Great Lesson!

1. Choose the JAR with the drivers according to your oracle’s database version and put in the lib/ directory of your web application
2. Configure your application.conf file,  located inside the conf/ directory
   • In the JPA Configuration Section you have to choose the JPA (Hibernate) dialect. In my case I was working with oracle10g so i had to insert in the configuration file:

     • jpa.dialect=org.hibernate.dialect.Oracle10gDialect

   • Now you just need to add the following lines, according to your database (including username and password).

     • db.url=jdbc:oracle:thin:@yourdatabaseserver:1521:dbname
       db.driver=oracle.jdbc.driver.OracleDriver
       db.user=yourusername
       db.pass=yourpassword

3. Now you just need to restart the server. He adds the database drivers automatically to the classpath of the project.
4. If you want, you can generate Netbeans or Eclipse projects, so you can open this projects with everything configured.

Really easy with no XMLs!

In every checkbox element I want to send a post message to my Play Framework.

jQuery.each($(':checkbox'), function() {
    $.post('@{myPlayMethod()}', { itemValue: $(this).val() })
});

This code sends the html element value property to method “myPlayMethod(String itemValue)“.

What about dividing this network application in two layers? One layer, with all the network code and the top layer with only the GUI? How is this possible? Using Java interfaces and the notion of events.

We can start by creating our event interface that will be waken up, when for instance we are receiving a message from the network:

public interface EventNetworkInterface {
	void receiveMessage(String msg);
}

Now it’s time to build our simplified network layer:

public class NetworkLayer {
	EventNetworkInterface gui = null;

	public NetworkLayer(EventNetworkInterface gui) {
		this.gui = gui;
	}

	public void receiveMessageNetwork() {
		//simulates receiving a message from the network
                String msg_received = "Hello World!";
		//wake up event in the GUI
		gui.receiveMessage(msg_received);
	}
}

Now with the network layer created you have to create the GUI:

public class GUI implements EventNetworkInterface {

	public static void main(String[] args) {
		new GUI();
	}

	private NetworkLayer nl;

	public GUI() {
		nl = new NetworkLayer(this);
		//issue a receiveMessage event:
		nl.receiveMessageNetwork();
	}

	@Override
	public void receiveMessage(String msg) {
		System.out.println("I sent the message: " + msg);
	}

}

In the GUI constructor we are simulating a receivedMessage event after we build the network layer and send the GUI that implements the events that will be waken up when a receiveMessage (in this case) happens.

With this approach you can separate the design code, from the processing code and simplify when you are adding more features to the layers beneath you.

If you want to have multiple classes to execute the same events, see more about the observer pattern.

public static Singleton getInstance() {
    if (uniqueInstance == null) {
       uniqueInstance = new Singleton();
    }
    return uniqueInstance;
}

In this code snippet, if you have a multithreaded application that executes the same class, some concurrency problems can occur. For instance if the two threads accesses to the condition at the same time, creates two different Singleton instances. How can you fix this problem? Newer virtual machines (like JVM 1.5) ensures this when you create the Singleton instance in a static variable outside of any method. The JVM guarantees that the instance will be created before any thread accesses the static uniqueInstance variable. The solution for this is:

public class Singleton {
    private static Singleton uniqueInstance = new Singleton ();

    private Singleton() {}

    public static Singleton getInstance () {
       return uniqueInstance;
    }
}

“The principle was suggested by management thinker Joseph M. Juran. It was named after the Italian economist Vilfredo Pareto, who observed that 80% of income in Italy was received by 20% of the Italian population. The assumption is that most of the results in any situation are determined by a small number of causes.”

This rule says that 80% of your outcomes come from 20% of your inputs. For instance, in your life, there are certain activities that you do (your 20%) that account for the majority (your 80%) of your happiness and outputs.

The 80/20 rule can be applied to your life and your business, where being happy and satisfied for what you do, is the most important thing. Off course that money is important, but it shouldn’t be so important compared to your happiness.

Live your life following the 80/20 rule. Follow your dream!

(more information about the 80/20 rule)