public void setFilterConfig(FilterConfig filterConfig) {
        this.filterConfig = filterConfig;
        setServletContext(filterConfig.getServletContext());
    }
Sets the FilterConfig <em>and</em> the {@code ServletContext} as attributes of this class for use by
subclasses.  That is:
<pre>
this.filterConfig = filterConfig;
setServletContext(filterConfig.getServletContext());</pre>

@param filterConfig the FilterConfig instance provided by the Servlet container at start-up.
web/src/main/java/org/apache/shiro/web/servlet/AbstractFilter.java