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/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright (c) 2012 Oracle and/or its affiliates. All rights reserved.
 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * http://glassfish.java.net/public/CDDL+GPL_1_1.html
 * or packager/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at packager/legal/LICENSE.txt.
 *
 * GPL Classpath Exception:
 * Oracle designates this particular file as subject to the "Classpath"
 * exception as provided by Oracle in the GPL Version 2 section of the License
 * file that accompanied this code.
 *
 * Modifications:
 * If applicable, add the following below the License Header, with the fields
 * enclosed by brackets [] replaced by your own identifying information:
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 * elects to include this software in this distribution under the [CDDL or GPL
 * Version 2] license."  If you don't indicate a single choice of license, a
 * recipient has the option to distribute your version of this file under
 * either the CDDL, the GPL Version 2 or to extend the choice of license to
 * its licensees as provided above.  However, if you add GPL Version 2 code
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 */
package org.glassfish.jersey.internal.util;

import java.io.Serializable;
import java.util.UUID;
import java.util.concurrent.atomic.AtomicReference;

/**
 * Lazily initialized, thread-safe, random UUID. Useful for identifying instances
 * for logging & debugging purposes.
 * 
 * The UUID value gets initialized with the first call to {@link #value()} method.
 * Once initialized, the UUID value stays the same.
 *
 * @author Marek Potociar (marek.potociar at oracle.com)
 */
public class LazyUid implements Serializable {
    private static final long serialVersionUID = 4618609413877136867L;

    private final AtomicReference uid = new AtomicReference();

    /**
     * Return UUID value. The returned value is never {@code null}.
     *
     * @return UUID value.
     */
    public String value() {
        if (uid.get() == null) {
            uid.compareAndSet(null, UUID.randomUUID().toString());
        }

        return uid.get();
    }

    @Override
    public boolean equals(Object that) {
        if (that == null) {
            return false;
        }
        if (getClass() != that.getClass()) {
            return false;
        }
        final LazyUid other = (LazyUid) that;
        return this.value().equals(other.value());
    }

    @Override
    public int hashCode() {
        int hash = 7;
        hash = 73 * hash + this.value().hashCode();
        return hash;
    }

    @Override
    public String toString() {
        return value();
    }
}