code: @Override
      public ServletContext getServletContext() {
          FilterConfig sc = getFilterConfig();
          if (sc == null) {
              throw new IllegalStateException(
                  lStrings.getString("err.filter_config_not_initialized"));
          }
  
          return sc.getServletContext();
      }
docs: <p>Returns a reference to the {@link ServletContext} in which this filter
  is running.  See {@link FilterConfig#getServletContext}.</p>
  
  <p>This method is supplied for convenience. It gets the
  context from the filter's <code>FilterConfig</code> object.
  
  @return ServletContext 	the <code>ServletContext</code> object
  passed to this filter by the <code>init</code>
  method
  
  @since Servlet 4.0