使用Java ExecutorService如何监控任务执行情况

要监控Java中ExecutorService任务执行情况，您可以采取以下几种方法：

1. 使用Future对象：

当您提交一个任务给ExecutorService时，它会返回一个Future对象。您可以通过这个对象来查询任务的状态和结果。例如：

ExecutorService executor = Executors.newFixedThreadPool(5);
Future<?> future = executor.submit(() -> {
    // Your task code here
});

// Check if the task is done
if (future.isDone()) {
    System.out.println("Task completed.");
} else {
    System.out.println("Task is still running.");
}

// Get the result of the task (if it's a Callable task)
try {
    Object result = future.get();
    System.out.println("Task result: " + result);
} catch (InterruptedException | ExecutionException e) {
    e.printStackTrace();
}

2. 使用CompletionService：

CompletionService可以帮助您在任务完成时获取结果，而无需显式地检查每个任务的状态。这可以让您更有效地处理已完成的任务。例如：

ExecutorService executor = Executors.newFixedThreadPool(5);
CompletionService<Integer> completionService = new ExecutorCompletionService<>(executor);

for (int i = 0; i < 10; i++) {
    completionService.submit(() -> {
        // Your task code here
        return i * 2;
    });
}

for (int i = 0; i < 10; i++) {
    try {
        Future<Integer> completedFuture = completionService.take();
        System.out.println("Task result: " + completedFuture.get());
    } catch (InterruptedException | ExecutionException e) {
        e.printStackTrace();
    }
}

3. 使用CountDownLatch：

CountDownLatch是一个同步辅助类，允许一个或多个线程等待直到一组操作完成。您可以使用CountDownLatch来监控任务何时完成。例如：

ExecutorService executor = Executors.newFixedThreadPool(5);
CountDownLatch latch = new CountDownLatch(10);

for (int i = 0; i < 10; i++) {
    executor.submit(() -> {
        try {
            // Your task code here
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            latch.countDown();
        }
    });
}

try {
    latch.await();
    System.out.println("All tasks completed.");
} catch (InterruptedException e) {
    e.printStackTrace();
}

4. 使用ScheduledExecutorService：

如果您需要定期检查任务执行情况，可以使用ScheduledExecutorService来安排一个定时任务，该任务会查询任务的状态。例如：

ExecutorService executor = Executors.newFixedThreadPool(5);
ScheduledExecutorService monitorExecutor = Executors.newScheduledThreadPool(1);

Future<?> future = executor.submit(() -> {
    // Your task code here
});

monitorExecutor.scheduleAtFixedRate(() -> {
    if (future.isDone()) {
        System.out.println("Task completed.");
    } else {
        System.out.println("Task is still running.");
    }
}, 0, 10, TimeUnit.SECONDS);

请注意，这些方法仅提供任务执行情况的有限监控。如果您需要更详细的监控，您可能需要考虑使用Java的内置监控和日志记录工具，或者使用第三方库来监控和管理ExecutorService。