Turning a listener into a future in java

Question

I'm trying to turn a listener into a Future, for asynchronous connection. I'm not used to using java futures yet, I've some experience with javascript promises but I fail to see how to write it in java (I've seen "CompletableFuture" in Java 8 may solve my problem, unfortunately I'm stuck with java 7). Here's what I've done so far:

public Future<Boolean> checkEmailClientConfiguration(final EmailClientConfiguration config) {
    final Future<Boolean> future = ???;
    // In some other languages I would create a deferred
    Transport transport = null;
    try {
        transport = session.getTransport("smtp");
        transport.addConnectionListener(new ConnectionListener() {
            @Override
            public void opened(ConnectionEvent connectionEvent) {
                System.out.println("!!!opened!!! ; connected=" + ((SMTPTransport) connectionEvent.getSource()).isConnected());
                // HERE I would like to make my future "resolved"
            }

            @Override
            public void disconnected(ConnectionEvent connectionEvent) {
            }

            @Override
            public void closed(ConnectionEvent connectionEvent) {
            }
        });
        transport.connect(config.getMailSMTPHost(),
                          config.getMailSMTPPort(),
                          config.getMailUsername(),
                          config.getMailPassword());
        return future;
    } catch (final MessagingException e) {
        throw e;
    } finally{
        if(transport != null){
            transport.close();
        }   
    }
}

I can't find any easy way to do it. The only solution I've found so far is to extend FutureTask and at the end of the Callable run, wait/sleep until some state variable is set as resolved. I don't really like the idea of waiting/sleeping in my business code, there is probably something that already exist to make it deferred? (in java, or popular libraries such as Apache commons or guava?)

Answer 1

I finally got my answer from a colleague. What I'm looking for exists in Guava: SettableFuture. Here's how the code looks like:

    final SettableFuture<Boolean> future = SettableFuture.create();
    Transport transport = null;
    try {
        transport = session.getTransport("smtp");
        transport.addConnectionListener(new ConnectionListener() {
            @Override
            public void opened(ConnectionEvent connectionEvent) {
                future.set(((SMTPTransport) connectionEvent.getSource()).isConnected());
            }

            @Override
            public void disconnected(ConnectionEvent connectionEvent) {
            }

            @Override
            public void closed(ConnectionEvent connectionEvent) {
            }
        });
        transport.connect(config.getMailSMTPHost(),
                config.getMailSMTPPort(),
                config.getMailUsername(),
                config.getMailPassword());
    } catch (final MessagingException e) {
        future.setException(e);
    } finally{
        if(transport != null){
            transport.close();
        }
    }
    return future;