stringfixedlength.java

java+eclipse做的TTPlayer

/**
 *  @author : Paul Taylor
 *  @author : Eric Farng
 *
 *  Version @version:$Id: StringFixedLength.java,v 1.11 2007/08/07 14:36:15 paultaylor Exp $
 *
 *  MusicTag Copyright (C)2003,2004
 *
 *  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,
 *  you can get a copy from http://www.opensource.org/licenses/lgpl-license.php or write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
 * Description:
 *
 */
package com.hadeslee.audiotag.tag.datatype;

import com.hadeslee.audiotag.tag.id3.AbstractTagFrameBody;
import com.hadeslee.audiotag.tag.InvalidDataTypeException;
import com.hadeslee.audiotag.tag.id3.valuepair.TextEncoding;

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.*;


/**
 * Represents a fixed length String, whereby the length of the String is known. The String
 * will be encoded based upon the text encoding of the frame that it belongs to.
 */
public class StringFixedLength
    extends AbstractString
{
    /**
     * Creates a new ObjectStringFixedsize datatype.
     *
     * @param identifier 
     * @param size       
     * @throws IllegalArgumentException 
     */
    public StringFixedLength(String identifier, AbstractTagFrameBody frameBody, int size)
    {
        super(identifier, frameBody);
        if (size < 0)
        {
            throw new IllegalArgumentException("size is less than zero: " + size);
        }
        setSize(size);
    }

    public StringFixedLength(StringFixedLength copyObject)
    {
        super(copyObject);
        this.size = copyObject.size;
    }

    /**
     * 
     *
     * @param obj 
     * @return if obj is equivalent to this
     */
    public boolean equals(Object obj)
    {
        if ((obj instanceof StringFixedLength) == false)
        {
            return false;
        }
        StringFixedLength object = (StringFixedLength) obj;
        if (this.size != object.size)
        {
            return false;
        }
        return super.equals(obj);
    }

    /**
     * Read a string from buffer of fixed size(size has already been set in constructor)
     *
     * @param arr    this is the buffer for the frame
     * @param offset this is where to start reading in the buffer for this field
     */
    public void readByteArray(byte[] arr, int offset) throws InvalidDataTypeException
    {
        logger.info("Reading from array from offset:" + offset);
        try
        {
            String charSetName = getTextEncodingCharSet();
            CharsetDecoder decoder = Charset.forName(charSetName).newDecoder();

            //Decode buffer if runs into problems should through exception which we
            //catch and then set value to empty string.
            logger.finest("Array length is:" + arr.length + "offset is:" + offset + "Size is:" + size);


            if(arr.length - offset < size)
            {
                throw new InvalidDataTypeException("byte array is to small to retrieve string of declared length:"+size);
            }
            String str = decoder.decode(ByteBuffer.wrap(arr, offset, size)).toString();
            if (str == null)
            {
                throw new NullPointerException("String is null");
            }
            value = str;
        }
        catch (CharacterCodingException ce)
        {
            logger.severe(ce.getMessage());
            value = "";
        }
        logger.info("Read StringFixedLength:" + value);
    }

    /**
     * Write String into byte array
     *
     * The string will be adjusted to ensure the correct number of bytes are written, If the current value is null
     * or to short the written value will have the 'space' character appended to ensure this. We write this instead of
     * the null character because the null character is likely to confuse the parser into misreading the next field.
     *
     * @return the byte array to be written to the file
     */
    public byte[] writeByteArray()
    {
        ByteBuffer dataBuffer = null;
        byte[] data;

        //Create with a series of empty of spaces to try and ensure integrity of field
        if(value==null)
        {
            logger.warning("Value of StringFixedlength Field is null using default value instead");
            data = new byte[size];
            for(int i=0;i<size;i++)
            {
                data[i]=' ';
            }
            return data;
        }

        try
        {
            String charSetName = getTextEncodingCharSet();
            CharsetEncoder encoder = Charset.forName(charSetName).newEncoder();
            dataBuffer = encoder.encode(CharBuffer.wrap((String) value));
        }
        catch (CharacterCodingException ce)
        {
            logger.warning("There was a problem writing the following StringFixedlength Field:"+value+":"+ce.getMessage()+"using default value instead");
            data = new byte[size];
            for(int i=0;i<size;i++)
            {
                data[i]=' ';
            }
            return data;
        }

        // We must return the defined size.
        // To check now because size is in bytes not chars
        if (dataBuffer != null)
        {
            //Everything ok
            if (dataBuffer.limit() == size)
            {
                data = new byte[dataBuffer.limit()];
                dataBuffer.get(data, 0, dataBuffer.limit());
                return data;
            }
            //There is more data available than allowed for this field strip
            else if (dataBuffer.limit() > size)
            {
                logger.warning("There was a problem writing the following StringFixedlength Field:"
                    +value
                    +" when converted to bytes has length of:"+dataBuffer.limit()
                    +" but field was defined with length of:"+size
                    +" too long so stripping extra length");
                data = new byte[size];
                dataBuffer.get(data, 0, size);
                return data;
            }
            //There is not enough data
            else
            {
                logger.warning("There was a problem writing the following StringFixedlength Field:"
                    +value
                    +" when converted to bytes has length of:"+dataBuffer.limit()
                    +" but field was defined with length of:"+size
                    +" too short so padding with spaces to make up extra length");

                data = new byte[size];
                dataBuffer.get(data, 0, dataBuffer.limit());

                for(int i=dataBuffer.limit();i<size;i++)
                {
                    data[i]=' ';
                }
                return data;
            }
        }
        else
        {
            logger.warning("There was a serious problem writing the following StringFixedlength Field:"+value+":"+"using default value instead");
            data = new byte[size];
            for(int i=0;i<size;i++)
            {
                data[i]=' ';
            }
            return data;
        }
    }

    /**
     *
     * @return the encoding of the frame body this datatype belongs to
     */
    protected String  getTextEncodingCharSet()
    {
         byte textEncoding = this.getBody().getTextEncoding();
         String charSetName = TextEncoding.getInstanceOf().getValueForId(textEncoding);
         logger.finest("text encoding:"+textEncoding + " charset:"+charSetName);
         return charSetName;
    }
}