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Lets developers make their applications more resilient by adding robust transient fault handling logic. Transient faults are errors that occur because of some temporary condition such as network connectivity issues or service unavailability. Typically, if you retry the operation that resulted in a transient error a short time later, you find that the error has disappeared.

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package com.github.rbuck.retry;

import java.util.Random;
import java.util.concurrent.TimeUnit;

/**
 * Implements truncated binary exponential backoff to calculate retry delay per
 * IEEE 802.3-2008 Section 1. There will be at most ten (10) contention periods
 * of backoff, each contention period whose amount is equal to the delta backoff.
 *
 * @author Robert Buck ([email protected])
 */
public class ExponentialBackoff implements RetryStrategy {

    public static final int DEFAULT_RETRY_COUNT = 10;
    public static final long DEFAULT_MIN_BACKOFF = TimeUnit.MILLISECONDS.convert(1, TimeUnit.SECONDS);
    public static final long DEFAULT_MAX_BACKOFF = TimeUnit.MILLISECONDS.convert(30, TimeUnit.SECONDS);
    public static final long DEFAULT_SLOT_TIME = TimeUnit.MILLISECONDS.convert(2, TimeUnit.SECONDS);

    private final Random random = new Random(1);
    private final int maxRetries;
    private final long minBackoff;
    private final long maxBackoff;
    private final long slotTime;
    private int retryCount;

    public ExponentialBackoff() {
        this(DEFAULT_RETRY_COUNT, DEFAULT_MIN_BACKOFF, DEFAULT_MAX_BACKOFF, DEFAULT_SLOT_TIME);

    }

    public ExponentialBackoff(int maxRetries, long minBackoff, long maxBackoff, long slotTime) {
        this.maxRetries = maxRetries;
        this.minBackoff = minBackoff;
        this.maxBackoff = maxBackoff;
        this.slotTime = slotTime;
    }

    public ExponentialBackoff(int maxRetries) {
        this(maxRetries, DEFAULT_MIN_BACKOFF, DEFAULT_MAX_BACKOFF, DEFAULT_SLOT_TIME);
    }

    @Override
    public boolean permitsRetry() {
        if (retryCount < maxRetries) {
            retryCount++;
            return true;
        }
        return false;

    }

    @Override
    public long getRetryDelay() {
        final int MAX_CONTENTION_PERIODS = 10;
        return retryCount == 0 ? 0 : Math.min(minBackoff + random.nextInt(2 << Math.min(retryCount, MAX_CONTENTION_PERIODS - 1)) * slotTime, maxBackoff);
    }

    @Override
    public int getRetryCount() {
        return retryCount;
    }

}