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Spring Retry provides an abstraction around retrying failed operations, with an emphasis on declarative control of the process and policy-based bahaviour that is easy to extend and customize. For instance, you can configure a plain POJO operation to retry if it fails, based on the type of exception, and with a fixed or exponential backoff.
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/*
 * Copyright 2006-2012 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.retry.backoff;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.retry.RetryContext;
import org.springframework.util.ClassUtils;

/**
 * Implementation of {@link BackOffPolicy} that increases the back off period
 * for each retry attempt in a given set using the {@link Math#exp(double)
 * exponential} function.
 * 
 * This implementation is thread-safe and suitable for concurrent access.
 * Modifications to the configuration do not affect any retry sets that are
 * already in progress.
 * 
 * The {@link #setInitialInterval(long)} property controls the initial value
 * passed to {@link Math#exp(double)} and the {@link #setMultiplier(double)}
 * property controls by how much this value is increased for each subsequent
 * attempt.
 * 
 * @author Rob Harrop
 * @author Dave Syer
 * @author Gary Russell
 */
public class ExponentialBackOffPolicy implements SleepingBackOffPolicy {

	protected final Log logger = LogFactory.getLog(this.getClass());
	/**
	 * The default 'initialInterval' value - 100 millisecs. Coupled with the
	 * default 'multiplier' value this gives a useful initial spread of pauses
	 * for 1-5 retries.
	 */
	public static final long DEFAULT_INITIAL_INTERVAL = 100L;

	/**
	 * The default maximum backoff time (30 seconds).
	 */
	public static final long DEFAULT_MAX_INTERVAL = 30000L;

	/**
	 * The default 'multiplier' value - value 2 (100% increase per backoff).
	 */
	public static final double DEFAULT_MULTIPLIER = 2;

	/**
	 * The initial sleep interval.
	 */
	private volatile long initialInterval = DEFAULT_INITIAL_INTERVAL;

	/**
	 * The maximum value of the backoff period in milliseconds.
	 */
	private volatile long maxInterval = DEFAULT_MAX_INTERVAL;

	/**
	 * The value to increment the exp seed with for each retry attempt.
	 */
	private volatile double multiplier = DEFAULT_MULTIPLIER;

	private Sleeper sleeper = new ObjectWaitSleeper();

	/**
	 * Public setter for the {@link Sleeper} strategy.
	 * @param sleeper the sleeper to set defaults to {@link ObjectWaitSleeper}.
	 */
	public void setSleeper(Sleeper sleeper) {
		this.sleeper = sleeper;
	}

    public ExponentialBackOffPolicy withSleeper(Sleeper sleeper) {
        ExponentialBackOffPolicy res = newInstance();
        cloneValues(res);
        res.setSleeper(sleeper);
        return res;
    }

    protected ExponentialBackOffPolicy newInstance() {
        return new ExponentialBackOffPolicy();
    }

    protected void cloneValues(ExponentialBackOffPolicy target) {
        target.setInitialInterval(getInitialInterval());
        target.setMaxInterval(getMaxInterval());
        target.setMultiplier(getMultiplier());
        target.setSleeper(sleeper);
    }

	/**
	 * Set the initial sleep interval value. Default is 100
	 * millisecond. Cannot be set to a value less than one.
	 */
	public void setInitialInterval(long initialInterval) {
		this.initialInterval = (initialInterval > 1 ? initialInterval : 1);
	}

	/**
	 * Set the multiplier value. Default is '2.0'. Hint: do not use
	 * values much in excess of 1.0 (or the backoff will get very long very
	 * fast).
	 */
	public void setMultiplier(double multiplier) {
		this.multiplier = (multiplier > 1.0 ? multiplier : 1.0);
	}

	/**
	 * Setter for maximum back off period. Default is 30000 (30 seconds). the
	 * value will be reset to 1 if this method is called with a value less than
	 * 1. Set this to avoid infinite waits if backing off a large number of
	 * times (or if the multiplier is set too high).
	 * 
	 * @param maxInterval in milliseconds.
	 */
	public void setMaxInterval(long maxInterval) {
		this.maxInterval = maxInterval > 0 ? maxInterval : 1;
	}

	/**
	 * The initial period to sleep on the first backoff.
	 * @return the initial interval
	 */
	public long getInitialInterval() {
		return initialInterval;
	}

	/**
	 * The maximum interval to sleep for. Defaults to 30 seconds.
	 * 
	 * @return the maximum interval.
	 */
	public long getMaxInterval() {
		return maxInterval;
	}

	/**
	 * The multiplier to use to generate the next backoff interval from the
	 * last.
	 * 
	 * @return the multiplier in use
	 */
	public double getMultiplier() {
		return multiplier;
	}

	/**
	 * Returns a new instance of {@link BackOffContext} configured with the
	 * 'expSeed' and 'increment' values.
	 */
	public BackOffContext start(RetryContext context) {
		return new ExponentialBackOffContext(this.initialInterval, this.multiplier, this.maxInterval);
	}

	/**
	 * Pause for a length of time equal to '
	 * exp(backOffContext.expSeed)'.
	 */
	public void backOff(BackOffContext backOffContext) throws BackOffInterruptedException {
		ExponentialBackOffContext context = (ExponentialBackOffContext) backOffContext;
		try {
			long sleepTime = context.getSleepAndIncrement();
			if (logger.isDebugEnabled()) {
				logger.debug("Sleeping for " + sleepTime);
			}
			sleeper.sleep(sleepTime);
		}
		catch (InterruptedException e) {
			throw new BackOffInterruptedException("Thread interrupted while sleeping", e);
		}
	}

    static class ExponentialBackOffContext implements BackOffContext {

		private final double multiplier;

		private long interval;

		private long maxInterval;

		public ExponentialBackOffContext(long expSeed, double multiplier, long maxInterval) {
			this.interval = expSeed;
			this.multiplier = multiplier;
			this.maxInterval = maxInterval;
		}

        public synchronized long getSleepAndIncrement() {
            long sleep = this.interval;
            if (sleep > maxInterval) {
                sleep = (long) maxInterval;
            }
            else {
                this.interval = getNextInterval();
            }
            return sleep;
        }

        protected long getNextInterval() {
            return (long)(this.interval * this.multiplier);
        }

        public double getMultiplier() {
            return multiplier;
        }

        public long getInterval() {
            return interval;
        }

        public long getMaxInterval() {
            return maxInterval;
        }
	}

	public String toString() {
		return ClassUtils.getShortName(getClass()) + "[initialInterval=" + initialInterval + ", multiplier="
				+ multiplier + ", maxInterval=" + maxInterval + "]";
	}

}