Hibernate is a well known object-relational mapping library (ORM) for Java. It allows you to map entries in your relational database to objects in your Java classes.
Usually this is done by a mapping file written in XML. As this approach is a bit more expensive we will use annotations to map a class to the relating database table.
Based on the Maven tutorial by my colleague Phillip, we will begin with a quickstart archetype and include Hibernate and a MySQL connection. Then we will write a simple data access object (DAO) which maps to the database table we will create. After that we use a class to set up the connection and fill the database with some of our objects.
Note: This is just a superficial glance at Hibernate to get in touch with the framework.
Setting up the project
After generating the quickstart archetype we will extend the pom.xml. Add the following dependencies:
<!-- hibernate with annotations for persistence -->
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-entitymanager</artifactId>
<version>3.3.2.GA</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-annotations</artifactId>
<version>3.3.1.GA</version>
</dependency>
<!-- connector to mysql -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.6</version>
</dependency>
The first two extensions add hibernate support and annotation support. The third one provides the the connection to MySQL.
The Database Parts
Now we will create a simple database table to store our data and add a corresponding class. Let’s pretend we want to store interesting coordinates. We just use a description, the longitude and latitude. Additionally we use an id as our primary key which will autoincrement.
CREATE TABLE `hibernateexample`.`coordinatestorage` ( `id` INT NOT NULL AUTO_INCREMENT, `description` VARCHAR(100) NOT NULL, `longitude` FLOAT NOT NULL, `latitude` FLOAT NOT NULL, PRIMARY KEY (`id`) )
The Java class looks according, using annotations for the mapping.
package com.unitedcoders.dao;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name = "coordinatestorage")
public class CoordinateStorage {
@Id
@GeneratedValue
Integer id;
@Column
String description;
@Column
Float longitude;
@Column
Float latitude;
// ... following Getter and Setter, cut out for brevity
That’s about all we need to store the data but we’re still lacking the connection to the database. Create a hibernate.properties file in you classpath and fill it with the appropriate values.
hibernate.dialect=org.hibernate.dialect.MySQLDialect hibernate.connection.driver_class=com.mysql.jdbc.Driver hibernate.connection.url=jdbc:mysql://localhost/hibernateexample hibernate.connection.username=root hibernate.connection.password=root
The Application
To test the persistence classes we will set up a simple Java class, get a session, create some objects and save them into the database.
package com.unitedcoders;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.classic.Session;
import com.unitedcoders.dao.CoordinateStorage;
public class FillDatabase {
public static void main(String[] args) {
AnnotationConfiguration configuration = new AnnotationConfiguration();
configuration.addAnnotatedClass(CoordinateStorage.class);
SessionFactory sessionFactory = configuration.buildSessionFactory();
Session session = sessionFactory.openSession();
for (Float i = 0.0F; i < 10.0F; i++) {
CoordinateStorage coStorage = new CoordinateStorage();
coStorage.setDescription("Location " + i);
coStorage.setLatitude((i * i * 12) % 360);
coStorage.setLongitude((i * i * 55) % 360);
session.save(coStorage);
}
session.close();
sessionFactory.close();
}
}
Final Words
As you can see it's fairly simple to get Hibernate integration in your project. We just looked a very minimal feature set here and integrated Hibernate manually. For a real application you would configure the project differently.
For more information refer to the Hibernate documentation and especially to the available annotations.
Nico Heid
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