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A remote dynamic Command pattern with GWT and LinkSet

, 19 Jan 2011
Command pattern is a very useful solution, but it causes some problems when used in a distributed environment.
// -----------------------------------------------------------------------------
//    LinkSet
//    Copyright: 2010 Lukasz Bownik (lukasz.bownik@gmail.com)
//
//    This file is part of LinkSet.
//
//    LinkSet is free software; you can redistribute it and/or modify
//    it under the terms of the Lesser GNU General Public License as published by
//    the Free Software Foundation; either version 2 of the License, or
//    (at your option) any later version.
//
//    LinkSet 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
//    Lesser GNU General Public License for more details.
//
//    You should have received a copy of the Lesser GNU General Public License
//    along with LinkSet; if not, write to the Free Software
//    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
// -----------------------------------------------------------------------------
package org.linkset;

import java.lang.reflect.InvocationTargetException;
import java.util.ArrayList;

/*******************************************************************************
 * The class that handles listener collections.
 * 
 * @author Lukasz Bownik (lukasz.bownik@gmail.com)
 ******************************************************************************/
public final class DefaultListenerManager implements ListenerManager {

	/***************************************************************************
	 * A default constructor. This construcotr is equivalnet to
	 * DefaultListenerManager(null)
	 * 
	 * @see DefaultListenerManager#DefaultListenerManager(java.lang.Class<?>[])
	 **************************************************************************/
	public DefaultListenerManager() {

		this((Class<?>[]) null);
	}

	/***************************************************************************
	 * A construtor
	 * 
	 * @param parameterTypes
	 *            the array of parameter types of event handler methods, if null
	 *            then the parameter types are not checked for consistency
	 **************************************************************************/
	public DefaultListenerManager(final Class<?>... parameterTypes) {

		this.parameterTypes = parameterTypes;
	}

	/***************************************************************************
	 * @see ListenerManager#add(java.lang.Object, java.lang.String)
	 **************************************************************************/
	public void add(final Object target, final String methodId) {

		final MethodPointer pointer = new MethodPointer(target, methodId);
		if (!this.pointers.contains(pointer)) {

			if (this.parameterTypes != null) {
				pointer.ensureParameterTypes(this.parameterTypes);
			}
			this.pointers.add(pointer);
		}
	}

	/***************************************************************************
	 * @see ListenerManager#remove(java.lang.Object, java.lang.String)
	 **************************************************************************/
	public void remove(final Object target, final String methodId) {

		this.pointers.remove(new MethodPointer(target, methodId));
	}

	/***************************************************************************
	 * @see ListenerManager#removeAll(java.lang.Object)
	 **************************************************************************/
	public void removeAll(final Object target) {

		if (target == null) {
			throw new NullPointerException("Null target.");
		}

		int index = 0;
		while (index < this.pointers.size()) {
			if (this.pointers.get(index).target == target) {
				this.pointers.remove(index);
			} else {
				++index;
			}
		}
	}

	/***************************************************************************
	 * @return true if a set is empty
	 **************************************************************************/
	public boolean isEmpty() {

		return this.pointers.isEmpty();
	}

	/***************************************************************************
	 * @return the amount of listeners in this set
	 **************************************************************************/
	public int size() {

		return this.pointers.size();
	}

	/***************************************************************************
	 * Clears the set
	 **************************************************************************/
	public void clear() {

		this.pointers.clear();
	}

	/***************************************************************************
	 * Invokes all the listeners in this set. The order of invocation is not
	 * specified. Throws an exception if something goes wrong. Invocation of all
	 * listeners is not guaranteed if an axception is thrown.
	 * 
	 * @param args
	 *            method arguments or null for no argument listeners
	 * @throws ExceptionInInitializerError
	 *             if the initialization provoked by any method fails.
	 * @throws InvocationTargetException
	 *             if any underlying method throws an exception.
	 **************************************************************************/
	public void invokeAll(final Object... args)
			throws InvocationTargetException, ExceptionInInitializerError {

		for (final MethodPointer pointer : this.pointers) {
			pointer.invoke(args);
		}
	}

	/***************************************************************************
	 * This method is equivalent to invokeAll(null)
	 * 
	 * @see ListenerManager#invokeAll(java.lang.Object[])
	 **************************************************************************/
	public void invokeAll() throws InvocationTargetException,
			ExceptionInInitializerError {

		invokeAll((Object[]) null);
	}

	/***************************************************************************
     *
     **************************************************************************/
	private final ArrayList<MethodPointer> pointers = new ArrayList<MethodPointer>();
	private final Class<?>[] parameterTypes;
}

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This article, along with any associated source code and files, is licensed under The GNU Lesser General Public License (LGPLv3)

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