object/Relational persistence and query service that is open source and free to download under the GNU Lesser General Public License (LGPL). Hibernate handles not just the mapping from Java classes to database tables (and from Java data types to SQL data types), but also data query and retrieval. This article is intended for Java programmers who want to learn about the Hibernate framework and its API. 

  1. What is Hibernate?

Hibernate is a JAVA object-relational mapping (ORM) solution. It is an open source persistent framework created by Gavin King in 2001.. It is a strong Object-Relational Persistence and Query service for any Java application. 

Hibernate converts Java classes to database tables and Java data types to SQL data types, relieving the developer of 95% of conventional data persistence programming duties. 

Hibernate stands between typical Java objects and the database server, handling all aspects of object persistence based on the necessary O/R techniques and patterns.

                                                                                  Hibernate Position

2. Advantages of Hibernate 

  • Hibernate handles the mapping of Java classes to database tables using XML files and without the need for any code. 
  • Simple APIs for saving and retrieving Java objects straight from and from the database are provided. 
  • If the database or any table changes, you merely need to modify the XML file properties. 
  • Provides a mechanism to work around familiar Java Objects while abstracting away unknown SQL kinds. 
  • Hibernate does not require the use of an application server to function. 
  • Manipulates complex database object relationships. 
  • Smart fetching techniques reduce database access. 
  • Allows for basic data querying. 

3. Hibernate Architecture 

Hibernate has a layered architecture which helps the user to operate without 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. 

Hibernate uses various existing Java APIs, like JDBC, Java Transaction API(JTA), and Java Naming and Directory Interface (JNDI). JDBC provides a rudimentary level of abstraction of functionality common to relational databases, allowing almost any database with a JDBC driver to be supported by Hibernate. JNDI and JTA allow Hibernate to be integrated with J2EE application servers.

                                                                                 Hibernate Architecture

  • * Configuration Object 

The Configuration object is the first Hibernate object you create in any Hibernate application. It is 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. 

 

  • * SessionFactory Object 

Configuration object is used to create a SessionFactory object which in turn configures Hibernate for the application using the supplied configuration file and allows for a Session object to be instantiated. The SessionFactory is a thread safe object and used by all the threads of an application. 

The SessionFactory is a heavyweight object; it is usually 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.

 

  • * Session Object 

A Session is used to get a physical connection with a database. The Session object is lightweight and designed to be instantiated each time an interaction is needed with the database. Persistent objects are saved and retrieved through a Session object. 

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. 

 

  • * Transaction Object 

A Transaction represents a unit of work with the database and most of the RDBMS supports transaction functionality. Transactions in Hibernate are handled by an underlying transaction manager and transaction (from JDBC or JTA). 

This is an optional object and Hibernate applications may choose not to use this interface, instead managing transactions in their own application code. 

 

  • * Query Object 

Query 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. 

 

  • * Criteria Object 

Criteria objects are used to create and execute object oriented criteria queries to retrieve objects. 

Here is some information about Hibernate, hope the article will help you understand more about it. 

(Source: Tutorialspoint)

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