Used to schedule and manage Job implementations.

Scheduler.java

package us.ironbase.job;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

/**
 * Used to schedule and manage {@link Job} implementations.
 * 
 * Each <tt>Scheduler</tt> maintains a registry of {@link Trigger}s
 * which jobs may be associated to. When these triggers are activated
 * the business logic of all related jobs are executed.
 * 
 * @author Thomas Nappo
 */
public class Scheduler {

	/**
	 * This internal map is utilized to associate {@link Job} implementations
	 * with {@link Trigger}s so that they may be executed at 
	 */
	private final Map<Trigger, Job> registry = new HashMap<>();

	/**
	 * This internal executor service is used to schedule {@link Job}s.
	 */
	private final ScheduledExecutorService service;

	/**
	 * Constructs a new scheduler.
	 * @param nThreads The number of threads to provide to {@link #service}.
	 */
	public Scheduler(int nThreads) {
		service = Executors.newScheduledThreadPool(nThreads);
	}

	/**
	 * Constructs a new single-threaded scheduler.
	 */
	public Scheduler() {
		this(1);
	}

	/**
	 * Schedules a {@link Job} by constructing a {@link JobLegacy}
	 * which can be used to schedule the job's logic to be ran.
	 * @param job The <tt>Job</tt> implementation which handles the business logic. 
	 * @return The product <tt>JobLegacy</tt> which should be utilized to configure
	 * the job and then truly schedule it to this scheduler.
	 */
	public JobLegacy schedule(Job job) {
		return new JobLegacy(job, this);
	}

	/**
	 * Schedules a {@link JobLegacy} by using it's attributes for a
	 * {@link ScheduledExecutorService#scheduleWithFixedDelay(Runnable, long, long, TimeUnit)}
	 * call.
	 * @param jobLegacy The <tt>JobLegacy</tt> which contains the configured attributes needed
	 * to use the fucntionality for scheduling provided by the {@link #service}.
	 */
	protected void schedule(final JobLegacy jobLegacy) {
		service.scheduleWithFixedDelay(new Runnable() {
			@Override
			public void run() {
				jobLegacy.getParent().execute();
			}
		}, jobLegacy.getRate(), jobLegacy.getRate(), TimeUnit.MILLISECONDS);
	}

}