In the Dec 2007 issue of Java Jazz Up magazine, we have discussed a lot of details about the Hibernate. In the current issue we are taking you further in the same direction but this time we are talking about the
annotations with the hibernate.

Hibernate needs a metadata to govern the transformation of data from POJO to database tables and vice versa. Most commonly XML file is used to write the metadata information in Hibernate

Annotations : A Brief Overview

The Java 5 version has introduced a powerful way to provide the metadata to the JVM. The mechanism is known as Annotations. Annotation is the java class which is read through reflection mechanism during the
runtime by JVM and does the processing accordingly. The Hibernate Annotations is the powerful way to provide the metadata for the Object and Relational Table mapping. All the metadata is clubbed into the POJO java file along with the code this helps the user to understand
the table structure and POJO simultaneously during the development. This also reduces the management of different files for the metadata and java code.

Prerequisites for setting up a project :

1. Make sure to have Java 5.0 or a higher version.
2. Hibernate Core 3.2.0GA and above.
3. Download and add the Hibernate- Annotations jar file in the project workspace.
   

Prerequisites for setting up a project :

Let us assume we have a table Employee which has only two columns i.e ID and Name. In hibernate core to achieve the mapping for the above employee table the user should create the following files

1. Utility file for configuring and building the session factory.
2. 2. Hibernate.cfg.xml or any other Datasource metadata file
3. Employee POJO object.
4. Real application file which has the actual logic manipulate the POJO

Note:- Annotations are only the step to remove the hbm.xml file so all the steps remain same only some modifications in some part and adding the annotation data for the POJO.

Please note that coming example will use the Employee table from the database. The SQL query to create the employee table is as follows :-

Create table Employee( ID int2 PRIMARY KEY, NAME n varchar(30) );

Step 1:- Creating A simple Utility Class

The following is the code given for the utility class for sessionFactory

package net.roseindia;
import org.hibernate.SessionFactory;
import
org.hibernate.cfg.AnnotationConfiguration;
public class HibernateUtil {
private static final SessionFactory
sessionFactory;
static {
try {
// Create the SessionFactory from
hibernate.cfg.xml
sessionFactory = new
AnnotationConfiguration().configure().buildSessionFactory();
}
catch (Throwable ex) {
// Make sure you log the exception, as it
might be swallowed
System.err.println(“Initial SessionFactory
creation failed.” + ex);
throw new
ExceptionInInitializerError(ex);
}
}