A trigger for periodic task execution with the added capability to modify runtime the period between polls.

DynamicTrigger.java

package directlabs.integration;

import java.util.Date;
import java.util.concurrent.TimeUnit;

import org.springframework.scheduling.Trigger;
import org.springframework.scheduling.TriggerContext;
import org.springframework.util.Assert;

/**
 * A trigger for periodic task execution with the added capability to modify runtime the period between
 * polls. A desired behavior when you are trying to throttle inbound messages via polling rate.
 * 
 * @author jtedilla
 * @see org.springframework.scheduling.support.PeriodicTrigger
 */
public class DynamicTrigger implements Trigger{
	
	private long period;
	private final TimeUnit timeUnit;
	private volatile long initialDelay = 0;
	private volatile boolean fixedRate = false;

	/**
	 * Create a trigger with the given period in milliseconds.
	 */
	public DynamicTrigger(long period) {
		this(period, null);
	}

	/**
	 * Create a trigger with the given period and time unit. The time unit will
	 * apply not only to the period but also to any 'initialDelay' value, if
	 * configured on this Trigger later via {@link #setInitialDelay(long)}.
	 */
	public DynamicTrigger(long period, TimeUnit timeUnit) {
		Assert.isTrue(period >= 0, "period must not be negative");
		this.timeUnit = (timeUnit != null) ? timeUnit : TimeUnit.MILLISECONDS;
		this.period = this.timeUnit.toMillis(period);
	}

	/**
	 * Specify a new period. Very useful when you try to throttle inbound messages by 
	 * modifying the polling rate.
	 */
	public void setPeriod(long newPeriod){
		this.period = newPeriod;
	}

	/**
	 * Specify the delay for the initial execution. It will be evaluated in
	 * terms of this trigger's {@link TimeUnit}. If no time unit was explicitly
	 * provided upon instantiation, the default is milliseconds. 
	 */
	public void setInitialDelay(long initialDelay) {
		this.initialDelay = this.timeUnit.toMillis(initialDelay);
	}

	/**
	 * Specify whether the periodic interval should be measured between the
	 * scheduled start times rather than between actual completion times.
	 * The latter, "fixed delay" behavior, is the default.
	 */
	public void setFixedRate(boolean fixedRate) {
		this.fixedRate = fixedRate;
	}

	/**
	 * Returns the time after which a task should run again.
	 */
	public Date nextExecutionTime(TriggerContext triggerContext) {
		if (triggerContext.lastScheduledExecutionTime() == null) {
			return new Date(System.currentTimeMillis() + this.initialDelay);
		}
		else if (this.fixedRate) {
			return new Date(triggerContext.lastScheduledExecutionTime().getTime() + this.period);
		}
		return new Date(triggerContext.lastCompletionTime().getTime() + this.period);
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + (fixedRate ? 1231 : 1237);
		result = prime * result + (int) (initialDelay ^ (initialDelay >>> 32));
		result = prime * result + (int) (period ^ (period >>> 32));
		result = prime * result
				+ ((timeUnit == null) ? 0 : timeUnit.hashCode());
		return result;
	}
	
}