How to use Monolog to write Logs
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How to use Monolog to write Logs
Monolog is a logging library for PHP 5.3 used by Symfony2. It is inspired by the Python LogBook library.
Usage
To log a message simply get the logger service from the container in
your controller:
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public function indexAction()
{
$logger = $this->get('logger');
$logger->info('I just got the logger');
$logger->error('An error occurred');
// ...
}The logger service has different methods for different logging levels.
See LoggerInterface for details
on which methods are available.
Handlers and Channels: Writing logs to different Locations
In Monolog each logger defines a logging channel, which organizes your log messages into different "categories". Then, each channel has a stack of handlers to write the logs (the handlers can be shared).
Tip
When injecting the logger in a service you can use a custom channel control which "channel" the logger will log to.
The basic handler is the StreamHandler which writes logs in a stream
(by default in the app/logs/prod.log in the prod environment and
app/logs/dev.log in the dev environment).
Monolog comes also with a powerful built-in handler for the logging in
prod environment: FingersCrossedHandler. It allows you to store the
messages in a buffer and to log them only if a message reaches the
action level (error in the configuration provided in the Standard
Edition) by forwarding the messages to another handler.
Using several handlers
The logger uses a stack of handlers which are called successively. This allows you to log the messages in several ways easily.
- YAML
- XML
- PHP
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# app/config/config.yml
monolog:
handlers:
applog:
type: stream
path: /var/log/symfony.log
level: error
main:
type: fingers_crossed
action_level: warning
handler: file
file:
type: stream
level: debug
syslog:
type: syslog
level: errorThe above configuration defines a stack of handlers which will be called in the order where they are defined.
Tip
The handler named "file" will not be included in the stack itself as
it is used as a nested handler of the fingers_crossed handler.
Note
If you want to change the config of MonologBundle in another config file you need to redefine the whole stack. It cannot be merged because the order matters and a merge does not allow to control the order.
Changing the formatter
The handler uses a Formatter to format the record before logging
it. All Monolog handlers use an instance of
Monolog\Formatter\LineFormatter by default but you can replace it
easily. Your formatter must implement
Monolog\Formatter\FormatterInterface.
- YAML
- XML
- PHP
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# app/config/config.yml
services:
my_formatter:
class: Monolog\Formatter\JsonFormatter
monolog:
handlers:
file:
type: stream
level: debug
formatter: my_formatterAdding some extra data in the log messages
Monolog allows to process the record before logging it to add some extra data. A processor can be applied for the whole handler stack or only for a specific handler.
A processor is simply a callable receiving the record as its first argument.
Processors are configured using the monolog.processor DIC tag. See the
reference about it.
Adding a Session/Request Token
Sometimes it is hard to tell which entries in the log belong to which session and/or request. The following example will add a unique token for each request using a processor.
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namespace Acme\MyBundle;
use Symfony\Component\HttpFoundation\Session\Session;
class SessionRequestProcessor
{
private $session;
private $token;
public function __construct(Session $session)
{
$this->session = $session;
}
public function processRecord(array $record)
{
if (null === $this->token) {
try {
$this->token = substr($this->session->getId(), 0, 8);
} catch (\RuntimeException $e) {
$this->token = '????????';
}
$this->token .= '-' . substr(uniqid(), -8);
}
$record['extra']['token'] = $this->token;
return $record;
}
}- YAML
- XML
- PHP
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# app/config/config.yml
services:
monolog.formatter.session_request:
class: Monolog\Formatter\LineFormatter
arguments:
- "[%%datetime%%] [%%extra.token%%] %%channel%%.%%level_name%%: %%message%%\n"
monolog.processor.session_request:
class: Acme\MyBundle\SessionRequestProcessor
arguments: ["@session"]
tags:
- { name: monolog.processor, method: processRecord }
monolog:
handlers:
main:
type: stream
path: "%kernel.logs_dir%/%kernel.environment%.log"
level: debug
formatter: monolog.formatter.session_requestNote
If you use several handlers, you can also register the processor at the handler level instead of globally.
