code: @Override
      public void init(FilterConfig filterConfig) throws ServletException {
          try {
              expiration = Long.valueOf(filterConfig.getInitParameter(CacheConfigParameter.EXPIRATION.getName()));
          } catch (NumberFormatException e) {
              throw new ServletException(new StringBuilder("The initialization parameter ")
                      .append(CacheConfigParameter.EXPIRATION.getName())
                      .append(" is invalid or is missing for the filter ").append(filterConfig.getFilterName())
                      .append(".").toString());
          }
          cacheability = Boolean.valueOf(filterConfig.getInitParameter(CacheConfigParameter.PRIVATE.getName())) ? Cacheability.PRIVATE
                  : Cacheability.PUBLIC;
          mustRevalidate = Boolean.valueOf(filterConfig.getInitParameter(CacheConfigParameter.MUST_REVALIDATE.getName()));
          vary = filterConfig.getInitParameter(CacheConfigParameter.VARY.getName());
      }
docs: {@inheritDoc}