Filter is a piece of code that is configured to be executed before and/or after a controller action executes. For example, an access control filter may be executed to ensure that the user is authenticated before executing the requested action; a performance filter may be used to measure the time spent executing the action.
An action can have multiple filters. The filters are executed in the order that they appear in the filter list. A filter can prevent the execution of the action and the rest of the unexecuted filters.
A filter can be defined as a controller class method. The method name must begin with filter. For example, a method named filterAccessControl defines a filter named accessControl. The filter method must have the right signature:
public function filterAccessControl($filterChain)
{
// call $filterChain->run() to continue filter and action execution
}