Question

我有问题使用线程将一些电子邮件复制到其他文件夹，我的问题是，代码不等待完成工作。

我想通过线程移动消息以加入作业，但我需要等待移动所有消息，所以我该怎么做？

private static void moveMessagesToFolders(List<Message> listMessages, Store store, Set<String> setSender) throws MessagingException {

    HashMap<String, List<Message>> mapMessages = separeteMessagesBySender(listMessages, setSender);

    for (Entry<String, List<Message>> mapMessage : mapMessages.entrySet()) {
        Message[] messageArray = mapMessage.getValue().toArray(new Message[mapMessage.getValue().size()]);
        moveMessagesThread(messageArray, mapMessage, store);
    }
}

private static void moveMessagesThread(Message[] messageArray, Entry<String, List<Message>> mapMessage, Store store) {
    Set<Thread> setThread = createMovimentSetThread(messageArray, mapMessage, store);

    for (Thread thread : setThread) {
        thread.start();
    }
}

private static Set<Thread> createMovimentSetThread(Message[] messageArray, Entry<String, List<Message>> mapMessage, Store store) {

    int [] threadIndexs = MathUtil.generateIndex(messageArray);
    Set<Thread> setThread = new HashSet<>(threadIndexs.length);

    for (int i = 0; i < threadIndexs.length; i++) {
        setThread.add(new ThreadMoveMessages(messageArray, mapMessage, store, threadIndexs[i]));
    }

    return setThread;
}

在我将方法更改为此实现Executor之后。

private static void moveMessagesThread(Message[] messageArray, Entry<String, List<Message>> mapMessage, Store store) {

        int [] threadIndexs = MathUtil.generateIndex(messageArray);
        ExecutorService executor = Executors.newFixedThreadPool(4);

        for (int i = 0; i < 4; i++) {
            executor.execute(new ThreadMoveMessages(messageArray, mapMessage, store, threadIndexs[i]));
        }

        executor.shutdown();
    }

实现类Thread

public class ThreadMoveMessages implements Callable<Boolean> {

    private Entry<String, List<Message>> mapMessage;
    private Store store;
    private Message[] messageArray;
    private static int indexControler;
    private static int indexLimit;

    public ThreadMoveMessages(Message[] messageArray, Entry<String, List<Message>> mapMessage, Store store, int indexEnd) {
        this.messageArray = Arrays.copyOf(messageArray, indexEnd);
        this.indexControler += indexEnd;
        this.indexLimit = indexControler;
        this.mapMessage = mapMessage;
    }

    @Override
    public Boolean call() throws Exception {
        Folder folder = null;
        try {
            folder = this.store.getDefaultFolder().getFolder(this.mapMessage.getKey());
            folder.open(Folder.READ_WRITE);
            folder.appendMessages(this.messageArray);
            EmailUtil.deleteListMessage(this.mapMessage.getValue());
        } catch (MessagingException e) {
            e.printStackTrace();
        }                       
        return true;
    }
}

Answer 1

如果要等待异步计算并等待结果，则应使用Futures和Callables。

实施Callable界面：

class MoveMessages implements Callable<Boolean> {

@Override
public Boolean call() throws Exception {
    boolean success = true;

    // Your implementation here

    return success;
}

}

然后将其提交给Executor并检索Future，在Future上调用get()，您将等到Callable的计算完成。

ExecutorService executor = Executors.newFixedThreadPool(5);

MoveMessages moveMessages = new MoveMessages();
Future<Boolean> submit = executor.submit(moveMessages);

Boolean integer = submit.get(); // Will wait until task is finished

executor.shutdown();

当然，您可以提交更多任务获取所有列表并等待所有内容完成。

修改

好的，首先你说你需要等到所有消息都被移动，所以这种情况的一种方法是使用Future和callable ExecutorService。使用ExecutorService您不需要创建和启动大量新线程。记得创建新的线程生成成本。在您的代码中，您为每个发件人创建了4个新线程，使用ExecutorService您只创建固定数量的线程并为每个发件人重用它们。以下是使用Executors和Futures的示例，请注意ExecutorService创建一次以调用moveMessagesToFolders：

private static ExecutorService executor private static void moveMessagesToFolders(List<Message> listMessages, Store store, Set<String> setSender) throws MessagingException { executor = Executors.newFixedThreadPool(4); HashMap<String, List<Message>> mapMessages = separeteMessagesBySender(listMessages, setSender); for (Map.Entry<String, List<Message>> mapMessage : mapMessages.entrySet()) { Message[] messageArray = mapMessage.getValue().toArray(new Message[mapMessage.getValue().size()]); moveMessagesThread(messageArray, mapMessage, store); } executor.shutdown(); } private static void moveMessagesThread(Message[] messageArray, Map.Entry<String, List<Message>> mapMessage, Store store) { List<Future<Boolean>> futures = createMovimentSetThread(messageArray, mapMessage, store); for (Future<Boolean> future : futures) { try { Boolean success = future.get(); // Will wait to accomplished all submited Callables if(!success) { // Check if all submited callables end succesulfy throw new RuntimeException("Something goes wrong while moving messages"); } } catch (InterruptedException e) { e.printStackTrace(); } catch (ExecutionException e) { e.printStackTrace(); } } } private static List<Future<Boolean>> createMovimentSetThread(Message[] messageArray, Map.Entry<String, List<Message>> mapMessage, Store store) { int [] threadIndexs = MathUtil.generateIndex(messageArray); List<Future<Boolean>> futures = new ArrayList<>(); for (int i = 0; i < threadIndexs.length; i++) { Future<Boolean> submit = executor.submit(new ThreadMoveMessages(messageArray, mapMessage, store, threadIndexs[i])); futures.add(submit); } return futures; }

根据您的评论，使用Fork / Join框架将数组拆分为较小的部分可能是更好的解决方案。在谷歌查看更多信息。一些链接：

http://docs.oracle.com/javase/tutorial/essential/concurrency/forkjoin.html

Java 7: Fork/Join Framework

有问题使用线程将电子邮件复制到javamail中的文件夹

1 个答案: