Uploading file: Progress Listener

When uploading bytes, an application might need to take some action depending on where the upload status is.

The AsyncHttpClient library support a special AsyncHandler called ProgressAsyncHandler that can be used to track the upload operation:

public interface ProgressAsyncHandler<T> extends AsyncHandler<T> {
    STATE onHeaderWriteCompleted();
    STATE onContentWriteCompleted();
    STATE onContentWriteProgress(long amount, long current, long total);
}

The methods are called in the following order:

• onHeaderWriteCompleted: invoked when the headers has been flushed to the remote server
• onContentWriteProgress: as soon as some response's body bytes are written. Might be invoked many times.
• onContentWriteCompleted: invoked when the response has been sent or aborted.

  Like with AsyncHandler, you can always always abort the processing at any moment in the upload process.