AspectJ in Scala Example

Question
1

Is there a working example, including the configurations required, available of a project working with Scala and AspectJ please ?

Thanks :slight_smile:

2

Gianluca - that might be a very rare thing.

In Scala we’ll frequently build our own higher-order functions to cover a lot of the use cases for AspectJ. It’s very easy - for example - to write a “whenever I use a database” higher-order function to put general database pre- and post- operations in.

This approach would leave out one of AspectJ’s main use cases: injecting code at point cuts in someone else’s library.

Theoretically using AspectJ should work reasonably well on Scala byte code. I’ve never seen an example.

3

We use AspectJ with Scala all the time. You must use load-time weaving, but it works the same as with Java.

2 Likes
4

Thanks a lot for your help.

Could you kindly provide me with an example project maybe that would highlight the main principles and how to execute it please ?

Thanks a lot and good day :slight_smile:

5

I don’t have an example-project, but really - any example-project in Java will do as long as LTW is concerned, as LTW loads class-files and does the instrumentation at runtime (class load time). There are many examples using Spring and AspectJ, note that you need -javaagent:path/to/spring-instrument.jar for LTW to work.

1 Like
6

Thanks a lot for your help :slight_smile: I’ll try it out :slight_smile: So what I need is only to work like in Java, but instead address the Main Class as for example Main.scala right ?

Thanks a lot and good day :slight_smile:

7

There’s nothing AspectJ-specific about running a program written in Scala vs. Java, as LTW operates on class-files at runtime. If you have any concrete problems it’s best to post the details here.

8

I have these classes (copied them from a book “AspectJ in Action Second Edition” :

SecurityAspect.aj

//Listing 2.3 Aspect to secure access
public aspect SecurityAspect {
	private Authenticator authenticator = new Authenticator();

	pointcut secureAccess() : execution(* MessageCommunicator.deliver(..));

	before() : secureAccess() {
		System.out.println("Checking and authenticating user");
		authenticator.authenticate();
	}
}

Main.java

public class Main {
	public static void main(String[] args) {
		MessageCommunicator messageCommunicator = new MessageCommunicator();
		messageCommunicator.deliver("Wanna learn AspectJ?");
		messageCommunicator.deliver("Harry", "having fun?");
	}
}

MessageCommunicator.java

public class MessageCommunicator {
	public void deliver(String message) {
		System.out.println(message);
	}

	public void deliver(String person, String message) {
		System.out.println(person + ", " + message);
	}
}

Authenticator.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Authenticator {
	private ThreadLocal<String> authenticatedUser = new ThreadLocal<String>();
	
	public void authenticate() {
		if (isAuthenticated()) {
			return;
		}
		String[] userNamePassword = getUserNamePassword();
		if (!userNamePassword[0].equals(userNamePassword[1])) {
			throw new AuthenticationException("User/password didn't match");
		}
		authenticatedUser.set(userNamePassword[0]);
	}
	
	public boolean isAuthenticated() {
		return authenticatedUser.get() != null;
	}
	
	public String[] getUserNamePassword() {
		boolean usePrintln = Boolean.getBoolean("ant.run");
		String[] userNamePassword = new String[2];
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		try {
			if (usePrintln) {
				System.out.println("Username: ");
			} else {
				System.out.print("Username: ");
			}
			userNamePassword[0] = in.readLine().trim();
			if (usePrintln) {
				System.out.println("Password: ");
			} else {
				System.out.print("Password: ");
			}
			userNamePassword[1] = in.readLine().trim();
		} catch (IOException ex) {
			// ignore... will return array of null strings
		}
		return userNamePassword;
	}

}

AuthenticatorException.java

public class MessageCommunicator {
	public void deliver(String message) {
		System.out.println(message);
	}

	public void deliver(String person, String message) {
		System.out.println(person + ", " + message);
      }
}

Now I am trying to use aspectj :

Compiling Commands :

ajc -source 5 *.java *.aj
java (-cp path where Main is) Main

However this error crops up :

Exception in thread "main" java.lang.NoClassDefFoundError: org/aspectj/lang/NoAspectBoundException
        at MessageCommunicator.deliver(MessageCommunicator.java:20)
        at Main.main(Main.java:21)
Caused by: java.lang.ClassNotFoundException: org.aspectj.lang.NoAspectBoundException
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:636)
        at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:182)
        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:519)
        ... 2 more

Could anybody help please ?

Thanks a lot and good day :slight_smile:

9

Not to be rude, but; I suggest you ask AspectJ-specific questions on some AspectJ-forum/mailing-list.

10
11

Thanks a lot everyone :slight_smile: