public int copy(InputStream input,
    OutputStream output) throws IOException 
{
        byte[] buffer = new byte[getBufferSize()];
        int count = 0;
        int n = 0;
        while (-1 != (n = input.read(buffer))) {
            output.write(buffer, 0, n);
            count += n;
        }
        return count;
}

Copy bytes from an InputStream to an OutputStream.

 public ActionForward execute(ActionMapping mapping,
    ActionForm form,
    HttpServletRequest request,
    HttpServletResponse response) throws Exception 
{
        StreamInfo info = getStreamInfo(mapping, form, request, response);
        String contentType = info.getContentType();
        InputStream stream = info.getInputStream();
        try {
            response.setContentType(contentType);
            copy(stream, response.getOutputStream());
        } finally {
            if (stream != null) {
                stream.close();
            }
        }
        // Tell Struts that we are done with the response.
        return null;
}

Process the specified HTTP request, and create the corresponding HTTP response (or forward to another web component that will create it). Return an ActionForward instance describing where and how control should be forwarded, or null if the response has already been completed.

 protected int getBufferSize() 
{
                                                                                          
        return DEFAULT_BUFFER_SIZE;
}

Returns the size of the buffer to be used in transferring the data to the servlet output stream. This method may be overridden by an extending class in order to customize the buffer size.

 abstract protected DownloadAction.StreamInfo getStreamInfo(ActionMapping mapping,
    ActionForm form,
    HttpServletRequest request,
    HttpServletResponse response) throws Exception
Returns the information on the file, or other stream, to be downloaded
by this action. This method must be implemented by an extending class.