code: public DbxEntry./*@Nullable*/File getFile(String path, /*@Nullable*/String rev, OutputStream target)
          throws DbxException, IOException
      {
          Downloader downloader = startGetFile(path, rev);
          if (downloader == null) return null;
          return downloader.copyBodyAndClose(target);
      }
docs: Retrieves a file's content and writes it to the given {@code OutputStream}.
  
  <pre>
  DbxClientV1 dbxClient = ...
  DbxEntry.File md;
  File target = new File("Copy of House.jpeg");
  OutputStream out = new FileOutputStream(target);
  try {
  md = dbxClient.getFile("/Photos/House.jpeg", out);
  }
  finally {
  out.close();
  }
  </pre>
  
  @param rev
  The {@link DbxEntry.File#rev rev} of the file to retrieve,
  or {@code null} if you want the latest revision of the file.
  
  @return
  The downloaded file's metadata, or {@code null}
  
  @throws IOException
  If there's an error writing to {@code target}.