How does one display progress of a file copy operation in Java. without using Swing e.g. in a Web app?

Question

I have a web application which needs to perform a file copy operation and show user a progress bar.

Currently, the copy is being done by calling cpio which

Answer 1

Basically, you should use a listener pattern. In this example the listener has a single method to accept the # of bytes which were just written. It could be pre-populated with the total file size to calculate a percentage to show on the screen.

ReadableByteChannel source = ...;
WritableByteChannel dest = ...;
FileCopyListener listener = ...;


ByteBuffer buf = ByteBuffer.allocateDirect(BUFFER_SIZE);
while (src.read(buf) != -1) {
  buf.flip();
  int writeCount = dest.write(buf);
  listener.bytesWritten(writeCount);
  buf.compact();
}
buf.flip();
while (buffer.hasRemaining()) {
  int writeCount = dest.write(buf);
  listener.bytesWritten(writeCount);
}