To filter before all writers, you can add any number of Filters to a
Log object using the addFilter() method:
<?php
$logger = new Zend_Log();
$writer = new Zend_Log_Writer_Stream('php://output');
$logger->addWriter($writer);
$filter = new Zend_Log_Filter_Priority(Zend_Log::CRIT);
$logger->addFilter($filter);
// blocked
$logger->info('Informational message');
// logged
$logger->emerg('Emergency message');
When you add one or more Filters to the Log object, the message must pass through all of the Filters before any Writers receives it.