protected boolean preHandle(ServletRequest request, ServletResponse response) throws Exception {
        return true;
    }
Returns {@code true} if the filter chain should be allowed to continue, {@code false} otherwise.
It is called before the chain is actually consulted/executed.
<p/>
The default implementation returns {@code true} always and exists as a template method for subclasses.

@param request  the incoming ServletRequest
@param response the outgoing ServletResponse
@return {@code true} if the filter chain should be allowed to continue, {@code false} otherwise.
@throws Exception if there is any error.
web/src/main/java/org/apache/shiro/web/servlet/AdviceFilter.java