Application: gvSIG desktop » Library: org.gvsig.tools

/* gvSIG. Geographic Information System of the Valencian Government

 *

 * Copyright (C) 2007-2008 Infrastructures and Transports Department

 * of the Valencian Government (CIT)

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License

 * as published by the Free Software Foundation; either version 2

 * of the License, or (at your option) any later version.

 *

 * This program 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 General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,

 * MA  02110-1301, USA.

 *

 */

/*

 * AUTHORS (In addition to CIT):

 * 2008 IVER T.I. S.A.   {{Task}}

 */

package org.gvsig.tools.observer.impl;

import java.lang.ref.Reference;

import java.lang.ref.WeakReference;

import java.util.ArrayList;

import java.util.Iterator;

import java.util.List;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

import org.gvsig.tools.observer.ComplexObserver;

import org.gvsig.tools.observer.ComplexWeakReferencingObservable;

import org.gvsig.tools.observer.Observer;

import org.gvsig.tools.observer.WeakReferencingObservable;

import org.gvsig.tools.visitor.Visitor;

/**

 * Implementation for observers based on the use of Reference, instead of direct

 * Observer references.

 *

 * This way an Observer may be Garbagge collected if its unique reference is the

 * one registered into the Observable.

 *

 * @author <a href="mailto:josemanuel.vivo@iver.es">Jos? Manuel Viv?</a>

 * @author <a href="mailto:cordin@disid.com">C?sar Ordi?ana</a>

 */

public class BaseWeakReferencingObservable implements

                ComplexWeakReferencingObservable, Cloneable {

    private static final Logger LOG = 

        LoggerFactory.getLogger(BaseWeakReferencingObservable.class);

    private boolean propageNotifications = true;

    private DefaultComplexNotification complexNotification = null;

    private boolean changed = false;

    private List obs = new ArrayList();

        private int inComplexCount = 0;

    /**

     * Adds an observer to the set of observers for this object, provided that

     * it is not the same as some observer already in the set. The order in

     * which notifications will be delivered to multiple observers is not

     * specified. See the class comment.

     *

     * @param observer

     *            an observer to be added.

     * @throws NullPointerException

     *             if the parameter o is null.

     */

    public void addObserver(Observer observer) {

        addObserver(new WeakReference(observer));

    }

    public void addObserver(Reference ref) {

        if (ref == null || ref.get() == null) {

            throw new NullPointerException();

        }

        Observer observer = (Observer) ref.get();

        synchronized (obs) {

            if (!contains(observer)) {

                obs.add(ref);

            }

        }

    }

    public void addObservers(BaseWeakReferencingObservable observable) {

        observable.clearDeadReferences();

        Iterator iter = observable.obs.iterator();

        while (iter.hasNext()) {

            addObserver((Reference) iter.next());

        }

    }

    /**

     * Deletes an observer from the set of observers of this object. Passing

     * <CODE>null</CODE> to this method will have no effect.

     *

     * @param observer

     *            the observer to be deleted.

     */

    public void deleteObserver(Observer observer) {

        deleteObserverReferenced(observer);

    }

    public void deleteObserver(Reference ref) {

        synchronized (obs) {

            obs.remove(ref);

        }

        deleteObserverReferenced((Observer) ref.get());

    }

    /**

     * If this object has changed, as indicated by the <code>hasChanged</code>

     * method, then notify all of its observers and then call the

     * <code>clearChanged</code> method to indicate that this object has no

     * longer changed.

     * <p>

     * Each observer has its <code>update</code> method called with two

     * arguments: this observable object and <code>null</code>. In other words,

     * this method is equivalent to: <blockquote><tt>

     * notifyObservers(null)</tt>

     * </blockquote>

     *

     * @see java.util.Observable#clearChanged()

     * @see java.util.Observable#hasChanged()

     * @see java.util.Observer#update(java.util.Observable, java.lang.Object)

     */

    public void notifyObservers() {

        notifyObservers(null);

    }

    /**

     * If this object has changed, as indicated by the <code>hasChanged</code>

     * method, then notify all of its observers and then call the

     * <code>clearChanged</code> method to indicate that this object has no

     * longer changed.

     * <p>

     * Each observer has its <code>update</code> method called with two

     * arguments: this observable object and the <code>arg</code> argument.                                        public void visit(Object obj)

                                                        throws VisitCanceledException, BaseException {

                                                // TODO Auto-generated method stub

                                        }

     *

     * @param arg

     *            any object.

     * @see java.util.Observable#clearChanged()

     * @see java.util.Observable#hasChanged()

     * @see java.util.Observer#update(java.util.Observable, java.lang.Object)

     */

    public void notifyObservers(Object arg) {

        if (!inComplex()) {

            setChanged();

            notify(this, arg);

        } else {

            complexNotification.addNotification(arg);

        }

    }

    /**

     * Clears the observer list so that this object no longer has any observers.

     */

    public void deleteObservers() {

        synchronized (obs) {

            obs.clear();

        }

    }

    /**

     * Returns the number of observers of this object.

     *

     * @return the number of observers of this object.

     */

    public int countObservers() {

        clearDeadReferences();

        synchronized (obs) {

            return obs.size();

        }

    }

    public void enableNotifications() {

        clearDeadReferences();

        propageNotifications = true;

    }

    public void disableNotifications() {

        propageNotifications = false;

    }

    public boolean isEnabledNotifications() {

        return propageNotifications;

    }

    public boolean inComplex() {

                return inComplexCount > 0;

    }

    public void beginComplexNotification() {

                if (inComplexCount == 0) {

                        clearDeadReferences();

                        clearChanged();

                        complexNotification = new DefaultComplexNotification();

                }

                inComplexCount++;

    }

    public void endComplexNotification() {

                if (inComplexCount > 0) {

                        if (inComplexCount == 1) {

                setChanged();

                notify(this, complexNotification);

                                complexNotification = null;

                        }

                        inComplexCount--;

                }

    }

        public Object clone() throws CloneNotSupportedException {

                BaseWeakReferencingObservable clone =

                                (BaseWeakReferencingObservable) super.clone();

                // Clone observers list

                if (countObservers() > 0) {

                        clone.setObservers(getObservers());

                }

                return clone;

        }

        private void setObservers(List observers) {

                this.obs = new ArrayList(observers);

        }

        private List getObservers() {

                return obs;

        }

    protected void notify(final WeakReferencingObservable observable,

        final Object notification) {

        if (!isEnabledNotifications()) {

            return;

        }

        /*

         * a temporary array buffer, used as a snapshot of the state of current

         * Observers.

         */

        Object[] arrLocal;

        synchronized (obs) {

            /*

             * We don't want the Observer doing callbacks into arbitrary code

             * while holding its own Monitor. The code where we extract each

             * DefaultObservable from the Vector and store the state of the

             * Observer needs synchronization, but notifying observers does not

             * (should not). The worst result of any potential race-condition

             * here is that: 1) a newly-added Observer will miss a notification

             * in progress 2) a recently unregistered Observer will be wrongly

             * notified when it doesn't care

             */

            if (!changed) {

                return;

            }

            arrLocal = obs.toArray();

            clearChanged();

        }

        // Go through all the registered observers and call update on them.

        // If any of the Reference is null, remove it from the list.

        for (int i = arrLocal.length - 1; i >= 0; i--) {

            final Observer observer =

                (Observer) ((Reference) arrLocal[i]).get();

            if (observer == null) {

                obs.remove(arrLocal[i]);

            } else {

                //If there is an error updating an observer, the exception 

                //has to be catched and next observer has to be updated. 

                //This exception is written in the log but would be fine to send 

                //a message to the user

                try{

                    // If the notification is complex, complex observers

                    // are able to handle it.

                    if (notification instanceof DefaultComplexNotification

                        && !(observer instanceof ComplexObserver)) {

                        ((DefaultComplexNotification) notification).accept(new Visitor() {

                            public void visit(Object simpleNotification) {

                                setChanged();

                                observer.update(observable, simpleNotification);

                            }

                        });

                    } else {

                        observer.update(observable, notification);

                    }

                }catch (Exception e){

                    LOG.error("Error notifying the observer", e);

                }

            }

        }

    }

    /**

     * Tests if this object has changed.

     *

     * @return <code>true</code> if and only if the <code>setChanged</code>

     *         method has been called more recently than the

     *         <code>clearChanged</code> method on this object;

     *         <code>false</code> otherwise.

     * @see java.util.Observable#clearChanged()

     * @see java.util.Observable#setChanged()

     */

    protected boolean hasChanged() {

        return changed;

    }

    /**

     * Marks this <tt>DefaultObservable</tt> object as having been changed; the

     * <tt>hasChanged</tt> method will now return <tt>true</tt>.

     */

    protected void setChanged() {

        changed = true;

    }

    /**

     * Indicates that this object has no longer changed, or that it has already

     * notified all of its observers of its most recent change, so that the

     * <tt>hasChanged</tt> method will now return <tt>false</tt>. This method is

     * called automatically by the <code>notifyObservers</code> methods.

     *

     * @see java.util.Observable#notifyObservers()

     * @see java.util.Observable#notifyObservers(java.lang.Object)

     */

    protected void clearChanged() {

        changed = false;

    }

    private void clearDeadReferences() {

        synchronized (obs) {

            Iterator iter = obs.iterator();

            while (iter.hasNext()) {

                Object obj = iter.next();

                if (obj instanceof Reference && ((Reference) obj).get() == null) {

                    iter.remove();

                }

            }

        }

    }

    private boolean contains(Observer observer) {

        synchronized (obs) {

            Iterator iter = obs.iterator();

            while (iter.hasNext()) {

                Object obj = iter.next();

                if (obj instanceof Reference) {

                    Object value = ((Reference) obj).get();

                    if (observer.equals(value)) {

                        return true;

                    }

                }

            }

        }

        return false;

    }

    private void deleteObserverReferenced(Observer observer) {

        if (observer == null) {

            return;

        }

        synchronized (obs) {

            Iterator iter = obs.iterator();

            while (iter.hasNext()) {

                Object obj = iter.next();

                if (obj instanceof Reference) {

                    Object value = ((Reference) obj).get();

                    if (value == null || observer.equals(value)) {

                        iter.remove();

                    }

                }

            }

        }

    }

}