How to create custom logger in Magento 2

In this blog, we will show you the way to create a custom logger to log your own messages into it.

Step 1: Create a logger class

Firstly, create a logger class:

app/code/Magenest/CustomLog/Logger/Logger.php

<?php
namespace Magenest\CustomLog\Logger;

class Logger extends \Monolog\Logger
{

}

app/code/Magenest/CustomLog/Logger/Handler.php

<?php
namespace Magenest\CustomLog\Logger;

use Monolog\Logger;

class Handler extends \Magento\Framework\Logger\Handler\Base
{
   /**
    * Logging level
    * @var int
    */
   protected $loggerType = Logger::NOTICE;

   /**
    * File name
    * @var string
    */
   protected $fileName = '/var/log/magenest_custom_log.log';
}

The file name /var/log/magenest_custom_log.log is a relative path to the magento root folder, it means your log will be stored under <magento_root>/var/log/magenest_custom_log.log

The variable loggerType define the log level can be applied.

Monolog/Logger has the following consts:

DEBUG = 100
INFO = 200
NOTICE = 250
WARNING = 300
ERROR = 400
CRITICAL = 500
ALERT = 550
EMERGENCY = 600

For example, loggerType = NOTICE. It means the logger level will be from “NOTICE” and above such as “WARNING”, “ERROR”, “CRITICAL”, ... And can not log the level “DEBUG” and “INFO”.

Step 2: Declare the logger

The next step is to declare the logger in di.xml.

app/code/Magenest/CustomLog/etc/di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:noNamespaceSchemaLocation="../../../../../lib/internal/Magento/Framework/ObjectManager/etc/config.xsd">
   <type name="Magenest\CustomLog\Logger\Handler">
       <arguments>
           <argument name="filesystem" xsi:type="object">Magento\Framework\Filesystem\Driver\File</argument>
       </arguments>
   </type>
   <type name="Magenest\CustomLog\Logger\Logger">
       <arguments>
           <argument name="name" xsi:type="string">Magenest_Custom_Log</argument>
           <argument name="handlers"  xsi:type="array">
               <item name="system" xsi:type="object">Magenest\CustomLog\Logger\Handler</item>
           </argument>
       </arguments>
   </type>
</config>

You have defined the handler with a unique name. The class Magenest\CustomLog\Logger\Logger will be handled by the handler Magenest\CustomLog\Logger\Handler

That’s it, your logger is ready to use. To test our logger, we will create a controller as the following:

app/code/Magenest/CustomLog/Controller/Index/Index.php

<?php
namespace Magenest\CustomLog\Controller\Index;

use Magenest\CustomLog\Logger\Logger;
use Magento\Framework\App\Action\Action;
use Magento\Framework\App\Action\Context;
use Magento\Framework\View\Result\PageFactory;

class Index extends Action
{
   /**
    * Index action
    *
    * @return $this
    */
   /** @var PageFactory */
   protected $resultPageFactory;

   /**
    * @var Logger
    */
   protected $logger;

   public function __construct(
       Context $context,
       PageFactory $resultPageFactory,
       Logger $logger
   ){
       $this->resultPageFactory = $resultPageFactory;
       $this->logger = $logger;
       parent::__construct($context);
   }

   public function execute()
   {
       $this->logger->error('Log Error');
       $this->logger->emergency('Log Emergency');
       $this->logger->info('Log Info');
       $this->logger->debug('Log Debug');
       $resultPage = $this->resultPageFactory->create();
       return $resultPage;
   }
}

Now you can find the log in var/log/magenest_custom_log.log file