encodings.java

java处理声音文件

/*
 *	Encodings.java
 */

/*
 *  Copyright (c) 2000 by Florian Bomers <[e-mail]>
 *
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Library 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 Library General Public License for more details.
 *
 *   You should have received a copy of the GNU Library General Public
 *   License along with this program; if not, write to the Free Software
 *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 */


package	org.tritonus.sampled;

import	java.util.Iterator;
import	javax.sound.sampled.AudioSystem;
import	javax.sound.sampled.AudioFormat;
import	org.tritonus.util.StringHashedSet;
import	org.tritonus.TDebug;

/**
 * This class is a proposal for generic handling of encodings.
 * The main purpose is to provide a standardized way of
 * implementing encoding types. Like this, encodings
 * are only identified by their String name, and not, as currently,
 * by their object instance.
 * <p>
 * A registry of standard encoding names will
 * be maintained by the Tritonus team.
 * <p>
 * In a specification request to JavaSoft, the static method
 * <code>getEncoding</code> should be integrated into 
 * <code>AudioFormat.Encoding(String name)</code> (possibly 
 * renamed to <code>getInstance(String name)</code>.<br>
 * The static instances of ULAW, ALAW PCM_UNSIGNED and PCM_SIGNED
 * encodings in that class should be retrieved using that function, 
 * too (internally).<br>
 * At best, the protected constructor of that class
 * should also be replaced to be a private constructor.
 * Like this it will be prevented that developers create their own
 * instances of Encoding, which causes problems with the
 * equals method. In fact, the equals method should be redefined anyway
 * so that it compares the names and not the objects.
 * <p>
 * Also, a specification request should be made to integrate
 * <code>getEncodings()</code> into AudioSystem (this is
 * especially annoying as the relevant methods already exist
 * in the provider interfaces of file readers, file writers and 
 * converters).
 *
 * @author Florian Bomers
 */
public class Encodings extends AudioFormat.Encoding {

	/** contains all known encodings */
	private static StringHashedSet encodings = new StringHashedSet();

	// initially add the standard encodings
	static {
		encodings.add(AudioFormat.Encoding.PCM_SIGNED);
		encodings.add(AudioFormat.Encoding.PCM_UNSIGNED);
		encodings.add(AudioFormat.Encoding.ULAW);
		encodings.add(AudioFormat.Encoding.ALAW);
	}

	Encodings(String name) {
		super(name);
	}

	/**
	 * Use this method for retrieving an instance of
	 * <code>AudioFormat.Encoding</code> of the specified
	 * name. A standard registry of encoding names will
	 * be maintained by the Tritonus team.
	 * <p>
	 * Every file reader, file writer, and format converter
	 * provider should exclusively use this method for
	 * retrieving instances of <code>AudioFormat.Encoding</code>.
	 */
	public static AudioFormat.Encoding getEncoding(String name) {
		AudioFormat.Encoding res=(AudioFormat.Encoding) encodings.get(name);
		if (res==null) {
			// it is not already in the string set. Create a new encoding instance.
			res=new Encodings(name);
			// and save it for the future
			encodings.add(res);
		}
		return res;
	}

	/**
	 * Returns all &quot;supported&quot; encodings. 
	 * Supported means that it is possible to read or
	 * write files with this encoding, or that a converter
	 * accepts this encoding as source or target format.
	 * <p>
	 * Currently, this method returns a best guess and
	 * the search algorithm is far from complete: with standard
	 * methods of AudioSystem, only the target encodings
	 * of the converters can be retrieved - neither
	 * the source encodings of converters nor the encodings
	 * of file readers and file writers cannot be retrieved.
	 */
	public static AudioFormat.Encoding[] getEncodings() {
		StringHashedSet iteratedSources=new StringHashedSet();
		StringHashedSet retrievedTargets=new StringHashedSet();
		Iterator sourceFormats=encodings.iterator();
		while (sourceFormats.hasNext()) {
			AudioFormat.Encoding source=(AudioFormat.Encoding) sourceFormats.next();
			iterateEncodings(source, iteratedSources, retrievedTargets);
		}
		return (AudioFormat.Encoding[]) retrievedTargets.toArray(
		           new AudioFormat.Encoding[retrievedTargets.size()]);
	}


	private static void iterateEncodings(AudioFormat.Encoding source,
	                                     StringHashedSet iteratedSources,
	                                     StringHashedSet retrievedTargets) {
		if (!iteratedSources.contains(source)) {
			iteratedSources.add(source);
			AudioFormat.Encoding[] targets=AudioSystem.getTargetEncodings(source);
			for (int i=0; i<targets.length; i++) {
				AudioFormat.Encoding target=targets[i];
				if (retrievedTargets.add(target.toString())) {
					iterateEncodings(target, iteratedSources,retrievedTargets);
				}
			}
		}
	}
}



/*** Encodings.java ***/