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Base classes for Command Query Responsibility Segregation (CQRS) with Java

There is a newer version: 0.5.0

/**
 * Copyright (C) 2015 Michael Schnell. All rights reserved. 
 * http://www.fuin.org/
 *
 * This library is free software; you can redistribute it and/or modify it under
 * the terms of the GNU Lesser General Public License as published by the Free
 * Software Foundation; either version 3 of the License, or (at your option) any
 * later version.
 *
 * This library is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
 * details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library. If not, see http://www.gnu.org/licenses/.
 */
package org.fuin.cqrs4j;

import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.Semaphore;

import javax.validation.constraints.NotNull;

import org.fuin.objects4j.common.ConstraintViolationException;
import org.fuin.objects4j.common.Contract;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Provides some helper methods.
 */
public final class Cqrs4JUtils {

    /** Classes used for JAX-B serialization. */
    public static final List> JAXB_CLASSES = Collections
	    .unmodifiableList(Arrays.asList(Result.class, ConstraintViolationException.class));

    private static final Logger LOG = LoggerFactory.getLogger(Cqrs4JUtils.class);

    /**
     * Private by intention.
     */
    private Cqrs4JUtils() {
	throw new UnsupportedOperationException();
    }

    /**
     * Tries to acquire a lock and runs the code. If no lock can be acquired,
     * the method terminates immediately without executing anything.
     * 
     * @param lock
     *            Semaphore to use.
     * @param code
     *            Code to run.
     */
    public static void tryLocked(@NotNull final Semaphore lock, @NotNull final Runnable code) {
	Contract.requireArgNotNull("lock", lock);
	Contract.requireArgNotNull("code", code);
	if (lock.tryAcquire()) {
	    try {
		code.run();
	    } finally {
		lock.release();
	    }
	}
    }

    /**
     * Waits until a lock is available and executes the code after it was
     * acquired.
     * 
     * @param lock
     *            Semaphore to use.
     * @param code
     *            Code to run.
     */
    public static void runLocked(@NotNull final Semaphore lock, @NotNull final Runnable code) {
	Contract.requireArgNotNull("lock", lock);
	Contract.requireArgNotNull("code", code);
	try {
	    lock.acquire();
	    try {
		code.run();
	    } finally {
		lock.release();
	    }
	} catch (final InterruptedException ex) { // NOSONAR
	    LOG.warn("Couldn't clear view", ex);
	}
    }

}