org.objectstyle.cayenne.event.EventSubject.java Source code

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Here is the source code for org.objectstyle.cayenne.event.EventSubject.java

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/* ====================================================================
 * 
 * The ObjectStyle Group Software License, version 1.1
 * ObjectStyle Group - http://objectstyle.org/
 * 
 * Copyright (c) 2002-2004, Andrei (Andrus) Adamchik and individual authors
 * of the software. All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 
 * 3. The end-user documentation included with the redistribution, if any,
 *    must include the following acknowlegement:
 *    "This product includes software developed by independent contributors
 *    and hosted on ObjectStyle Group web site (http://objectstyle.org/)."
 *    Alternately, this acknowlegement may appear in the software itself,
 *    if and wherever such third-party acknowlegements normally appear.
 * 
 * 4. The names "ObjectStyle Group" and "Cayenne" must not be used to endorse
 *    or promote products derived from this software without prior written
 *    permission. For written permission, email
 *    "andrus at objectstyle dot org".
 * 
 * 5. Products derived from this software may not be called "ObjectStyle"
 *    or "Cayenne", nor may "ObjectStyle" or "Cayenne" appear in their
 *    names without prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE OBJECTSTYLE GROUP OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 * 
 * This software consists of voluntary contributions made by many
 * individuals and hosted on ObjectStyle Group web site.  For more
 * information on the ObjectStyle Group, please see
 * <http://objectstyle.org/>.
 */

package org.objectstyle.cayenne.event;

import java.util.Map;

import org.apache.commons.collections.map.ReferenceMap;

/**
 * This class encapsulates the String that is used to identify the <em>subject</em> 
 * that a listener is  interested in. Using plain Strings causes several severe
 * problems:
 * <ul>
 * <li>it's easy to misspell a subject, leading to undesired behaviour at
 * runtime that is hard to debug.</li>
 * <li>in systems with many different subjects there is no safeguard for
 * defining the same subject twice for different purposes. This is especially
 * true in a distributed setting.
 * </ul>
 * 
 * @author Dirk Olmes
 * @author Holger Hoffstaette
 */

public class EventSubject extends Object {

    // a Map that will allow the values to be GC'ed
    private static Map _registeredSubjects = new ReferenceMap(ReferenceMap.HARD, ReferenceMap.WEAK);

    // Subject identifier in the form "com.foo.bar/SubjectName"
    private String _fullyQualifiedSubjectName;

    /**
     * Returns an event subject identified by the given owner and subject name.
     * 
     * @param subjectOwner the Class used for uniquely identifying this subject
     * @param subjectName a String used as name, e.g. "MyEventTopic"
     * @throws IllegalArgumentException if subjectOwner/subjectName are
     * <code>null</code> or subjectName is empty.
     */
    public static EventSubject getSubject(Class subjectOwner, String subjectName) {
        if (subjectOwner == null) {
            throw new IllegalArgumentException("Owner class must not be null.");
        }

        if ((subjectName == null) || (subjectName.length() == 0)) {
            throw new IllegalArgumentException("Subject name must not be null or empty.");
        }

        String fullSubjectName = subjectOwner.getName() + "/" + subjectName;
        EventSubject newSubject = (EventSubject) _registeredSubjects.get(fullSubjectName);
        if (newSubject == null) {
            newSubject = new EventSubject(fullSubjectName);
            _registeredSubjects.put(newSubject.getSubjectName(), newSubject);
        }

        return newSubject;
    }

    /**
     * Private constructor to force use of #getSubject(Class, String)
     */
    private EventSubject() {
    }

    /**
     * Protected constructor for new subjects.
     * 
     * @param fullSubjectName the name of the new subject to be created
     */
    protected EventSubject(String fullSubjectName) {
        super();
        _fullyQualifiedSubjectName = fullSubjectName;
    }

    public boolean equals(Object obj) {
        if (obj instanceof EventSubject) {
            return _fullyQualifiedSubjectName.equals(((EventSubject) obj).getSubjectName());
        }

        return false;
    }

    public int hashCode() {
        return (super.hashCode() ^ _fullyQualifiedSubjectName.hashCode());
    }

    public String getSubjectName() {
        return _fullyQualifiedSubjectName;
    }

    /**
     * @return a String in the form
     * <code>&lt;ClassName 0x123456&gt; SomeName</code>
     * 
     * @see Object#toString()
     */
    public String toString() {
        StringBuffer buf = new StringBuffer(64);

        buf.append("<");
        buf.append(this.getClass().getName());
        buf.append(" 0x");
        buf.append(Integer.toHexString(System.identityHashCode(this)));
        buf.append("> ");
        buf.append(_fullyQualifiedSubjectName);

        return buf.toString();
    }

}