code: private Date getLastModifiedTime(URL url) {
  
  		// see http://stackoverflow.com/questions/2416872/how-do-you-obtain-modified-date-from-a-remote-file-java
  		Date date = null;
  		try {
  			String lastModified = url.openConnection().getHeaderField("Last-Modified");
  			logger.debug("Last modified date of server file ({}) is {}",url.toString(),lastModified);
  
  
  			if (lastModified!=null) {
  
  				try {
  					date = new SimpleDateFormat("E, d MMM yyyy HH:mm:ss Z", Locale.ENGLISH).parse(lastModified);
  				} catch (ParseException e) {
  					logger.warn("Could not parse last modified time from string '{}', no last modified time available for file {}",
  							lastModified, url.toString());
  					// this will return null
  				}
  
  			}
  		} catch (IOException e) {
  			logger.warn("Problems while retrieving last modified time for file {}", url.toString());
  		}
  		return date;
  
  	}
docs: Get the last modified time of the file in given url by retrieveing the "Last-Modified" header.
  Note that this only works for http URLs
  @param url
  @return the last modified date or null if it couldn't be retrieved (in that case a warning will be logged)