Obtain the number of written bytes from BufferedOutputStream

Question

I am wondering if BufferedOutputStream offers any way to provide the count of bytes it has written. I am porting code from C# to Java. The code uses Stream.Position to obtain the count of written bytes.

Could anyone shed some light on this? This is not a huge deal because I can easily add a few lines of code to track the count. It would be nice if BufferedOutputStream already has the function.

Answer 1

For text there is a LineNumberReader, but no counting the progress of an OutputStream. You can add that with a wrapper class, a FilterOutputStream.

public class CountingOutputStream extends FilterOutputStream {
    
    private long count;
    private int bufferCount;
    
    public CountingOutputStream(OutputStream out) {
        super(out);
    }
    
    public long written() {
        return count;
    }
    
    public long willBeWritten() {
        return count + bufferCount;
    }
    
    @Override
    public void flush() {
        count += bufferCount;
        bufferCount = 0;
        super.flush();
    }

    public void write​(int b)
           throws IOException {
        ++bufferCount;
        super.write(b);     
    }
    @Override
    public void write(byte[] b, int off, int len)
           throws IOException {
        bufferCount += len;
        super.write(b, off, len);
    }
    
    @Override
    public void write(byte[] b, int off, int len)
           throws IOException {
        bufferCount += len;
        super.write(b, off, len);
    }
}

One could also think using a MemoryMappedByteBuffer (a memory mapped file) for a better speed/memory behavior. Created from a RandomAccessFile or FileChannel.

If all is too circumstantial, use the Files class which has many utilities, like copy. It uses Path - a generalisation of (disk I/O) File -, for files from the internet, files inside zip files, class path resources and so on.