private void handleRemoveFeedPost(Request request, HttpServletResponse httpServletResponse)
      throws Exception {
    LOG.info("removing feed");
    User user = userHelpers.getUser(request);

    try {
      if (user == null) {
        LOG.error("User not found");
        return;
      }

      String feedId = request.getParameter(PARAM_FEED_ID);

      LOG.info(String.format("Removing feed %s for user %s", feedId, user));

      // ttt1 add some validation; probably best try to actually get data, set the title, ...
      if (feedId == null || feedId.equals("")) {
        LOG.error("feed not specified");
        // ttt1 show some error
        return;
      }

      if (user.feedIds.remove(
          feedId)) { // ttt2 clean up the global feed table; that's probably better done if nobody
                     // accesses a feed for 3 months or so
        userDb.updateFeeds(user);
        LOG.info(String.format("Removed feed %s for user %s", feedId, user));
      } else {
        LOG.info(String.format("No feed found with ID %s for user %s", feedId, user));
      }
    } finally {
      httpServletResponse.sendRedirect(PATH_FEED_ADMIN);
    }
  }
  private void handleAddFeedPost(Request request, HttpServletResponse httpServletResponse)
      throws Exception {
    LOG.info("adding feed");
    User user = userHelpers.getUser(request);

    try {
      if (user == null) {
        LOG.error("User not found");
        return;
      }

      String url = request.getParameter(PARAM_NEW_FEED_URL);
      // ttt1 add some validation; probably best try to actually get data, set the title, ...
      if (url == null || url.equals("")) {
        LOG.error("New feed not specified");
        // ttt1 show some error
        return;
      }

      MessageDigest digest = MessageDigest.getInstance("MD5");
      String feedId = PrintUtils.byteArrayAsUrlString(digest.digest(url.getBytes("UTF-8")));
      feedId = feedId.substring(0, Config.getConfig().feedIdSize);

      Feed feed = feedDb.get(feedId);
      if (feed == null) {
        feed = new Feed(feedId, url);
        feedDb.add(feed);
      }

      if (user.feedIds.contains(feedId)) {
        LOG.error(String.format("Trying to add existing feed %s to user %s", feedId, user));
      } else {
        user.feedIds.add(feedId);
        userDb.updateFeeds(user);
      }
    } finally {
      httpServletResponse.sendRedirect(PATH_FEED_ADMIN);
    }
  }