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EasyStream is a small set of utilities for dealing with streams (InputStreams and OutputStreams). The aim is to ease the use of pipes when they're required. Main features are: * "Convert" an OutputStream to an InputStream. * Count the number of bytes read or wrote to a given stream. * While reading the data from an InputStream copy it to a supplied OutputStream. * Read the content of an InputStream multiple times or seek to a definite position

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package com.gc.iotools.stream.base;

/*
 * Copyright (c) 2008, 2015 Gabriele Contini. This source code is released
 * under the BSD License.
 */

import java.util.List;
import java.util.concurrent.AbstractExecutorService;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

/**
 * This class is responsible of instantiating the right executor given an
 * ExecutionModel.
 *
 * @author Gabriele Contini
 * @since 1.0.2
 * @version $Id: ExecutorServiceFactory.java 576 2015-03-28 00:03:33Z gcontini $
 */
public final class ExecutorServiceFactory {

	/**
	 * Executor that stops after a single execution. Used when a thread per
	 * instance strategy is requested.
	 */
	private static class OneShotThreadExecutor extends
			AbstractExecutorService {
		private final ExecutorService exec = Executors
				.newSingleThreadExecutor();

		@Override
		public boolean awaitTermination(final long timeout,
				final TimeUnit unit) throws InterruptedException {
			return this.exec.awaitTermination(timeout, unit);
		}

		@Override
		public void execute(final Runnable command) {
			this.exec.execute(command);
			shutdown();
		}

		@Override
		public boolean isShutdown() {
			return this.exec.isShutdown();
		}

		@Override
		public boolean isTerminated() {
			return this.exec.isTerminated();
		}

		@Override
		public void shutdown() {
			this.exec.shutdown();
		}

		@Override
		public List shutdownNow() {
			return this.exec.shutdownNow();
		}

		@Override
		public  Future submit(final Callable task) {
			final Future result = this.exec.submit(task);
			shutdown();
			return result;
		}

	}

	/*
	 * Default should be 0 otherwise there are problems stopping application
	 * servers.
	 */
	private static ExecutorService executor = new ThreadPoolExecutor(0, 20,
			5, TimeUnit.SECONDS, new ArrayBlockingQueue(500));

	private static final ExecutorService SINGLE_EXECUTOR = Executors
			.newSingleThreadExecutor();

	/**
	 * Getter for the field executor.
	 *
	 * @param tmodel a {@link com.gc.iotools.stream.base.ExecutionModel} object.
	 * @return a {@link java.util.concurrent.ExecutorService} object.
	 */
	public static ExecutorService getExecutor(final ExecutionModel tmodel) {
		final ExecutorService result;
		switch (tmodel) {
		case THREAD_PER_INSTANCE:
			result = new OneShotThreadExecutor();
			break;
		case STATIC_THREAD_POOL:
			result = ExecutorServiceFactory.executor;
			break;
		case SINGLE_THREAD:
			result = ExecutorServiceFactory.SINGLE_EXECUTOR;
			break;

		default:
			throw new UnsupportedOperationException("ExecutionModel ["
					+ tmodel + "] not supported");
		}
		return result;
	}

	/**
	 * 
	 * Call this method to initialize the ExecutorService that is
	 * used in STATIC_THREAD_POOL execution mode.
	 * 
	 *
	 * @see ExecutionModel#STATIC_THREAD_POOL
	 * @see #setDefaultThreadPoolExecutor(ExecutorService)
	 */
	public static void init() {
		setDefaultThreadPoolExecutor(new ThreadPoolExecutor(0, 20, 5,
				TimeUnit.SECONDS, new ArrayBlockingQueue(500)));
	}

	/**
	 * 
	 * Sets the default ExecutorService returned when this class is invoked
	 * with {@link ExecutionModel#STATIC_THREAD_POOL}.
	 * 
	 * 
	 * It can also be used to initialize the class (for instance for use into
	 * a web application).
	 * 
	 *
	 * @param executor
	 *            ExecutorService for the STATIC_THREAD_POOL model.
	 */
	public static void setDefaultThreadPoolExecutor(
			final ExecutorService executor) {
		ExecutorServiceFactory.executor = executor;
	}

	/**
	 * 
	 * Call this method to finalize the execution queue.
	 * 
	 * 
	 * It is mandatory when you use this library in a container, otherwise the
	 * container doesn't terminate gracefully (for instance you can call it in
	 * a web application context listener
	 * ContextListener.shutdown() ).
	 * 
	 */
	public static void shutDown() {
		executor.shutdown();
	}

	/**
	 * Users should not instantiate this class directly.
	 */
	private ExecutorServiceFactory() {
		// don't instantiate
	}
}