在java中将听众转变为未来 [英] Turning a listener into a future in java

问题描述

我正在尝试将侦听器转换为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可能解决了我的问题，不幸的是我是坚持java 7）。以下是我到目前为止所做的事情：

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();
        }   
    }
}

我找不到任何简单的方法。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，可能存在一些已经存在的东西使其延迟？ （在java中，还是像Apache commons或guava这样的流行库？）

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?)

推荐答案

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

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;

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