1001 Computer

This tutorial will show the possibilities of JPA and Java SE on the basis of a simple example.
The IDE used for coding is Netbeans 6.5 .

Expenditure of time: ~ 15 minutes.

A working MySQL installation is required. First we create a MySQL example database called “jpa_demo”.

Choose Window -> Services and click. The following window should open now:

Simply rightclick on SQL-Server, then choose “Create Database”, in the following dialog enter “jpa_demo” (without quotes)

and the database is created.

Make a new project named JPAJavaSE from the category “Java” and select Java application:

For the moment we ignore the created “Main” class and make a new class “Computer” in our project.
Press Ctrl+n (fastest way) the “New File” window opens, choose “Entity Class” from the category “Persistence”.

Choose “Computer” as the class name and create a persistence unit with these settings:

Netbeans creates an entity class, edit it until it looks like this:

package jpajavase;

import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Computer implements Serializable
{
    private Long id;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public Long getId()
    {
        return id;
    }

    public void setId(Long id)
    {
        this.id = id;
    }
}

package jpajavase2;

import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Computer implements Serializable
{
    private Long id;
    private String model;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public Long getId()
    {
        return id;
    }

    public void setId(Long id)
    {
        this.id = id;
    }

    public String getModel()
    {
        return model;
    }

    public void setModel(String model)
    {
        this.model = model;
    }
}

The “persistence.xml” generated by Netbeans can be used without any changes in this example.
For everything working as expected we need the MySQL driver, so let’s import the library:
Rightclick on project, choose “Properties”.
Select categories, then libraries:

Choose “Add Library” and scroll down until you see “MySQL JDBC Driver”:

With “Add Library” we add the driver to our project. Ok, we’re done.

Last but not least:

Our good ol’ Main class:

package jpajavase;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;

public class Main
{
    public static void main(String[] args)
    {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("JPAJavaSE_PU");
        EntityManager em = emf.createEntityManager();

        Computer comp = new Computer();
        comp.setModelName("JavaCodersDarling");

        EntityTransaction trans = em.getTransaction();

        trans.begin();
        em.persist(comp);
        trans.commit();
    }
}

We need to create the EntityManagerFactory by ourselves, if we use JEE the application server does this.
Get an EntityManager from the Factory, tinker a Computer object and an EntityTransaction.

With

trans.begin();
em.persist(comp);
trans.commit();

our Computer should now be in the database. Attention: exceptions may fly here, i have ignored them for simplicity of code.

Press F6 and Netbeans creates the project.

Let’s check if our computer is really in the database: open the “Services” window:

Rightclick on our computer in the tables, choose “View Data” and the following window should appear:

That’s all.
That was simple, wasn’t it?

Tags: Java, Netbeans