multi_logger provides a unified way to log messages and events to multiple locations.

There are some loggers provided out of the box: ConsoleLogger and SentryLogger, but there is also a flexible and easy-to-use interface to create your own loggers.

How to use

Install

To use multi_logger, simply add it to your pubspec.yaml file:

dart pub add multi_logger

Initialize

logger = MultiLogger(
  loggers: [
    ConsoleLogger(
      level: LogLevel.trace,
    ),
    SentryLogger(
      level: LogLevel.error,
    ),
  ]
);

It is also possible to use any logger separately. MultiLogger is just an another type of logger implementing logging to multiple sources and sharing absolutely the same interface.

Use

There are 5 levels and corresponding methods to use: trace, debug, info, warning, error and fatal. All of them use the same set of parameters:

  • message: this might be anything, usually logger will use toString() to get a string representation
  • dateTime: optional date/time associated with the log event, current date/time will be used if not provided
  • error: optional error associated with the log event, usually logger will use toString() to get a string representation
  • stackTrace: optional log event stack trace, current stack trace will be used if not provided
  • extra: an arbitrary extra data associated with the log event
logger.info('This is an informational message');

try {
  throw ...;
} catch (error, stackTrace) {
  logger.error(
    'An error happened',
    error: error,
    stackTrace: stackTrace,
  );
}

If you want to filter log events or modify them it's possible to provide a beforeLog callback and return a modified event or null to drop an event completely.

ConsoleLogger(
  beforeLog: (event) {
    // Drop all events with extra data
    return (event.extra != null) ? null : event;
  },
),

Also you can subscribe to log events and their respective outputs from each logger using the provided events stream:

consoleLogger.events.listen((data) {
  final (event, output) = data;
  ...
}

Built-in loggers

There are two built-in loggers provided:

  • ConsoleLogger: logs messages to console with colorized output based on levels, stack traces for errors and logging of extra associated with events
  • SentryLogger: logs messages and errors to Sentry

Note: in order to use SentryLogger Sentry needs to be already initialized.

Custom loggers

You can create you own logger by simply extending Logger class and implementing a single method:

class MyLogger extends Logger {
  MyLogger({super.level});

  @override
  Future<dynamic> logEvent(LogEvent event) async {
    // Your implementation goes here
  }
}

Libraries

multi_logger