app.rb

require 'log4j.jar'

Java::org.apache.log4j.PropertyConfigurator.configure(File.expand_path(File.join(File.dirname(__FILE__), 'log4j.properties')))

$APP_LOG = Java::org.apache.log4j.Logger.getLogger('myapp')

class Foo < Sinatra::Base
  configure do
    disable :raise_errors, :dump_errors, :logging, :show_exceptions
    enable :method_override, :static
  end
  
  after do
    $APP_LOG.info "in the after block"
  end

  error do
    $APP_LOG.error "#{$!}: #{$@.join("\n")}"
  end
  
  post '/' do
    raise 'post error'
  end

  get '/' do
  	raise 'get error'
  end
end

config.ru

require 'rubygems'
require 'bundler/setup'
require 'sinatra'
$:.unshift File.dirname(__FILE__)
disable :raise_errors, :dump_errors, :logging, :show_exceptions, :run
require 'app'
run Foo

Gemfile

source 'http://rubygems.org'
gem 'sinatra'

log4j.properties

# Set root category priority to INFO and its only appender to CONSOLE.
log4j.rootCategory=INFO, CONSOLE, LOGFILE
#log4j.rootCategory=INFO, CONSOLE, LOGFILE

# Set the enterprise logger category to FATAL and its only appender to CONSOLE.
log4j.logger.org.apache.axis.enterprise=FATAL, CONSOLE

# CONSOLE is set to be a ConsoleAppender using a PatternLayout.
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.Threshold=INFO
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=- %m%n

# LOGFILE is set to be a File appender using a PatternLayout.
log4j.appender.LOGFILE=org.apache.log4j.RollingFileAppender
log4j.appender.LOGFILE.File=app.log
log4j.appender.LOGFILE.Append=true
log4j.appender.LOGFILE.Threshold=INFO
log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout
log4j.appender.LOGFILE.layout.ConversionPattern=%-10r %d{ISO8601} [%t] %-5p %c %x - %m%n