WatchingInputStream: Progress-reporting InputStream wrapper

WatchingInputStream.java

/**
 * WatchingInputStream: Progress-reporting InputStream wrapper.
 * This file is in public domain.
 */
public class WatchingInputStream extends FilterInputStream
{
    public interface ProgressListener
    {
        void onAdvance(long at, long length);
    }

    private int marked = 0;
    private long position = 0;
    private ProgressListener listener;

    public WatchingInputStream(InputStream in, ProgressListener listener)
    {
        super(in);
        this.listener = listener;
    }

    @Override
    public int read(byte[] buffer, int offset, int count) throws IOException
    {
        int advanced = super.read(buffer, offset, count);
        this.position += advanced;
        this.report();
        return advanced;
    }

    @Override
    public synchronized void reset() throws IOException
    {
        super.reset();
        this.position = this.marked;
    }

    @Override
    public synchronized void mark(int readlimit)
    {
        super.mark(readlimit);
        this.marked = readlimit;
    }

    @Override
    public long skip(long byteCount) throws IOException
    {
        long advanced = super.skip(byteCount);
        this.position += advanced;
        this.report();
        return advanced;
    }

    private void report()
    {
        if (this.listener == null)
            return;

        try
        {
            this.listener.onAdvance(this.position, this.position + this.in.available());
        }
        catch (IOException e)
        {
            this.listener.onAdvance(this.position, 0);
        }
    }
}