azhugrov / log4dart

Slf4J inspired log implementation for Dart

Log4Dart

Log4Dart is a logger for Dart inspired by Slf4J.

The logger and its appender are interfaces and thus supports multiple implementations. The following implementations are included

• ConsoleAppender Appender that logs to the console
• file/FileAppender Appender that logs to a file (this appender is not enabled by default as it depends on dart:io)
• LoggerImpl Logger implementation with multiple appenders and diagnostic/tracing support

Getting started

The logger is accessed through the LoggerFactory

class MyClass {
  final Logger _logger;

  MyClass(): _logger = LoggerFactory.getLogger("MyClass");

  someMethod() {
    _logger.info("a info message");
  }
}

Log configuration

By default the LoggerFactory will return a logger that logs to the console, with all log levels enabled. If you need a different logger or dislike the default settings then you can configure the LoggerFactory's builder function.

typedef Logger LoggerBuilder(String loggerName);

This is the method invoked by the factory when asked for a logger. The following example uses a LoggerBuilder to disable debug messages:

LoggerFactory.builder = (name) => new LoggerImpl(name, debugEnabled:false); 

You can use this to return different loggers for different classes

LoggerFactory.builder = (name) {
  if(name == "ClassThatMakesAllotOfNoise") return new LoggerImpl(name, debugEnabled:false, infoEnabled:false);
  if(name == "ClassWithProblems") return new LoggerImpl(name, debugEnabled:true);
  // default logger for the rest
  return new LoggerImpl(name, debugEnabled:false, appenders:[new FileAppender("log.txt")]);
}; 

For more information see the TestRunner.dart class in the test folder

Diagnostic support

The logger supports nested diagnostic contexts which can be used to track application state like this

logger.putContext("context-name", "context-message");
try {
  // log messages from now gets added a context-message
  :
  logger.debug("something important happend");
} finally {
  // stop logging with context-message
  logger.removeContext("context-name");
}

A running example of this can be seen in the ContextLogTest.dart class in the test folder.

TODO

Some missing stuff (feel free to add more):

1. Generate DartDoc for Logger and Appender interface
2. Create a Dart version of sprintf and use it for implementing the formatters
3. Figure out how best to configure the log output format
4. When reflection arrives in Dart add ability to show the class/line where the log message originated

feel free to send in patched for these (or other features you miss).

License

BSD License (Same as Dart itself). See LICENSE file.