Handlers

Handlers are the output side of the pipeline.

Built-in handlers across the ecosystem

Console handler

Logger.root.addHandler(
  ConsoleLogHandler(
    filter: const LevelLogFilter(LogLevel.INFO),
    formatter: PrettyLogFormatter(),
  ),
);

ConsoleLogHandler can also try specialized formatter add-ons before the fallback formatter.

Custom handler

When you need your own sink, extend LogHandler:

class AnalyticsLogHandler extends LogHandler {
  const AnalyticsLogHandler({super.filter});

  @override
  void handle(LogRecord record) {
    // Send record to analytics or telemetry backend.
  }
}

Where to attach handlers

Attach app-wide sinks to Logger.root:

Logger.root.addHandler(ConsoleLogHandler());

Attach local sinks only when you intentionally want a subtree-specific output.

Pitfalls

• Logger names are cached, so reused names point to the same logger instance.
• A handler on a parent logger will still see child records unless filtered out.
• Some handlers like FileLogHandler or HistoryLogHandler have their own lifecycle or storage constraints. Read their dedicated sections before using them in production.