How do I retrieve a list of Hibernate’s persistent objects?

In this example we add the function to read a list of records in our LabelManager class. This function will read all Label persistent object from database. You can see the other functions such as saveLabel, getLabel and deleteLabel in the related example section of this example.

package org.kodejava.example.hibernate.app;

import org.hibernate.Query;
import org.hibernate.Session;
import org.kodejava.example.hibernate.model.Label;

import java.util.List;

public class LabelManager {

    public List getLabels() {
        Session session = SessionFactoryHelper.getSessionFactory().getCurrentSession();
        session.beginTransaction();

        //
        // We read labels record from database using a simple Hibernate query,
        // the Hibernate Query Language (HQL).
        //
        List labels = session.createQuery("from Label").list();
        session.getTransaction().commit();

        return labels;
    }
    
    public void saveLabel(Label label) {
        //
        // To save an object we first get a session by calling getCurrentSession()
        // method from the SessionFactoryHelper class. Next we create a new
        // transaction, save the Label object and commit it to database,
        //
        Session session = SessionFactoryHelper.getSessionFactory().getCurrentSession();

        session.beginTransaction();
        session.save(label);
        session.getTransaction().commit();
    }    
}
package org.kodejava.example.hibernate.app;

import org.kodejava.example.hibernate.model.Label;

import java.util.Date;
import java.util.List;

public class ListDemo {
    public static void main(String[] args) {
        LabelManager manager = new LabelManager();

        //
        // Creates a Label object we are going to stored in the database. We
        // set the name, modified by and modified date information.
        //
        Label label = new Label();
        label.setName("Sony Music");
        label.setCreated(new Date());

        //
        // Call the LabelManager saveLabel method.
        //
        manager.saveLabel(label);

        List labels = manager.getLabels();
        for (int i = 0; i < labels.size(); i++) {
            label = (Label) labels.get(i);
            System.out.println("Label = " + label);
        }
    }
}

How do I delete persistent object in Hibernate?

Continuing the previous example How do I get object from database in Hibernate?, we now add the delete function in our LabelManager class.

package org.kodejava.example.hibernate.app;

import org.hibernate.Query;
import org.hibernate.Session;
import org.kodejava.example.hibernate.model.Label;

import java.util.List;

public class LabelManager {
    public void deleteLabel(Integer id) {
        //
        // Load the object to be deleted
        //
        Label label = getLabel(id);

        //
        // We get the current session and delete the Label object from database.
        //
        Session session = SessionFactoryHelper.getSessionFactory().getCurrentSession();
        session.beginTransaction();
        session.delete(label);
        session.getTransaction().commit();
    }
}
package org.kodejava.example.hibernate.app;

import org.kodejava.example.hibernate.model.Label;

import java.util.Date;

public class DeleteDemo {
    public static void main(String[] args) {
        LabelManager manager = new LabelManager();

        //
        // Creates a Label object we are going to stored in the database. We
        // set the name and created date information.
        //
        Label label = new Label();
        label.setName("Sony Music");
        label.setCreated(new Date());

        //
        // Call the LabelManager saveLabel method.
        //
        manager.saveLabel(label);

        //
        // Read the object back from database.
        //
        label = manager.getLabel(label.getId());
        System.out.println("Label = " + label);

        manager.deleteLabel(label.getId());
    }
}

How do I retrieve object from database in Hibernate?

In the How do I store object in Hibernate? example you’ll see how tho store objects into database. In this example we’ll extends the LabelManager class and add the capability to get or query object from database.

package org.kodejava.example.hibernate.app;

import org.hibernate.Query;
import org.hibernate.Session;
import org.kodejava.example.hibernate.model.Label;

import java.util.List;

public class LabelManager {
    public Label getLabel(Integer id) {
        Session session = SessionFactoryHelper.getSessionFactory().getCurrentSession();

        session.beginTransaction();

        //
        // We get back Label object from database by calling the Session object
        // get() method and passing the object type and the object id to be
        // read.
        //
        Label label = (Label) session.get(Label.class, id);
        session.getTransaction().commit();

        return label;
    }

    public void saveLabel(Label label) {
        //
        // To save an object we first get a session by calling getCurrentSession()
        // method from the SessionFactoryHelper class. Next we create a new
        // transaction, save the Label object and commit it to database,
        //
        Session session = SessionFactoryHelper.getSessionFactory().getCurrentSession();

        session.beginTransaction();
        session.save(label);
        session.getTransaction().commit();
    }
}
package org.kodejava.example.hibernate.app;

import org.kodejava.example.hibernate.model.Label;

import java.util.Date;

public class SaveLoadDemo {
public static void main(String[] args) {
LabelManager manager = new LabelManager();

//
// Creates a Label object we are going to stored in the database. We
// set the name and created date information.

How do I store object in Hibernate?

This example shows you how to store or save Hibernate object to database. The basic steps in creating application in Hibernate will be:

  • Creates the Pojo
  • Create the Hibernate mapping file
  • Register the mapping file in the Hibernate configuration
  • Create a simple manager class to store the object

In this example we’ll create a class called Label, this class is about a record label company. This class has the id, name, created and modified attributes. Their types in order are Integer, String, java.util.Date and java.util.Date.

Hibernate is an Object Relation Mapping technology which basically means how an object is mapped to a relational database model. Because of this it needs a mapping file to map the object properties to table columns. The mapping file usually named in the format of Label.hbm.xml, the class name with hbm.xml suffix. And for Hibernate application recognize the object, the mapping file should be registered in the Hibernate configuration hibernate.cfg.xml file.

We have a brief introduction about the Hibernate class and configuration structure. Let’s jump the the working example. First we creates the mapping file and then we create the classes.

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="org.kodejava.example.hibernate.model.Label" table="LABELS">
        <id name="id" column="id">
            <generator class="native"/>
        </id>
        <property name="name" not-null="true"/>
        <property name="created" column="created" type="timestamp"/>
        <property name="modified" column="modified" type="timestamp"/>
    </class>
</hibernate-mapping>
package org.kodejava.example.hibernate.model;

import java.util.Date;

public class Label {
    private Integer id;
    private String name;
    private Date created;
    private Date modified;

    // Getters and Setters

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder("[");
        sb.append("id = ").append(id).append("; ");
        sb.append("name = ").append(name).append("]");
        return sb.toString();
    }
}
package org.kodejava.example.hibernate.app;

import org.hibernate.Session;
import org.kodejava.example.hibernate.model.Label;

public class LabelManager {
    public void saveLabel(Label label) {
        // To save an object we first get a session by calling 
        // getCurrentSession() method from the SessionFactoryHelper class. 
        // Next we create a new transaction, save the Label object and 
        // commit it to database,
        Session session = SessionFactoryHelper.getSessionFactory()
                .getCurrentSession();

        session.beginTransaction();
        session.save(label);
        session.getTransaction().commit();
    }
}
package org.kodejava.example.hibernate.app;

import org.kodejava.example.hibernate.model.Label;

import java.util.Date;

public class InsertDemo {
    public static void main(String[] args) {
        LabelManager manager = new LabelManager();

        // Creates a Label object we are going to stored in the database.
        // We set the name, modified by and modified date information.
        Label label = new Label();
        label.setName("Sony Music");
        label.setCreated(new Date());

        // Call the LabelManager saveLabel method.
        manager.saveLabel(label);
    }
}

We have the code and the mapping file done. To register the mapping file in the Hibernate configuration file you can see the How do I create Hibernate’s SessionFactory? example. The example also tells you how to create the SessionFactoryHelper class to obtain the Hibernate’s SessionFactory.

How do I create Hibernate’s SessionFactory?

When creating an application the use Hibernate to manage our application persistence object we’ll need a SessionFactory. This factory creates or open a session to talk to a database.

To create a SessionFactory we can define the configuration in hibernate.properties, hibernate.cfg.xml or create it programatically. In this example we’ll use the hibernate.cfg.xml configuration file, which is mostly use when creating Hibernate application.

Below is our session configuration files.

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <!-- JDBC connection settings -->
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost/mediadb</property>
        <property name="connection.username">kodejava</property>
        <property name="connection.password">kodejava123</property>

        <!-- JDBC connection pool, use Hibernate internal connection pool -->
        <property name="connection.pool_size">5</property>

        <!-- Defines the SQL dialect used in Hibernate's application -->
        <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>

        <!-- Enable Hibernate's automatic session context management -->
        <property name="current_session_context_class">thread</property>

        <!-- Disable the second-level cache  -->
        <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>

        <!-- Display and format all executed SQL to stdout -->
        <property name="show_sql">true</property>
        <property name="format_sql">true</property>

        <!-- Drop and re-create the database schema on startup -->
        <property name="hbm2ddl.auto">update</property>

        <!-- Mapping to hibernate mapping files -->
        <mapping resource="org/kodejava/example/hibernate/model/Label.hbm.xml"/>
    </session-factory>
</hibernate-configuration>

Now we have the configuration file done, let’s create a helper class that will configure and build the SessionFactory object. This helper will be used in other Hibernate example in this site.

package org.kodejava.example.hibernate.app;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class SessionFactoryHelper {
    private static final SessionFactory sessionFactory;

    static {
        try {
            // Build a SessionFactory object from session-factory config
            // defined in the hibernate.cfg.xml file. In this file we
            // register the JDBC connection information, connection pool,
            // the hibernate dialect that we used and the mapping to our
            // hbm.xml file for each pojo (plain old java object).
            Configuration config = new Configuration();
            sessionFactory = config.configure().buildSessionFactory();
        } catch (Throwable e) {
            System.err.println("Error in creating SessionFactory object."
                    + e.getMessage());
            throw new ExceptionInInitializerError(e);
        }
    }

    /**
     * A static method for other application to get SessionFactory object
     * initialized in this helper class.
     */
    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
}