如何使用Java ExecutorService進行任務的重試機制

在Java中，使用ExecutorService進行任務的重試機制可以通過以下幾個步驟實現：

1. 創建一個ExecutorService實例：

ExecutorService executorService = Executors.newFixedThreadPool(5);

2. 定義一個任務類，實現Callable接口。在這個類中，你可以處理任務執行的邏輯，并在遇到異常時拋出異常。

public class RetryableTask<T> implements Callable<T> {
    private final int maxRetries;
    private final int retryDelay;
    private final Supplier<T> taskSupplier;

    public RetryableTask(int maxRetries, int retryDelay, Supplier<T> taskSupplier) {
        this.maxRetries = maxRetries;
        this.retryDelay = retryDelay;
        this.taskSupplier = taskSupplier;
    }

    @Override
    public T call() throws Exception {
        int retries = 0;
        while (retries < maxRetries) {
            try {
                return taskSupplier.get();
            } catch (Exception e) {
                retries++;
                if (retries >= maxRetries) {
                    throw e;
                }
                Thread.sleep(retryDelay);
            }
        }
        return null;
    }
}

3. 創建一個方法來提交任務并獲取結果。在這個方法中，你可以捕獲ExecutionException，然后從中獲取原始異常，并根據需要重試任務。

public <T> T submitWithRetry(RetryableTask<T> task) {
    int maxRetries = 3;
    int retryDelay = 1000; // 1 second
    int retries = 0;

    while (retries < maxRetries) {
        try {
            return executorService.submit(task).get();
        } catch (InterruptedException | ExecutionException e) {
            retries++;
            if (retries >= maxRetries) {
                throw new RuntimeException("Task failed after " + maxRetries + " retries", e);
            }
            try {
                Thread.sleep(retryDelay);
            } catch (InterruptedException ie) {
                Thread.currentThread().interrupt();
                throw new RuntimeException("Thread interrupted while waiting to retry", ie);
            }
        }
    }
    return null;
}

4. 使用submitWithRetry方法提交任務。

public static void main(String[] args) {
    ExecutorService executorService = Executors.newFixedThreadPool(5);
    RetryableTask<String> task = new RetryableTask<>(3, 1000, () -> {
        // Your task logic here
        if (Math.random() > 0.5) {
            throw new RuntimeException("Random failure");
        }
        return "Task completed successfully";
    });

    String result = submitWithRetry(task);
    System.out.println("Result: " + result);

    executorService.shutdown();
}

在這個示例中，我們創建了一個RetryableTask類，它實現了Callable接口。我們還創建了一個submitWithRetry方法，用于提交任務并處理重試邏輯。當任務失敗時，submitWithRetry方法會根據指定的重試次數和延遲時間進行重試。如果任務在重試次數內仍然失敗，submitWithRetry方法會拋出一個運行時異常。