id3v2extendedheader.java

java声音播放管理

/**
 * Copyright (C) 2001 Jonathan Hilliker
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
 * Description: 
 *  If the id3v2 tag has an extended header, this class will read/write the 
 *  information contained within it.  NOTE: this class is untested and has
 *  no mutators.  In other words, this class will only be used if an mp3
 *  already has an extended header (at this point at least).
 *
 * @author:  Jonathan Hilliker
 * @version: $Id: ID3v2ExtendedHeader.java,v 1.2 2001/10/19 03:57:53 helliker Exp $
 * Revsisions: 
 *  $Log: ID3v2ExtendedHeader.java,v $
 *  Revision 1.2  2001/10/19 03:57:53  helliker
 *  All set for release.
 *
 *
 */

package helliker.id3;

import java.io.*;

public class ID3v2ExtendedHeader {
    
    private final int EXT_HEAD_LOCATION = 10;
    private final int MIN_SIZE = 6;
    private final int CRC_SIZE = 5;
    private final int[] MAX_TAG_FRAMES_TABLE = { 128, 64, 32, 32 };
    private final int[] MAX_TAG_SIZE_TABLE = {8000000, 1024000, 320000, 32000};
    private final int[] MAX_TEXT_SIZE_TABLE = { -1, 1024, 128, 30 };

    private File mp3 = null;
    private int size;
    private int numFlagBytes;
    private boolean update;
    private boolean crced;
    private byte[] crc;
    private int maxFrames;
    private int maxTagSize;
    private boolean textEncode;
    private int maxTextSize;
    private boolean imageEncode;
    private int imageRestrict;

    /**
     * Create an extended header object from the file passed.  Information
     * in the file's extended header will be read and stored.
     *
     * @param mp3 the file to read/write to
     * @exception FileNotFoundException if an error occurs
     * @exception IOException if an error occurs
     * @exception ID3v2FormatException if an error occurs
     */
    public ID3v2ExtendedHeader( File mp3 ) 
	throws FileNotFoundException, IOException, ID3v2FormatException {

	this.mp3 = mp3;

	size = 0;
	numFlagBytes = 0;
	update = false;
	crced = false;
	crc = new byte[CRC_SIZE];
	maxFrames = -1;
	maxTagSize = -1;
	textEncode = false;
	maxTextSize = -1;
	imageEncode = false;
	imageRestrict = -1;

	readExtendedHeader();
    }

    /**
     * Read the information in the file's extended header
     *
     * @exception FileNotFoundException if an error occurs
     * @exception IOException if an error occurs
     * @exception ID3v2FormatException if an error occurs
     */
    private void readExtendedHeader() 
	throws FileNotFoundException, IOException, ID3v2FormatException {

	RandomAccessFile raf = new RandomAccessFile( mp3, "r" );
	raf.seek( EXT_HEAD_LOCATION );

	byte[] buf = new byte[4];
	if( raf.read( buf ) != buf.length ) {
	    throw new IOException("Error reading extended header:size");
	}

	size = BinaryParser.convertToInt( buf );
	if( size < MIN_SIZE ) {
	    throw new ID3v2FormatException( "The extended header size data" +
				" is less than the minimum required size.");
	}

	buf = new byte[1];
	if( raf.read( buf ) != buf.length ) {
	    throw new IOException("Error reading extended header:numflags");
	}

	numFlagBytes = (int)buf[0];
	buf = new byte[numFlagBytes+1];

	if( raf.read( buf ) != buf.length ) {
	    throw new IOException( "Error reading extended header:flags" );
	}

	parseFlags( buf );

	raf.close();
    }

    /**
     * Parse the extended header flag bytes
     *
     * @param flags the array of extended flags
     * @exception ID3v2FormatException if an error occurs
     */
    private void parseFlags( byte[] flags ) throws ID3v2FormatException {
	int bytesRead = 1;

	if( BinaryParser.bitSet( flags[0], 6 ) ) {
	    update = true;
	    bytesRead += 1;
	}
	if( BinaryParser.bitSet( flags[0], 5 ) ) {
	    crced = true;
	    bytesRead += 1;
	    for( int i = 0; i < crc.length; i++ ) {
		crc[i] = flags[bytesRead++];
	    }
	}
	if( BinaryParser.bitSet( flags[0], 4 ) ) {
	    bytesRead += 1;
	    maxTagSize = BinaryParser.convertToDecimal( 
						flags[bytesRead], 6, 7 );
	    textEncode = BinaryParser.bitSet( flags[bytesRead], 5 );
	    maxTextSize = BinaryParser.convertToDecimal( 
						flags[bytesRead], 3, 4 );
	    imageEncode = BinaryParser.bitSet( flags[bytesRead], 2 );
	    imageRestrict = BinaryParser.convertToDecimal( 
						flags[bytesRead], 0, 1 );
	    bytesRead += 1;
	}

	if( bytesRead != numFlagBytes ) {
	    throw new ID3v2FormatException("The number of found flag bytes " +
					   "in the extended header is not " +
					   "equal to the number specified " +
					   "in the extended header." );
	}
    }

    /**
     * Return an array of bytes representing this extended header in the 
     * standard format to be written to a file.
     *
     * @return a binary represenation of this extended header
     */
    public byte[] getBytes() {
	byte[] b = new byte[size];
	int bytesCopied = 0;

	System.arraycopy( BinaryParser.convertToBytes(size), 0, b, 
			  bytesCopied, 4 );
	bytesCopied += 4;
	b[bytesCopied++] = (byte)numFlagBytes;
	System.arraycopy( getFlagBytes(), 0, b, bytesCopied, numFlagBytes );
	bytesCopied += numFlagBytes;

	return b;
    }

    /**
     * A helper function for the getBytes method that returns a byte array
     * representing the extended flags field of the extended header.
     *
     * @return the extended flags field of the extended header
     */
    private byte[] getFlagBytes() {
	byte[] b = new byte[numFlagBytes];
	int bytesCopied = 1;
	b[0] = 0;

	if( update ) {
	    b[0] = BinaryParser.setBit( b[0], 7 );
	    b[bytesCopied++] = 0;
	}
	if( crced ) {
	    b[0] = BinaryParser.setBit( b[0], 6 );
	    b[bytesCopied++] = (byte)crc.length;
	    System.arraycopy( crc, 0, b, bytesCopied, crc.length );
	    bytesCopied += crc.length;
	}
	if( (maxTagSize != -1) || textEncode || (maxTextSize != -1) || 
	    imageEncode || (imageRestrict != -1) ) {
	    
	    b[0] = BinaryParser.setBit( b[0], 5 );
	    b[bytesCopied++] = 0x01;
	    byte restrict = 0;
	    if( maxTagSize != -1 ) {
		if( BinaryParser.bitSet( (byte)maxTagSize, 0 ) ) {
		    restrict = BinaryParser.setBit( restrict, 6 );
		}
		if( BinaryParser.bitSet( (byte)maxTagSize, 1 ) ) {
		    restrict = BinaryParser.setBit( restrict, 7 );
		}
	    }
	    if( textEncode ) {
		restrict = BinaryParser.setBit( restrict, 5 );
	    }
	    if( maxTextSize != -1 ) {
		if( BinaryParser.bitSet( (byte)maxTextSize, 0 ) ) {
		    restrict = BinaryParser.setBit( restrict, 3 );
		}
		if( BinaryParser.bitSet( (byte)maxTextSize, 1 ) ) {
		    restrict = BinaryParser.setBit( restrict, 4 );
		}
	    }
	    if( imageEncode ) {
		restrict = BinaryParser.setBit( restrict, 2 );
	    }
	    if( imageRestrict != -1 ) {
		if( BinaryParser.bitSet( (byte)imageRestrict, 0 ) ) {
		    restrict = BinaryParser.setBit( restrict, 0 );
		}
		if( BinaryParser.bitSet( (byte)imageRestrict, 1 ) ) {
		    restrict = BinaryParser.setBit( restrict, 1 );
		}
	    }

	    b[bytesCopied++] = restrict;
	}


	return b;
    }

    /**
     * Returns the size of the extended header
     *
     * @return the size of the extended header
     */
    public int getSize() {
	return size;
    }

    /**
     * Returns the number of extended flag bytes
     *
     * @return the number of extended flag bytes
     */
    public int getNumFlagBytes() {
	return numFlagBytes;
    }

    /**
     * Returns the maximum number of frames if set.  If unset, returns -1
     *
     * @return the maximum number of frames or -1 if unset
     */
    public int getMaxFrames() {
	int retval = -1;

	if( (maxTagSize >= 0) && (maxTagSize < MAX_TAG_FRAMES_TABLE.length) ) {
	    retval = MAX_TAG_FRAMES_TABLE[maxTagSize];
	}

	return retval;
    }

    /**
     * Returns the maximum tag size or -1 if unset
     *
     * @return the maximum tag size or -1 if unset
     */
    public int getMaxTagSize() {
	int retval = -1;

	if( (maxTagSize >= 0) && (maxTagSize < MAX_TAG_SIZE_TABLE.length) ) {
	    retval = MAX_TAG_SIZE_TABLE[maxTagSize];
	}

	return retval;
    }

    /**
     * Returns true if the text encode flag is set
     *
     * @return true if the text encode flag is set
     */
    public boolean getTextEncode() {
	return textEncode;
    }

    /**
     * Returns the maximum length of a string if set or -1
     *
     * @return the maximum length of a string if set or -1
     */
    public int getMaxTextSize() {
	int retval = -1;

	if( (maxTextSize >= 0) && (maxTextSize < MAX_TEXT_SIZE_TABLE.length)) {
	    retval = MAX_TEXT_SIZE_TABLE[maxTextSize];
	}

	return retval;
    }

    /**
     * Returns true if the image encode flag is set
     *
     * @return true if the image encode flag is set
     */
    public boolean getImageEncode() {
	return imageEncode;
    }

    /**
     * Returns the value of the image restriction field or -1 if not set
     *
     * @return the value of the image restriction field or -1 if not set
     */
    public int getImageRestriction() {
	return imageRestrict;
    }

    /**
     * Returns true if this tag is an update of a previous tag
     *
     * @return true if this tag is an update of a previous tag
     */
    public boolean getUpdate() {
	return update;
    }

    /**
     * Returns true if CRC information is provided for this tag
     *
     * @return true if CRC information is provided for this tag
     */
    public boolean getCRCed() {
	return crced;
    }

    /**
     * If there is crc data in the extended header, then the attached 5 byte
     * crc will be returned.  An empty array will be returned if this has
     * not been set.
     *
     * @return the attached crc data if there is any
     */
    public byte[] getCRC() {
	return crc;
    }

    /**
     * Returns a string representation of this object that contains all
     * information within.
     *
     * @return a string representation of this object
     */
    public String toString() {
	return "ExtendedSize:\t\t\t" + getSize() + " bytes" + 
	    "\nNumFlagBytes:\t\t\t" + getNumFlagBytes() + 
	    "\nUpdated:\t\t\t" + getUpdate() + "\nCRC:\t\t\t\t" + getCRCed() +
	    "\nMaxFrames:\t\t\t" 
	    + getMaxFrames() + "\nMaxTagSize:\t\t\t" + getMaxTagSize() +
	    "\nTextEncoded:\t\t\t" + getTextEncode() + "\nMaxTextSize:\t\t\t"
	    + getMaxTextSize() + "\nImageEncoded:\t\t\t" + getImageEncode()
	    + "\nImageRestriction:\t\t" + getImageRestriction();
    }

} // ID3v2ExtendedHeader