BackwardsFileInputStream.java

package com.idega.util;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;

/**
 * <p>
 * Class to read a text file backwards. Can be used to read a "tail" of a text file.
 * </p>
 *  Last modified: $Date: 2007/07/23 08:18:21 $ by $Author: civilis $
 * 
 * @author <a href="mailto:tryggvil@idega.com">tryggvil</a>
 * @version $Revision: 1.2 $
 */
public class BackwardsFileInputStream extends InputStream
{
    public BackwardsFileInputStream(File file) throws IOException
    {
        //assert (file != null) && file.exists() && file.isFile() && file.canRead();
        
        raf = new RandomAccessFile(file, "r");
        currentPositionInFile = raf.length();
        currentPositionInBuffer = 0;
    }
    
    public int read() throws IOException
    {
        if (currentPositionInFile <= 0)
            return -1;
        if (--currentPositionInBuffer < 0)
        {
            currentPositionInBuffer = buffer.length;
            long startOfBlock = currentPositionInFile - buffer.length;
            if (startOfBlock < 0)
            {
                currentPositionInBuffer = buffer.length + (int)startOfBlock;
                startOfBlock = 0;
            }
            raf.seek(startOfBlock);
            raf.readFully(buffer, 0, currentPositionInBuffer);
            return read();
        }
        currentPositionInFile--;
        return buffer[currentPositionInBuffer];
    }
    
    public void close() throws IOException
    {
        raf.close();
    }
    
    private final byte[] buffer = new byte[4096];
    private final RandomAccessFile raf;
    private long currentPositionInFile;
    private int currentPositionInBuffer;
}