Hibernate

Hibernate is an Open Source persistence technology. Hibernate maps the Java classes to the database tables. It also provides the data query and retrieval facilities that significantly reduces the development time. It is most useful with object-oriented domain modes and business logic in the Java-based middle-tier. Hibernate allows transparent persistence that enables the applications to switch any database. Hibernate can be used in Java Swing applications, Java Servlet-based applications, or J2EE applications using EJB session beans.

Features of Hibernate

•     Hibernate provides full-featured query facilities: Hibernate Query Language, the newly enhanced Hibernate Criteria Query API, and enhanced support for queries expressed in the native SQL dialect of the database.

•     Filters for working with temporal (historical), regional or permissioned data.

•     Enhanced Criteria query API: with full support for projection/aggregation and subselects.

•     Runtime performance monitoring: via JMX or local Java API, including a second-level cache browser.

•     Hibernate is Scalable: Hibernate has high performance and due to its dual-layer architecture can be used in the clustered environments.

•     Less Development Time: Hibernate reduces the development timings as it supports inheritance, polymorphism, composition and the Java Collection framework.

•     Automatic Key Generation: Hibernate supports the automatic generation of primary key for your.

      In Hibernate, Java classes represent the table in the database and then map the instance variable in the class with the columns in the stabase. Then Hibernate can perform the operations like select, insert, update and delete by automatically creating the quiries.

Hibernate architecture has three main components:

1. Connection Management: provides efficient management of the database connections. 
2. Transaction management: provides the ability to the user to execute more than one database statements at a time.
3. Object relational mapping: technique of mapping the data representation from an object model to a relational data model and is used to select, insert, update and delete the records form the underlying table. When we pass an object to a Session.save() method, Hibernate reads the state of the variables of that object and executes the necessary query.

Hibernate uses the hibernate.cfg.xml to create the connection pool and setup required environment. Plain Old Java Objects (POJOs) classes are used to map to the database table and configure the variables to map to the database column.A xml file is used to map  Object to the  table in the database. Hibernate Session is the main runtime interface between a Java application and Hibernate. SessionFactory allows application to create the Hibernate Session by reading the configuration from hibernate.cfg.xml file.  Then the save method on session object is used to save the contact information to the database: