Log4jruby

Log4jruby provides an interface mostly compatible with the standard ruby Logger but backed by Log4j 2. This makes the granular log output configuration, stacktrace output, and other facilities of log4j available to Java and Ruby code alike. For projects that extend/integrate Java already dependent on log4j, it allows log configuration for Java and Ruby code in one spot.

• Automatic stacktrace output (including nested causes) for logged Java and Ruby exceptions
• Configure Java and Ruby logging together (e.g a single log4j2.properties file) and gain log4j features such as runtime output targets for Ruby code.
• Ability to configure logging per distinct logger name (typically a class)
• Supports inclusion of filename, line number, and method name in log messages via ThreadContext. Note: tracing must be enabled.
• High level support for class based logging via the enable_logger macro.
• Compatible with the Rails logging.

Usage and examples

Enable class level logging via enable_logger

 require 'log4jruby'

 class MyClass
   enable_logger

   class << self
     def my_class_method
       logger.info("hello from class method")
     end
   end

   def my_method
     logger.info("hello from instance method")
   end
 end

Custom logger name

logger = Log4jruby::Logger.get('my.logger')
logger.debug('something')

Log4jruby logger names are prefixed with .jruby.

e.g. log4j2.properties

See examples/log4j2.properties for complete example

 ...
 # JRuby logger
logger.jruby.name = jruby
logger.jruby.level = debug
logger.jruby.additivity = false
logger.jruby.appenderRef.stdout.ref = JRuby

Inclusion of filename, line number, and method name in log messages via ThreadContext

e.g.

appender.jruby.layout.pattern = %d %5p %c %X{methodName}:%X{lineNumber} %m%throwable%n

enable tracing globally

Log4jruby::Logger.root.tracing = true

or for specific logger

Log4jruby::Logger.get('MyClass', tracing: true)

produces log statements like:

2022-08-12 17:36:05,819 DEBUG jruby.MyClass foo:20 -- : hello from foo

Exceptions are logged with backtraces

> ruby ./examples/nested_ruby_exceptions.rb
2022-08-25 19:50:47,050 ERROR jruby.test <main>:31 -- : raised from foo org.jruby.exceptions.RuntimeError: (RuntimeError) raised from foo
	at $_dot_.examples.nested_ruby_exceptions.foo(./examples/nested_ruby_exceptions.rb:15)
	at $_dot_.examples.nested_ruby_exceptions.<main>(./examples/nested_ruby_exceptions.rb:29)
Caused by: org.jruby.exceptions.RuntimeError: (RuntimeError) raised from bar
	at $_dot_.examples.nested_ruby_exceptions.bar(./examples/nested_ruby_exceptions.rb:21)
	at $_dot_.examples.nested_ruby_exceptions.foo(./examples/nested_ruby_exceptions.rb:13)
	... 1 more
Caused by: org.jruby.exceptions.RuntimeError: (RuntimeError) raised from baz
	at $_dot_.examples.nested_ruby_exceptions.baz(./examples/nested_ruby_exceptions.rb:25)
	at $_dot_.examples.nested_ruby_exceptions.bar(./examples/nested_ruby_exceptions.rb:19)
	... 2 more

logger.warn(exception)

logger.warn { exception }

logger.error(msg) { exception)

See additional examples in log4jruby/examples.

Configuration

Configuring log4j is left to the client via the standard log4j configuration process.

E.g.

Create a log4j2.properties file and make sure it is available in your classpath.

The log4j-api-2.n.jar and log4j-core-2.n.jars must be found in your classpath when log4jruby is loaded.

• Place files somewhere already in your classpath such as $TOMCAT/lib for Tomcat.
• Configure classpath via JAVA_OPTS
• Amend $CLASSPATH at runtime before loading log4jruby. See examples/setup.rb.

Note: If you're using bundler, you can specify gem 'log4jruby', require: false in your Gemfile to delay loading the gem too early.

In a Rails application, add the following in config/application.rb or the appropriate config/environments file.

 config.logger = ActiveSupport::TaggedLogging.new(Log4jruby::Logger.get('MyApp'))

or older versions of Rails

 config.logger = Log4jruby::Logger.get('MyApp')

Formatters

See formatter in the Ruby ::Logger docs

Log4jruby passes the same arguments to a formatter as would be passed using the standard Ruby Logger given the same logging invocations.

The default Log4jruby formatter outputs progname and msg only (as opposed to the default formatter of the Ruby Logger). Severity, timestamp, and backtraces are handed according to your Log4j configuration. E.g. PatternLayout.

• For JRuby versions < 9.3, Ruby exceptions are not passed directly to the Throwable arg of log4j. Instead, backtraces are included in the log message by the default formatter. This means that %throwable in the log4j config will not affect ruby exceptions for Jruby < 9.3.

The output of the formatter is passed as the message parameter of the [Log4j log methods](https://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/Category.html#log(org.apache.log4j.Priority,%20java.lang.Object).

Development

Install log4j for tests and examples

rake dev:java_deps

e.g.

ruby ./examples/simple.rb

IRB

bundle exec irb
irb(main):002:0> require './examples/setup.rb'
irb(main):003:0> require 'log4jruby'
irb(main):006:0> Log4jruby::Logger.root.debug('test')
DEBUG jruby : - test