java告诉ThreadPoolExecutor何时应该进行或不进行

Question

我必须通过某个端口向几台计算机发送一组文件。事实上，每次调用发送文件的方法时，都会计算目标数据（地址和端口）。因此，使用为每个方法调用创建线程的循环，并使用BindException的try-catch语句包围方法调用，以处理程序试图使用已在使用的端口（不同的目标地址可能通过同一端口接收消息）的情况，告知线程等待几秒钟，然后重新启动以重试，并继续尝试，直到未引发异常（成功执行传送）。 我不知道为什么（虽然我第一次看到它时可以猜到），Netbeans警告我在循环中休眠线程对象不是最佳选择。然后我在谷歌上搜索了一些进一步的信息，找到了this link to another stackoverflow post, which looked so interesting（我从来没有听说过the ThreadPoolExecutor class）。为了改进我的程序，我一直在阅读这个链接和API，但是我还不确定我应该如何在我的程序中应用它。谁能帮我一把吗

编辑：重要代码：

        for (Iterator<String> it = ConnectionsPanel.list.getSelectedValuesList().iterator(); it.hasNext();) {
        final String x = it.next();
        new Thread() {

            @Override
            public void run() {
                ConnectionsPanel.singleAddVideos(x);
            }
        }.start();
    }

    private static void singleAddVideos(String connName) {
    String newVideosInfo = "";

    for (Iterator<Video> it = ConnectionsPanel.videosToSend.iterator(); it.hasNext();) {
        newVideosInfo = newVideosInfo.concat(it.next().toString());
    }

    try {
        MassiveDesktopClient.sendMessage("hi", connName);
        if (MassiveDesktopClient.receiveMessage(connName).matches("hello")) {
            MassiveDesktopClient.sendMessage(newVideosInfo, connName);
        }
    } catch (BindException ex) {
        MassiveDesktopClient.println("Attempted to use a port which is already being used. Waiting and retrying...", new Exception().getStackTrace()[0].getLineNumber());
        try {
            Thread.sleep(MassiveDesktopClient.PORT_BUSY_DELAY_SECONDS * 1000);
        } catch (InterruptedException ex1) {
            JOptionPane.showMessageDialog(null, ex1.toString(), "Error", JOptionPane.ERROR_MESSAGE);
        }
        ConnectionsPanel.singleAddVideos(connName);
        return;
    }

    for (Iterator<Video> it = ConnectionsPanel.videosToSend.iterator(); it.hasNext();) {
        try {
            MassiveDesktopClient.sendFile(it.next().getAttribute("name"), connName);
        } catch (BindException ex) {
            MassiveDesktopClient.println("Attempted to use a port which is already being used. Waiting and retrying...", new Exception().getStackTrace()[0].getLineNumber());
            try {
                Thread.sleep(MassiveDesktopClient.PORT_BUSY_DELAY_SECONDS * 1000);
            } catch (InterruptedException ex1) {
                JOptionPane.showMessageDialog(null, ex1.toString(), "Error", JOptionPane.ERROR_MESSAGE);
            }
            ConnectionsPanel.singleAddVideos(connName);
            return;
        }
    }
}

Answer 1

你的问题不是很清楚——我知道你想重新运行你的任务，直到它成功（没有例外）。要做到这一点，你可以：

• 尝试在不捕获异常的情况下运行代码
• 捕捉未来的例外
• 如果任务失败，请稍后重新安排任务

一个简化的代码如下-添加错误消息并根据需要进行优化：

public static void main(String[] args) throws Exception {
    ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(corePoolSize);
    final String x = "video";
    Callable<Void> yourTask = new Callable<Void>() {
        @Override
        public Void call() throws BindException {
            ConnectionsPanel.singleAddVideos(x);
            return null;
        }
    };
    Future f = scheduler.submit(yourTask);
    boolean added = false; //it will retry until success
                           //you might use an int instead to retry
                           //n times only and avoid the risk of infinite loop
    while (!added) {
        try {
            f.get();
            added = true; //added set to true if no exception caught
        } catch (ExecutionException e) {
            if (e.getCause() instanceof BindException) {
                scheduler.schedule(yourTask, 3, TimeUnit.SECONDS); //reschedule in 3 seconds
            } else {
                //another exception was thrown => handle it
            }
        }
    }
}

public static class ConnectionsPanel {

    private static void singleAddVideos(String connName) throws BindException {
        String newVideosInfo = "";

        for (Iterator<Video> it = ConnectionsPanel.videosToSend.iterator(); it.hasNext();) {
            newVideosInfo = newVideosInfo.concat(it.next().toString());
        }

        MassiveDesktopClient.sendMessage("hi", connName);
        if (MassiveDesktopClient.receiveMessage(connName).matches("hello")) {
            MassiveDesktopClient.sendMessage(newVideosInfo, connName);
        }

        for (Iterator<Video> it = ConnectionsPanel.videosToSend.iterator(); it.hasNext();) {
            MassiveDesktopClient.sendFile(it.next().getAttribute("name"), connName);
        }
    }
}