The Initializer is responsible for processing the Rails configuration, such as setting the $LOAD_PATH, requiring the right frameworks, initializing logging, and more. It can be run either as a single command that'll just use the default configuration, like this:

Rails::Initializer.run

But normally it's more interesting to pass in a custom configuration through the block running:

Rails::Initializer.run do |config|
  config.frameworks -= [ :action_mailer ]
end

This will use the default configuration options from Rails::Configuration, but allow for overwriting on select areas.

Methods
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Attributes
[R] configuration

The Configuration instance used by this Initializer instance.

[R] gems_dependencies_loaded

Whether or not all the gem dependencies have been met

[R] loaded_plugins

The set of loaded plugins.

Class Public methods
new(configuration)

Create a new Initializer instance that references the given Configuration instance.

# File railties/lib/initializer.rb, line 119
def initialize(configuration)
  @configuration = configuration
  @loaded_plugins = []
end
run(command = :process, configuration = Configuration.new)

Runs the initializer. By default, this will invoke the process method, which simply executes all of the initialization routines. Alternately, you can specify explicitly which initialization routine you want:

Rails::Initializer.run(:set_load_path)

This is useful if you only want the load path initialized, without incurring the overhead of completely loading the entire environment.

# File railties/lib/initializer.rb, line 110
def self.run(command = :process, configuration = Configuration.new)
  yield configuration if block_given?
  initializer = new configuration
  initializer.send(command)
  initializer
end
Instance Public methods
add_gem_load_paths()
# File railties/lib/initializer.rb, line 297
def add_gem_load_paths
  Rails::GemDependency.add_frozen_gem_path
  unless @configuration.gems.empty?
    require "rubygems"
    @configuration.gems.each { |gem| gem.add_load_paths }
  end
end
add_plugin_load_paths()

Adds all load paths from plugins to the global set of load paths, so that code from plugins can be required (explicitly or automatically via ActiveSupport::Dependencies).

# File railties/lib/initializer.rb, line 293
def add_plugin_load_paths
  plugin_loader.add_plugin_load_paths
end
add_support_load_paths()

Add the load paths used by support functions such as the info controller

# File railties/lib/initializer.rb, line 288
def add_support_load_paths
end
after_initialize()
# File railties/lib/initializer.rb, line 611
def after_initialize
  if gems_dependencies_loaded
    configuration.after_initialize_blocks.each do |block|
      block.call
    end
  end
end
check_for_unbuilt_gems()
# File railties/lib/initializer.rb, line 311
    def check_for_unbuilt_gems
      unbuilt_gems = @configuration.gems.select(&:frozen?).reject(&:built?)
      if unbuilt_gems.size > 0
        # don't print if the gems:build rake tasks are being run
        unless $gems_build_rake_task
          abort <<-end_error
The following gems have native components that need to be built
  #{unbuilt_gems.map { |gem| "#{gem.name}  #{gem.requirement}" } * "\n  "}
You're running:
  ruby #{Gem.ruby_version} at #{Gem.ruby}
  rubygems #{Gem::RubyGemsVersion} at #{Gem.path * ', '}
Run `rake gems:build` to build the unbuilt gems.
          end_error
        end
      end
    end
check_gem_dependencies()
# File railties/lib/initializer.rb, line 330
    def check_gem_dependencies
      unloaded_gems = @configuration.gems.reject { |g| g.loaded? }
      if unloaded_gems.size > 0
        @gems_dependencies_loaded = false
        # don't print if the gems rake tasks are being run
        unless $gems_rake_task
          abort <<-end_error
Missing these required gems:
  #{unloaded_gems.map { |gem| "#{gem.name}  #{gem.requirement}" } * "\n  "}
You're running:
  ruby #{Gem.ruby_version} at #{Gem.ruby}
  rubygems #{Gem::RubyGemsVersion} at #{Gem.path * ', '}
Run `rake gems:install` to install the missing gems.
          end_error
        end
      else
        @gems_dependencies_loaded = true
      end
    end
check_ruby_version()

Check for valid Ruby version This is done in an external file, so we can use it from the `rails` program as well without duplication.

# File railties/lib/initializer.rb, line 209
def check_ruby_version
  require 'ruby_version_check'
end
disable_dependency_loading()
# File railties/lib/initializer.rb, line 634
def disable_dependency_loading
  if configuration.cache_classes && !configuration.dependency_loading
    ActiveSupport::Dependencies.unhook!
  end
end
initialize_cache()
# File railties/lib/initializer.rb, line 455
def initialize_cache
  unless defined?(RAILS_CACHE)
    silence_warnings { Object.const_set "RAILS_CACHE", ActiveSupport::Cache.lookup_store(configuration.cache_store) }
    if RAILS_CACHE.respond_to?(:middleware)
      # Insert middleware to setup and teardown local cache for each request
      configuration.middleware.insert_after(:"ActionController::Failsafe", RAILS_CACHE.middleware)
    end
  end
end
initialize_database()

This initialization routine does nothing unless :active_record is one of the frameworks to load (Rails::Configuration#frameworks). If it is, this sets the database configuration from Rails::Configuration#database_configuration and then establishes the connection.

# File railties/lib/initializer.rb, line 435
def initialize_database
  if configuration.frameworks.include?(:active_record)
    ActiveRecord::Base.configurations = configuration.database_configuration
    ActiveRecord::Base.establish_connection
  end
end
initialize_database_middleware()
# File railties/lib/initializer.rb, line 442
def initialize_database_middleware
  if configuration.frameworks.include?(:active_record)
    if configuration.frameworks.include?(:action_controller) &&
        ActionController::Base.session_store.name == 'ActiveRecord::SessionStore'
      configuration.middleware.insert_before :"ActiveRecord::SessionStore", ActiveRecord::ConnectionAdapters::ConnectionManagement
      configuration.middleware.insert_before :"ActiveRecord::SessionStore", ActiveRecord::QueryCache
    else
      configuration.middleware.use ActiveRecord::ConnectionAdapters::ConnectionManagement
      configuration.middleware.use ActiveRecord::QueryCache
    end
  end
end
initialize_dependency_mechanism()

Sets the dependency loading mechanism based on the value of Rails::Configuration#cache_classes.

# File railties/lib/initializer.rb, line 542
def initialize_dependency_mechanism
  ActiveSupport::Dependencies.mechanism = configuration.cache_classes ? :require : :load
end
initialize_encoding()

For Ruby 1.8, this initialization sets $KCODE to 'u' to enable the multibyte safe operations. Plugin authors supporting other encodings should override this behaviour and set the relevant default_charseton ActionController::Base.

For Ruby 1.9, this does nothing. Specify the default encoding in the Ruby shebang line if you don't want UTF-8.

# File railties/lib/initializer.rb, line 427
def initialize_encoding
  $KCODE='u' if RUBY_VERSION < '1.9'
end
initialize_framework_caches()
# File railties/lib/initializer.rb, line 466
def initialize_framework_caches
  if configuration.frameworks.include?(:action_controller)
    ActionController::Base.cache_store ||= RAILS_CACHE
  end
end
initialize_framework_logging()

Sets the logger for Active Record, Action Controller, and Action Mailer (but only for those frameworks that are to be loaded). If the framework's logger is already set, it is not changed, otherwise it is set to use RAILS_DEFAULT_LOGGER.

# File railties/lib/initializer.rb, line 508
def initialize_framework_logging
  for framework in ([ :active_record, :action_controller, :action_mailer ] & configuration.frameworks)
    framework.to_s.camelize.constantize.const_get("Base").logger ||= Rails.logger
  end
  ActiveSupport::Dependencies.logger ||= Rails.logger
  Rails.cache.logger ||= Rails.logger
end
initialize_framework_settings()

Initializes framework-specific settings for each of the loaded frameworks ( Rails::Configuration#frameworks). The available settings map to the accessors on each of the corresponding Base classes.

# File railties/lib/initializer.rb, line 597
def initialize_framework_settings
  configuration.frameworks.each do |framework|
    base_class = framework.to_s.camelize.constantize.const_get("Base")
    configuration.send(framework).each do |setting, value|
      base_class.send("#{setting}=", value)
    end
  end
  configuration.active_support.each do |setting, value|
    ActiveSupport.send("#{setting}=", value)
  end
end
initialize_framework_views()

Sets +ActionController::Base#view_paths+ and +ActionMailer::Base#template_root+ (but only for those frameworks that are to be loaded). If the framework's paths have already been set, it is not changed, otherwise it is set to use Rails::Configuration#view_path.

# File railties/lib/initializer.rb, line 521
def initialize_framework_views
  if configuration.frameworks.include?(:action_view)
    view_path = ActionView::PathSet.type_cast(configuration.view_path)
    ActionMailer::Base.template_root  = view_path if configuration.frameworks.include?(:action_mailer) && ActionMailer::Base.view_paths.blank?
    ActionController::Base.view_paths = view_path if configuration.frameworks.include?(:action_controller) && ActionController::Base.view_paths.blank?
  end
end
initialize_i18n()

Set the i18n configuration from config.i18n but special-case for the load_path which should be appended to what's already set instead of overwritten.

# File railties/lib/initializer.rb, line 575
def initialize_i18n
  configuration.i18n.each do |setting, value|
    if setting == :load_path
      I18n.load_path += value
    else
      I18n.send("#{setting}=", value)
    end
  end
end
initialize_logger()

If the RAILS_DEFAULT_LOGGER constant is already set, this initialization routine does nothing. If the constant is not set, and Rails::Configuration#logger is not nil, this also does nothing. Otherwise, a new logger instance is created at Rails::Configuration#log_path, with a default log level of Rails::Configuration#log_level.

If the log could not be created, the log will be set to output to STDERR, with a log level of WARN.

# File railties/lib/initializer.rb, line 480
def initialize_logger
  # if the environment has explicitly defined a logger, use it
  return if Rails.logger
  unless logger = configuration.logger
    begin
      logger = ActiveSupport::BufferedLogger.new(configuration.log_path)
      logger.level = ActiveSupport::BufferedLogger.const_get(configuration.log_level.to_s.upcase)
      if configuration.environment == "production"
        logger.auto_flushing = false
      end
    rescue StandardError => e
      logger = ActiveSupport::BufferedLogger.new(STDERR)
      logger.level = ActiveSupport::BufferedLogger::WARN
      logger.warn(
        "Rails Error: Unable to access log file. Please ensure that #{configuration.log_path} exists and is chmod 0666. " +
        "The log level has been raised to WARN and the output directed to STDERR until the problem is fixed."
      )
    end
  end
  silence_warnings { Object.const_set "RAILS_DEFAULT_LOGGER", logger }
end
initialize_metal()
# File railties/lib/initializer.rb, line 585
def initialize_metal
  Rails::Rack::Metal.requested_metals = configuration.metals
  Rails::Rack::Metal.metal_paths += plugin_loader.engine_metal_paths
  configuration.middleware.insert_before(
    :"ActionController::ParamsParser",
    Rails::Rack::Metal, :if => Rails::Rack::Metal.metals.any?)
end
initialize_routing()

If Action Controller is not one of the loaded frameworks (Rails::Configuration#frameworks) this does nothing. Otherwise, it loads the routing definitions and sets up loading module used to lazily load controllers (Rails::Configuration#controller_paths).

# File railties/lib/initializer.rb, line 532
def initialize_routing
  return unless configuration.frameworks.include?(:action_controller)
  ActionController::Routing.controller_paths += configuration.controller_paths
  ActionController::Routing::Routes.add_configuration_file(configuration.routes_configuration_file)
  ActionController::Routing::Routes.reload!
end
initialize_time_zone()

Sets the default value for Time.zone, and turns on ActiveRecord::Base#time_zone_aware_attributes. If assigned value cannot be matched to a TimeZone, an exception will be raised.

# File railties/lib/initializer.rb, line 554
def initialize_time_zone
  if configuration.time_zone
    zone_default = Time.__send__(:get_zone, configuration.time_zone)
    unless zone_default
      raise              'Value assigned to config.time_zone not recognized.' +
        'Run "rake -D time" for a list of tasks for finding appropriate time zone names.'
    end
    Time.zone_default = zone_default
    if configuration.frameworks.include?(:active_record)
      ActiveRecord::Base.time_zone_aware_attributes = true
      ActiveRecord::Base.default_timezone = :utc
    end
  end
end
initialize_whiny_nils()

Loads support for “whiny nil” (noisy warnings when methods are invoked on nilvalues) if Rails::Configuration#whiny_nils is true.

# File railties/lib/initializer.rb, line 548
def initialize_whiny_nils
  require('active_support/whiny_nil') if configuration.whiny_nils
end
install_gem_spec_stubs()

If Rails is vendored and RubyGems is available, install stub GemSpecs for Rails, Active Support, Active Record, Action Pack, Action Mailer, and Active Resource. This allows Gem plugins to depend on Rails even when the Gem version of Rails shouldn't be loaded.

# File railties/lib/initializer.rb, line 217
def install_gem_spec_stubs
  unless Rails.respond_to?(:vendor_rails?)
    abort %Q{Your config/boot.rb is outdated: Run "rake rails:update".}
  end
  if Rails.vendor_rails?
    begin; require "rubygems"; rescue LoadError; return; end
    stubs = %w(rails activesupport activerecord actionpack actionmailer activeresource)
    stubs.reject! { |s| Gem.loaded_specs.key?(s) }
    stubs.each do |stub|
      Gem.loaded_specs[stub] = Gem::Specification.new do |s|
        s.name = stub
        s.version = Rails::VERSION::STRING
        s.loaded_from = ""
      end
    end
  end
end
load_application_classes()

Eager load application classes

# File railties/lib/initializer.rb, line 408
def load_application_classes
  return if $rails_rake_task && configuration.dependency_loading
  if configuration.cache_classes
    configuration.eager_load_paths.each do |load_path|
      matcher = /\A#{Regexp.escape(load_path)}(.*)\.rb\Z/
      Dir.glob("#{load_path}/**/*.rb").sort.each do |file|
        require_dependency file.sub(matcher, '\1')
      end
    end
  end
end
load_application_initializers()
# File railties/lib/initializer.rb, line 619
def load_application_initializers
  if gems_dependencies_loaded
    Dir["#{configuration.root_path}/config/initializers/**/*.rb"].sort.each do |initializer|
      load(initializer)
    end
  end
end
load_environment()

Loads the environment specified by Rails::Configuration#environment_path, which is typically one of development, test, or production.

# File railties/lib/initializer.rb, line 378
def load_environment
  silence_warnings do
    return if @environment_loaded
    @environment_loaded = true
    config = configuration
    constants = self.class.constants
    eval(IO.read(configuration.environment_path), binding, configuration.environment_path)
    (self.class.constants - constants).each do |const|
      Object.const_set(const, self.class.const_get(const))
    end
  end
end
load_gems()
# File railties/lib/initializer.rb, line 305
def load_gems
  unless $gems_rake_task
    @configuration.gems.each { |gem| gem.load }
  end
end
load_observers()
# File railties/lib/initializer.rb, line 394
def load_observers
  if gems_dependencies_loaded && configuration.frameworks.include?(:active_record)
    ActiveRecord::Base.instantiate_observers
  end
end
load_plugins()

Loads all plugins in config.plugin_paths. plugin_pathsdefaults to vendor/pluginsbut may also be set to a list of paths, such as

config.plugin_paths = ["#{RAILS_ROOT}/lib/plugins", "#{RAILS_ROOT}/vendor/plugins"]

In the default implementation, as each plugin discovered in plugin_pathsis initialized:

  • its libdirectory, if present, is added to the load path (immediately after the applications lib directory)

  • init.rbis evaluated, if present

After all plugins are loaded, duplicates are removed from the load path. If an array of plugin names is specified in config.plugins, only those plugins will be loaded and they plugins will be loaded in that order. Otherwise, plugins are loaded in alphabetical order.

if config.plugins ends contains :all then the named plugins will be loaded in the given order and all other plugins will be loaded in alphabetical order

# File railties/lib/initializer.rb, line 368
def load_plugins
  plugin_loader.load_plugins
end
load_view_paths()
# File railties/lib/initializer.rb, line 400
def load_view_paths
  if configuration.frameworks.include?(:action_view)
    ActionController::Base.view_paths.load! if configuration.frameworks.include?(:action_controller)
    ActionMailer::Base.view_paths.load! if configuration.frameworks.include?(:action_mailer)
  end
end
plugin_loader()
# File railties/lib/initializer.rb, line 372
def plugin_loader
  @plugin_loader ||= configuration.plugin_loader.new(self)
end
preload_frameworks()

Preload all frameworks specified by the Rails::Configuration#frameworks. Used by Passenger to ensure everything's loaded before forking and to avoid autoload race conditions in JRuby.

# File railties/lib/initializer.rb, line 277
def preload_frameworks
  if configuration.preload_frameworks
    configuration.frameworks.each do |framework|
      # String#classify and #constantize aren't available yet.
      toplevel = Object.const_get(framework.to_s.gsub(/(?:^|_)(.)/) { $1.upcase })
      toplevel.load_all! if toplevel.respond_to?(:load_all!)
    end
  end
end
prepare_dispatcher()
# File railties/lib/initializer.rb, line 627
def prepare_dispatcher
  return unless configuration.frameworks.include?(:action_controller)
  require 'dispatcher' unless defined?(::Dispatcher)
  Dispatcher.define_dispatcher_callbacks(configuration.cache_classes)
  Dispatcher.run_prepare_callbacks
end
process()

Sequentially step through all of the available initialization routines, in order (view execution order in source).

# File railties/lib/initializer.rb, line 126
def process
  Rails.configuration = configuration
  check_ruby_version
  install_gem_spec_stubs
  set_load_path
  add_gem_load_paths
  require_frameworks
  set_autoload_paths
  add_plugin_load_paths
  load_environment
  preload_frameworks
  initialize_encoding
  initialize_database
  initialize_cache
  initialize_framework_caches
  initialize_logger
  initialize_framework_logging
  initialize_dependency_mechanism
  initialize_whiny_nils
  initialize_time_zone
  initialize_i18n
  initialize_framework_settings
  initialize_framework_views
  initialize_metal
  add_support_load_paths
  check_for_unbuilt_gems
  load_gems
  load_plugins
  # pick up any gems that plugins depend on
  add_gem_load_paths
  load_gems
  check_gem_dependencies
  # bail out if gems are missing - note that check_gem_dependencies will have
  # already called abort() unless $gems_rake_task is set
  return unless gems_dependencies_loaded
  load_application_initializers
  # the framework is now fully initialized
  after_initialize
  # Setup database middleware after initializers have run
  initialize_database_middleware
  # Prepare dispatcher callbacks and run 'prepare' callbacks
  prepare_dispatcher
  # Routing must be initialized after plugins to allow the former to extend the routes
  initialize_routing
  # Observers are loaded after plugins in case Observers or observed models are modified by plugins.
  load_observers
  # Load view path cache
  load_view_paths
  # Load application classes
  load_application_classes
  # Disable dependency loading during request cycle
  disable_dependency_loading
  # Flag initialized
  Rails.initialized = true
end
require_frameworks()

Requires all frameworks specified by the Rails::Configuration#frameworks list. By default, all frameworks (Active Record, Active Support, Action Pack, Action Mailer, and Active Resource) are loaded.

# File railties/lib/initializer.rb, line 267
def require_frameworks
  configuration.frameworks.each { |framework| require(framework.to_s) }
rescue LoadError => e
  # Re-raise as RuntimeError because Mongrel would swallow LoadError.
  raise e.to_s
end
set_autoload_paths()

Set the paths from which Rails will automatically load source files, and the load_once paths.

# File railties/lib/initializer.rb, line 248
def set_autoload_paths
  ActiveSupport::Dependencies.autoload_paths = configuration.autoload_paths.uniq
  ActiveSupport::Dependencies.autoload_once_paths = configuration.autoload_once_paths.uniq
  extra = ActiveSupport::Dependencies.autoload_once_paths - ActiveSupport::Dependencies.autoload_paths
  unless extra.empty?
    abort <<-end_error
      autoload_once_paths must be a subset of the autoload_paths.
      Extra items in autoload_once_paths: #{extra * ','}
    end_error
  end
  # Freeze the arrays so future modifications will fail rather than do nothing mysteriously
  configuration.autoload_once_paths.freeze
end
set_load_path()

Set the $LOAD_PATHbased on the value of Rails::Configuration#autoload_paths. Duplicates are removed.

# File railties/lib/initializer.rb, line 240
def set_load_path
  load_paths = configuration.autoload_paths + configuration.framework_paths
  load_paths.reverse_each { |dir| $LOAD_PATH.unshift(dir) if File.directory?(dir) }
  $LOAD_PATH.uniq!
end