Akka is a concurrent framework written by Scala.

Here I demonstrate sample application to send emails with Akka and implemented in Java.

Reasons I decided to use Akka framework other than concurrency.

• Built-in configurable supervisor strategy to monitor child workers and decide what policy applies when there is an exception.
• Can reschedule delivery when application throwing some specific exception.
• Use of actor routers and allow them to use actor connection pool.

Here is how to create supervision strategy.

class EmailServiceActor extends UntypedActor { 
 private static SupervisorStrategy strategy = 
 new OneForOneStrategy(10, Duration.create("1 minute"), 
 new Function<Throwable, Directive>() { 
 @Override 
 public Directive apply(Throwable t) { 
 if (t instanceof MessagingException) { 
 return resume(); 
 } else if (t instanceof Exception) { 
 return stop(); 
 } else { 
 return escalate(); 
 } 
 } 
 }); 
 @Override 
 public void onReceive(Object message) { 
 getContext().actorOf(new Props(EmailServiceWorker.class)).tell(message, self()); 
 } 
 @Override 
 public SupervisorStrategy supervisorStrategy() { 
 return strategy; 
 } 
 }

Here is how child worker create

class EmailServiceWorker extends UntypedActor { 
 @Override 
 public void onReceive(Object message) { 
 try { 
 EmailService emailService = new EmailService(); 
 emailService.sendEmail(); 
 } catch (IOException e) { 
 e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates. 
 } catch (MessagingException e) { 
 e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates. 
 } 
 } 
 @Override 
 public void preStart() { 
 // getContext().system().scheduler().scheduleOnce(Duration.create(5, TimeUnit.SECONDS), self(), "emailWorker", getContext().system().dispatcher(), null); 
 } 
 @Override 
 public void postStop() { 
 } 
 }

Sample application – https://github.com/rajithd/email-service-akka