Hibernate is an open-source, high-performance Object Relational Mapping (ORM) tool. It is a lightweight query service that performs the mapping between Java classes and database tables and also offers data retrieval facilities. Persistent data is a prevalent aspect of applications and Hibernate is the best solution to deal with it.
Hibernate forms a layer between the application and the database and loads configuration details such as entity classes, connection strings, mappings etc. The efficient ORM tool creates persistent objects that help synchronize the data between the database and the applications.
Hibernate creates an object of the entity class. The object, called transient object, is neither associated with a session nor is it persisted to the database. An object is created of the SessionFactory Interface and it implements the pattern of the Factory design. Hibernate.cfg.xml file is loaded by the SessionFactory interface. The interface then implements the configuration settings of the database with help from ConnectionProvider and TransactionFactory. The ORM tool has transaction APIs built into it that abstract the application away from the JTA or JDBC transaction that lies underneath.
The hibernate framework brings along a number of advantages.
Lightweight and Open-source: Hibernate is a concise query service that is free for download to all under the Lesser General Public License (LGPL).
High Performance: The hibernate framework provides fast services as it uses the cache internally. It has two types of cache- first and second level cache.
Automated Table Creation: With the hibernate framework, developers need not create database tables manually. They get created automatically.
Database Independent Query: Hibernate Query Language or HQL is a version of that is object-oriented. Hibernate generates queries that works across different databases and thus database-specific queries are not required.
Simplicity: Hibernate can simplify complex join operations so that data can easily fetched from more than one table of the database.
Updates: Hibernate Query Language offers query statistics and the status of the database.
Before downloading and installing hibernate, you must have the latest edition of Java already installed on the system. Depending on whether you will install HQL on Unix or Windows, download the .tz file for installation on Unix and the .zip file in Windows. You can download its latest version latest version here.
Once hibernate has been downloaded, unzip the Installation file and you will find a directory structure. You have to set the CLASSPATH variable accurately in order to ensure errorless compilation. So, copy the library files into the CLASSPATH and modify the variable so that it can include every JAR. Now, copy the primary JAR file, hibernate3.jar, into the CLASSPATH.
There are many APIs in the Hibernate framework and thus it takes some time and effort to get the hang of this query language. As HQL generates a number of SQL statements during runtime, it tends to be slower than JDBC. But it is still the best possible way to tackle persistent data, a thing that is present across applications. So, the time and effort that goes into learning Hibernate.
Read here Hibernate Interview Questions and Answer