_constructFilterFromConfig example

$writer = $this->_constructFromConfig('writer', $config, $this->_defaultWriterNamespace);

        if (!$writer instanceof Zend_Log_Writer_Abstract) {
            $writerName = is_object($writer)
                        ? get_class($writer)
                        : 'The specified writer';
            /** @see Zend_Log_Exception */
            throw new Zend_Log_Exception("{$writerName} does not extend Zend_Log_Writer_Abstract!");
        }

        if (isset($config['filterName'])) {
            $filter = $this->_constructFilterFromConfig($config);
            $writer->addFilter($filter);
        }

        if (isset($config['formatterName'])) {
            $formatter = $this->_constructFormatterFromConfig($config);
            $writer->setFormatter($formatter);
        }

        return $writer;
    }