timpt.de - QuickHibernate

One day late in 2008 we found that starting with hibernate is not easy - even for experienced Programmers. Against this background I decided to give this documentation - with the intention to provide a SIMPLE start with hibernate. This Document is not to make a proper hibernate project which is using all features and has only the needed jars referenced. It is explicitly opposite to that: The intention is to get quick success, to produce a running project with hibernate and to understand the idea behind that - quick and dirty :-). A minimum of swing knowledge is helpful as we use a simple dialog to write to db.

Used tools:

Fist Step:

Second Step

Copy following jars from download (either from ./ (root) of your downloaded file and/or from ./lib folder you should have the following jars:

Third step create a new Eclipse Project

Log4J

Create in src folder of your project a file named log4j.properties and add the following content

Test class

Create a new Testclass
In Eclipse press (in Menu) File -> new ->Java class and name it Test (case-sensitive).
Paste the following code into the Test class (note that it is directly in src Folder - no packages for simpleness ...)

import java.awt.FlowLayout;


import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;



import javax.swing.JButton;

import javax.swing.JFrame;

import javax.swing.JLabel;

import javax.swing.JTextField;




import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.AnnotationConfiguration;



public class Test extends JFrame {


  private JButton button;

  private JTextField textField;

  private SessionFactory sessionFactory;



  public static void main(String[] args){


    new Test();

  }



  public Test(){

// get a sessionfactory from hibernate on startup - this is needed to get a


    // session later

    try{

// if you do not like annotations, you might configur with xml Files -


// if so, the Factory is a different (Configuration())

      sessionFactory = new AnnotationConfiguration().configure()


          .buildSessionFactory();



    }

    catch(Throwable e){

      throw new ExceptionInInitializerError(e);


    }

    createView();

    createListener();

    pack();

    setVisible(true);


  }



  private void createView(){

    setLayout(new FlowLayout());

    add(textField = new JTextField(6));


    add(button = new JButton("button"));

  }



  private void createListener(){


    button.addActionListener(new ActionListener(){

      public void actionPerformed(ActionEvent arg0){

// in hibernate you usually communicate with DB by


// getting / providing POJOs

        POJO p = new POJO();

        p.setValue(textField.getText());


// take a session

        Session sess = sessionFactory.getCurrentSession();

// Start transaction

        sess.beginTransaction();


        sess.save(p);

// commit transaction

        sess.getTransaction().commit();

      }


    });

  }

}

Java2html

This Test class is just providing a Dialog with a Textbox and a Button.
On start it will set the Sessionfactory for Hibernate Annotations.
In the Actionlistener it will create a POJO (which is a pojo - see next Chapter), sets the value of that POJO and stores it in DB.

Create a POJO

As you can see in source above, communication is done using POJOs - we need to create one.
In eclipse press on File ->New -> Java Class and name it POJO.
Paste the following content in POJO class.

import javax.persistence.Column;


import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.Table;



import org.hibernate.annotations.GenericGenerator;




@Entity

@Table(name = "POJO")

public class POJO {

  @Column(name = "value", length = 60)


  public String getValue(){

    return value;

  }



  public void setValue(String value){


    this.value = value;

  }



  @Id

  @GeneratedValue(generator = "system-uuid")


  @GenericGenerator(name = "system-uuid", strategy = "uuid")

  public String getIdentifier(){

    return identifier;


  }



  public void setIdentifier(String identifier){

    this.identifier = identifier;

  }




  private String value;

  private String identifier;



}

Java2html

As you can see, the POJO is just a POJO - plus some Annotations. Some explanation might help you:

Create a hibernate config

This file is the fix-point for Configuration of hibernate.
It provides the Info how to connect to DB along with the info which File will be mapped (name and relative Path, here not necessary due to all Files are in one folder).
In Eclipse in Menu press on File ->New ->File , name it hibernate.cfg.xml (case sensitive) in the src folder.
Paste the following code in this file:

This will create a Database EACH time you will start the program (due to <property name="hibernate.hbm2ddl.auto">create</property>)
Usually you will use it only on first start up, because it automatically create an empty Database on EVERY Start
Therefore after first start you should change it to <property name="hibernate.hbm2ddl.auto">update</property>
By this only new Columns will be added if you add them to the POJO AND you have annotated them.

Now you might start the program (right-click on Test class and select runas Java Application).

A dialog will be displayed.
You can write something into the textfield and press the button - the content of the textfield will be written into the DB.
You can stop it with eclipse (Terminate button in Console View) - due to simpleness and laziness a Windowadapter is missing.

If you do not trust the results download a db tool (eg. Squirrel) and configure it to connect to db.
Be aware that this is only possible if you will have the Test class NOT running - due to the fact that in the given scenario only one connection to DB is configured.

What now?

If you need more than one POJO, you can create it, annotate id accordingly and add a mapping in hibernate.cfg.xml.
If the Pojo is in a package, add the package in dotted notation e.g. my.package.hib.Person.
Read about the generators in the hibernate documentation!
In my eyes one of the most famous tools for hibernate is the hibernate tools - by which you can reengineer from a database the complete hibernate stuff including annotated Pojos!
If you would like to test it, TAKE A LOOK into COMPATILIBITY MATRIX on Hibernate Homepage, otherwise you will be very soon highly frustrated.
Be aware that for me a one2many annotation did NOT remove the orphan elements, although it was proper annotated.
An alternative to hibernate might be OpenJPA -not Mainstream, but it is an Apache child.

Hibernate for beginners

Introduction