RetryTemplate.java

import java.util.concurrent.Callable;
import java.util.concurrent.Future;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

/**
 * Retriable Task, manual solution.
 * 
 * @see <a href="https://stackoverflow.com/a/2759040/3072570">ExecutorService that interrupts tasks after a timeout</a>
 * @see <a href="https://stackoverflow.com/a/4738630/3072570">Retry Task Framework</a>
 * 
 * @author falvojr
 */
public class RetryTemplate<T> {

	private final int attempts;
	private final long timeout;
	
	private int retryCount;

	public RetryTemplate(int attempts, long timeout) {
		this.attempts = attempts;
		this.timeout = timeout;
	}

	public T execute(Callable<T> task) throws Exception {
		final int cores = Runtime.getRuntime().availableProcessors();
		// https://stackoverflow.com/a/14423578/3072570
		// https://stackoverflow.com/a/36748183/3072570
		final ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(cores);
		executor.setRemoveOnCancelPolicy(true);
		try {
			final Future<T> taskFuture = executor.submit(task);
			executor.schedule(() -> {
				if (taskFuture.cancel(true)) {
					throw new RuntimeException("Force catch treatment on task cancel.");
				}
				// If the task could not be cancelled, typically because it has already completed normally.
			}, timeout, TimeUnit.MILLISECONDS);
			final T result = taskFuture.get();
			return result;
		} catch (Exception e) {
			if (++retryCount == attempts) {
				final String messageTemplate = "%d attempts to retry failed at %d ms interval.";
				throw new RetryException(String.format(messageTemplate, attempts, timeout), e);
			} else {
				return execute(task);
			}
		} finally {
			executor.shutdown();
			retryCount = 0;
		}
	}

	public int getRetryCount() {
		return retryCount;
	}

}