在java中将听众转变为未来

Question

我试图将一个监听器变成一个Future,用于异步连接.我不习惯使用java期货,我有一些javascript承诺的经验,但我没有看到如何在java中编写它(我在Java 8中看到"CompletableFuture"可以解决我的问题,不幸的是我是坚持使用java 7).这是我到目前为止所做的:

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();
        }   
    }
}

我找不到任何简单的方法来做到这一点.到目前为止,我发现的唯一解决方案是扩展FutureTask并在Callable运行结束时等待/休眠,直到某个状态变量设置为已解决.我真的不喜欢在我的业务代码中等待/休眠的想法,可能有一些已经存在的东西让它延期了？(在java中,还是像Apache commons或guava这样的流行库？)

Answer 1

我终于得到了同事的回答.我正在寻找的是Guava:SettableFuture.这是代码的样子:

    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;