code: public static String getCRC32Checksum(InputStream is) throws IOException {
  
  		Checksum checksum = new CRC32();
  
  		byte[] bytes = new byte[1024];
  		int len = 0;
  
  		while ((len = is.read(bytes)) >= 0) {
  			checksum.update(bytes, 0, len);
  		}
  
  		return Long.toString(checksum.getValue());
  	}
docs: Returns the CRC 32 Checksum of the input stream
  
  @param is
  the input stream
  
  @return the CRC 32 checksum of the input stream
  @throws IOException
  if an IO exception occurs