This is a very easy example of Aspect Oriented Programming. Lets add advice (code to run) before the main() executs and when main() finishes. You will see how without cluttering our Main class or our main() method, we can add modular code to run before or after main().

Prereqs

This example assumes you have a development environment installed with at least the following:

• JDK
• AspectJ
• Eclipse (Netbeans would work too)

Step 1 – Create an AspectJ project

1. In Eclipse, choose File | New | Project.
2. Select AspectJ | AspectJ Project.
3. Click Next.
4. Name your project.
   Note: I named my project mainExample
5. Click Finish.

Step 2 – Create a class containing main()

1. Right-click on the project in Package Explorer and choose New | Class.
2. Provide a package name.
   Note: I named my package mainExample, the same as the project name.
3. Give the class a name.
   Note: I often name my class Main.
4. Check the box to include a public static void main(String[] args) method.
5. Click Finish.

package mainExample;

public class MainExample
{
	static void main(String[] args)
	{
		// TODO Auto-generated method stub
	}
}

Step 3 – Create an Aspect object

1. Right-click on the mainExample package in Package Explorer and choose New | Other.
2. Choose AspectJ | Aspect.
3. Click Next.
   Note: The package should already be filled out for you with “mainExample”.
4. Give the Aspect a name.
   Note: I named mine StartEndAspect.
5. Click Finish.

package mainExample;

public aspect StartEndAspect
{

}

Step 4 – Add a pointcut to the StartEndAspect

1. Create a pointcut named mainMethod().
2. Configure the pointcut to use “execution”.
3. Configure the pointcut to be specifically for the “public static void main(String[] args)” method.

package mainExample;

public aspect StartEndAspect
{
    pointcut mainMethod() : execution(public static void main(String[]));
}

Note: Notice that to be specific for a method, you include everything but the parameter name.

Step 5 – Add before advice

1. Add a before() statement for mainMethod().
2. Have it simple write to the console a message such as “The application has started.”

package mainExample;

public aspect StartEndAspect
{
    pointcut mainMethod() : execution(public static void main(String[]));

    before() : mainMethod()
    {
        System.out.println("Application has started...");
    }
}

Step 6 – Add after advice

1. Add an after() statement for mainMethod().
2. Have it simple write to the console a message such as “The application has ended.”

package mainExample;

public aspect StartEndAspect
{
    pointcut mainMethod() : execution(public static void main(String[]));

    before() : mainMethod()
    {
        System.out.println("The application has ended...");
    }

    after() : mainMethod()
    {
        System.out.println("The application has ended...");
    }
}

So the advice is applied and even though there is not code in main(), the advice is applied and the console output is as follows:

The application has started…
The application has ended…

Congratulations you have learned one simple way to use Aspect Orient Programming for Java with AspectJ.
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