Hibernate Basic
What is Hibernate?
Hibernate is a pure Java object-relational mapping (ORM) and Persistence framework that allows you to map plain old Java objects to relational database tables using (XML) configuration files.
Hibernate solves object-relational impedance mismatchproblems by replacing direct persistence-related database accesses with high-level object handling functions.
Hibernate 3.0, the Open Source persistence technology at the heart of J2EE EJB 3.0 is available for download from Hibernet.org.The Hibernate 3.0 core is 68,549 lines of Java code together with 27,948 lines of unit tests, all freely available under the LGPL, and has been in development for well over a year.
Goal of Hibernate.
Hibernate 3.0 provides three 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.
To provide automated & optimized techniques.
To reduce the time that developers devote to manual coding & make them concentrated more on business logic of their application (25%).
To provide smart fetching & cashing.
To supply a toolset for development.
Automatic Key Generation: Hibernate supports the automatic generation of primary key for your.
Hibernate XML binding enables data to be represented as XML and POJOs interchangeably.
JDBC Vs Hibernate

Relational Persistence for JAVA
Working with both Object-Oriented software and Relational Database is complicated task with JDBC because there is mismatch between how data is represented in objects versus relational database. So with JDBC, developer has to write code to map an object model’s data representation to a relational data model and its corresponding database schema. Hibernate is flexible and powerful ORM solution to map Java classes to database tables. Hibernate itself takes care of this mapping using XML files so developer does not need to write code for this.
Transparent Persistence
The automatic mapping of Java objects with database tables and vice versa is called Transparent Persistence. Hibernate provides transparent persistence and developer does not need to write code explicitly to map database tables tuples to application objects during interaction with RDBMS. With JDBC this conversion is to be taken care of by the developer manually with lines of code.
Support for Query Language
JDBC supports only native Structured Query Language (SQL). Developer has to find out the efficient way to access database, i.e to select effective query from a number of queries to perform same task. Hibernate provides a powerful query language Hibernate Query Language (independent from type of database) that is expressed in a familiar SQL like syntax and includes full support for polymorphic queries. Hibernate also supports native SQL statements. It also selects an effective way to perform a database manipulation task for an application.
Database Dependent Code
Application using JDBC to handle persistent data (database tables) having database specific code in large amount. The code written to map table data to application objects and vice versa is actually to map table fields to object properties. As table changed or database changed then it’s essential to change object structure as well as to change code written to map table-to-object/object-to-table. Hibernate provides this mapping itself. The actual mapping between tables and application objects is done in XML files. If there is change in Database or in any table then the only need to change XML file properties.
Maintenance Cost
With JDBC, it is developer’s responsibility to handle JDBC result set and convert it to Java objects through code to use this persistent data in application. So with JDBC, mapping between Java objects and database tables is done manually. Hibernate reduces lines of code by maintaining object-table mapping itself and returns result to application in form of Java objects. It relieves programmer from manual handling of persistent data, hence reducing the development time and maintenance cost.
Optimize Performance
Caching is retention of data, usually in application to reduce disk access. Hibernate, with Transparent Persistence, cache is set to application work space. Relational tuples are moved to this cache as a result of query. It improves performance if client application reads same data many
times for same write. Automatic Transparent Persistence allows the developer to concentrate more on business logic rather than this application code. With JDBC, caching is maintained by hand-coding.
Disadvantages of Hibernate
Steep learning curve.
Use of Hibernate is an overhead for the applications which are :
- simple and use one database that never change.
- need to put data to database tables, no further SQL queries.
- there are no objects which are mapped to two different tables. Hibernate increases extra layers and complexity. So for these types of applications JDBC is the best choice.
Support for Hibernate on Internet is not sufficient.
Anybody wanting to maintain application using Hibernate will need to know Hibernate.
For complex data, mapping from Object-to-tables and vise versa reduces performance and increases time of conversion.
Hibernate does not allow some type of queries which are supported by JDBC. For example It does not allow to insert multiple objects (persistent data) to same table using single query. Developer has to write separate query to insert each object.