Aspect Oriented Programming: Java EE

CDI is a part of the Java EE farmework which provides us with AOP.

This example is the same one with the spirng aop example post. I will display the behaviour of two beans with the same definition but each one has a different aspect, more specific they will use a different interceptor.

The Entered annotation would be our interceptor binding

package com.gkatzioura;

import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import javax.interceptor.InterceptorBinding;

@Inherited
@InterceptorBinding
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD,ElementType.TYPE})
public @interface Entered {
    
}

The employee interface will be used to create the beans for this project.

package com.gkatzioura;

import javax.ejb.Local;
import javax.ejb.Singleton;

@Local
public interface Employee {
    
    @Entered
    public void enterWorkArea();
    
}

We will have two different kind of advices.
The SupervisorBeforeAdvice

package com.gkatzioura;

import java.io.Serializable;
import java.util.logging.Logger;
import javax.interceptor.AroundInvoke;
import javax.interceptor.Interceptor;
import javax.interceptor.InvocationContext;

@Entered
@Interceptor
public class SupervisorBeforeAdvice implements Serializable{
    
    private static final Logger LOGGER = Logger.getLogger(SupervisorBeforeAdvice.class.toString());
    
    @AroundInvoke
    protected Object protocolInvocation(final InvocationContext invocationContext) throws Exception {

        if(invocationContext.getMethod().getName().equals("enterWorkArea")) {
            LOGGER.info("Check if everything is ok");
        }
        
        return invocationContext.proceed();
    }
    
}

And the WorkerBeforeAdvice

package com.gkatzioura;

import java.io.Serializable;
import java.util.logging.Logger;
import javax.interceptor.AroundInvoke;
import javax.interceptor.Interceptor;
import javax.interceptor.InvocationContext;

@Entered
@Interceptor
public class WorkerBeforeAdvice implements Serializable {
    
    private static final Logger LOGGER = Logger.getLogger(WorkerBeforeAdvice.class.toString());
    
    @AroundInvoke
    protected Object protocolInvocation(final InvocationContext invocationContext) throws Exception {
        
        if(invocationContext.getMethod().getName().equals("enterWorkArea")) {
            LOGGER.info("Informing the supervisor that I have arrived");
        }
        
        return invocationContext.proceed();
    }
    
}

Two different beans will implement our employee interface.

Supervisor

package com.gkatzioura;

import javax.ejb.Stateless;
import javax.interceptor.Interceptors;

@Stateless
public class SupervisorEmployee implements Employee{

    @Override
    @Interceptors(SupervisorBeforeAdvice.class)
    public void enterWorkArea() {
    
    }
    
}

And worker

package com.gkatzioura;

import javax.ejb.Stateless;
import javax.interceptor.Interceptors;

@Stateless
public class WorkerEmployee implements Employee{

    @Override
    @Interceptors(WorkerBeforeAdvice.class)
    public void enterWorkArea() {
    }
    
}

I will use JAX-RS to cal those beans

Application configuration

package com.gkatzioura.jersey;

import javax.ws.rs.core.Application;

@javax.ws.rs.ApplicationPath("rest")
public class ApplicationConfig extends Application {

}

And calling the two beans from different endpoints

package com.gkatzioura.jersey;


import com.gkatzioura.Employee;
import com.gkatzioura.SupervisorBeforeAdvice;
import com.gkatzioura.WorkerBeforeAdvice;
import javax.ejb.EJB;
import javax.interceptor.Interceptors;
import javax.ws.rs.GET;
import javax.ws.rs.Path;

@Path("/")
public class AspectEndpoint {
    
    @EJB(beanName = "WorkerEmployee")
    Employee worker;
    
    @EJB(beanName = "SupervisorEmployee")
    Employee supervisor;
    
    @GET
    @Path("/worker/enter")
    public String workerEnter() {
        worker.enterWorkArea();
        return "worker entered";
    }
    
    @GET
    @Path("/supervisor/enter")
    public String supervisorEnter() {
        supervisor.enterWorkArea();
        return "supervisor entered";
    }
    
}