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In Rails 3.0, a Rails::Application object was introduced which is nothing more than an Engine but with the responsibility of coordinating the whole boot process.

Initialization

Rails::Application is responsible for executing all railties and engines initializers. It also executes some bootstrap initializers (check Rails::Application::Bootstrap) and finishing initializers, after all the others are executed (check Rails::Application::Finisher).

Configuration

Besides providing the same configuration as Rails::Engine and Rails::Railtie, the application object has several specific configurations, for example “cache_classes”, “consider_all_requests_local”, “filter_parameters”, “logger” and so forth.

Check Rails::Application::Configuration to see them all.

Routes

The application object is also responsible for holding the routes and reloading routes whenever the files change in development.

Middlewares

The Application is also responsible for building the middleware stack.

Booting process

The application is also responsible for setting up and executing the booting process. From the moment you require “config/application.rb” in your app, the booting process goes like this:

1)  require "config/boot.rb" to setup load paths
2)  require railties and engines
3)  Define Rails.application as "class MyApp::Application < Rails::Application"
4)  Run config.before_configuration callbacks
5)  Load config/environments/ENV.rb
6)  Run config.before_initialize callbacks
7)  Run Railtie#initializer defined by railties, engines and application.
    One by one, each engine sets up its load paths, routes and runs its config/initializers/* files.
8)  Custom Railtie#initializers added by railties, engines and applications are executed
9)  Build the middleware stack and run to_prepare callbacks
10) Run config.before_eager_load and eager_load! if eager_load is true
11) Run config.after_initialize callbacks

Multiple Applications

If you decide to define multiple applications, then the first application that is initialized will be set to Rails.application, unless you override it with a different application.

To create a new application, you can instantiate a new instance of a class that has already been created:

class Application < Rails::Application
end

first_application  = Application.new
second_application = Application.new(config: first_application.config)

In the above example, the configuration from the first application was used to initialize the second application. You can also use the initialize_copy on one of the applications to create a copy of the application which shares the configuration.

If you decide to define rake tasks, runners, or initializers in an application other than Rails.application, then you must run those these manually.

Namespace
Methods
C
E
G
I
K
M
N
R
Constants
INITIAL_VARIABLES = [:config, :railties, :routes_reloader, :reloaders, :routes, :helpers, :app_env_config, :secrets]
 
Attributes
[RW] assets
[R] reloaders
[RW] sandbox
[RW] sandbox?
Class Public methods
new(initial_variable_values = {}, &block)
# File railties/lib/rails/application.rb, line 110
def initialize(initial_variable_values = {}, &block)
  super()
  @initialized       = false
  @reloaders         = []
  @routes_reloader   = nil
  @app_env_config    = nil
  @ordered_railties  = nil
  @railties          = nil
  @message_verifiers = {}

  Rails.application ||= self

  add_lib_to_load_path!
  ActiveSupport.run_load_hooks(:before_configuration, self)

  initial_variable_values.each do |variable_name, value|
    if INITIAL_VARIABLES.include?(variable_name)
      instance_variable_set("@#{variable_name}", value)
    end
  end

  instance_eval(&block) if block_given?
end
Instance Public methods
call(env)

Implements call according to the Rack API. It simply dispatches the request to the underlying middleware stack.

# File railties/lib/rails/application.rb, line 141
def call(env)
  env["ORIGINAL_FULLPATH"] = build_original_fullpath(env)
  env["ORIGINAL_SCRIPT_NAME"] = env["SCRIPT_NAME"]
  super(env)
end
config_for(name)

Convenience for loading config/foo.yml for the current Rails env.

Example:

# config/exception_notification.yml:
production:
  url: http://127.0.0.1:8080
  namespace: my_app_production
development:
  url: http://localhost:3001
  namespace: my_app_development

# config/production.rb
MyApp::Application.configure do
  config.middleware.use ExceptionNotifier, config_for(:exception_notification)
end
# File railties/lib/rails/application.rb, line 206
def config_for(name)
  yaml = Pathname.new("#{paths["config"].existent.first}/#{name}.yml")

  if yaml.exist?
    require "yaml"
    require "erb"
    (YAML.load(ERB.new(yaml.read).result) || {})[Rails.env] || {}
  else
    raise "Could not load configuration. No such file - #{yaml}"
  end
rescue Psych::SyntaxError => e
  raise "YAML syntax error occurred while parsing #{yaml}. "          "Please note that YAML must be consistently indented using spaces. Tabs are not allowed. "          "Error: #{e.message}"
end
console(&blk)

Sends any console called in the instance of a new application up to the console method defined in Rails::Railtie.

# File railties/lib/rails/application.rb, line 268
def console(&blk)
  self.class.console(&blk)
end
env_config()

Stores some of the Rails initial environment parameters which will be used by middlewares and engines to configure themselves.

# File railties/lib/rails/application.rb, line 224
def env_config
  @app_env_config ||= begin
    validate_secret_key_config!

    super.merge({
      "action_dispatch.parameter_filter" => config.filter_parameters,
      "action_dispatch.redirect_filter" => config.filter_redirect,
      "action_dispatch.secret_token" => config.secret_token,
      "action_dispatch.secret_key_base" => secrets.secret_key_base,
      "action_dispatch.show_exceptions" => config.action_dispatch.show_exceptions,
      "action_dispatch.show_detailed_exceptions" => config.consider_all_requests_local,
      "action_dispatch.logger" => Rails.logger,
      "action_dispatch.backtrace_cleaner" => Rails.backtrace_cleaner,
      "action_dispatch.key_generator" => key_generator,
      "action_dispatch.http_auth_salt" => config.action_dispatch.http_auth_salt,
      "action_dispatch.signed_cookie_salt" => config.action_dispatch.signed_cookie_salt,
      "action_dispatch.encrypted_cookie_salt" => config.action_dispatch.encrypted_cookie_salt,
      "action_dispatch.encrypted_signed_cookie_salt" => config.action_dispatch.encrypted_signed_cookie_salt,
      "action_dispatch.cookies_serializer" => config.action_dispatch.cookies_serializer
    })
  end
end
generators(&blk)

Sends any generators called in the instance of a new application up to the generators method defined in Rails::Railtie.

# File railties/lib/rails/application.rb, line 274
def generators(&blk)
  self.class.generators(&blk)
end
inherited(base)
# File railties/lib/rails/application.rb, line 88
def inherited(base)
  super
  base.instance
end
initialized?()

Returns true if the application is initialized.

# File railties/lib/rails/application.rb, line 135
def initialized?
  @initialized
end
initializer(name, opts={}, &block)

Sends the initializers to the initializer method defined in the Rails::Initializable module. Each Rails::Application class has its own set of initializers, as defined by the Initializable module.

# File railties/lib/rails/application.rb, line 256
def initializer(name, opts={}, &block)
  self.class.initializer(name, opts, &block)
end
isolate_namespace(mod)

Sends the isolate_namespace method up to the class method.

# File railties/lib/rails/application.rb, line 279
def isolate_namespace(mod)
  self.class.isolate_namespace(mod)
end
key_generator()

Return the application's KeyGenerator

# File railties/lib/rails/application.rb, line 153
def key_generator
  # number of iterations selected based on consultation with the google security
  # team. Details at https://github.com/rails/rails/pull/6952#issuecomment-7661220
  @caching_key_generator ||=
    if secrets.secret_key_base
      key_generator = ActiveSupport::KeyGenerator.new(secrets.secret_key_base, iterations: 1000)
      ActiveSupport::CachingKeyGenerator.new(key_generator)
    else
      ActiveSupport::LegacyKeyGenerator.new(config.secret_token)
    end
end
message_verifier(verifier_name)

Returns a message verifier object.

This verifier can be used to generate and verify signed messages in the application.

It is recommended not to use the same verifier for different things, so you can get different verifiers passing the verifier_name argument.

Parameters

  • verifier_name - the name of the message verifier.

Examples

message = Rails.application.message_verifier('sensitive_data').generate('my sensible data')
Rails.application.message_verifier('sensitive_data').verify(message)
# => 'my sensible data'

See the +ActiveSupport::MessageVerifier+ documentation for more information.

# File railties/lib/rails/application.rb, line 183
def message_verifier(verifier_name)
  @message_verifiers[verifier_name] ||= begin
    secret = key_generator.generate_key(verifier_name.to_s)
    ActiveSupport::MessageVerifier.new(secret)
  end
end
rake_tasks(&block)

If you try to define a set of rake tasks on the instance, these will get passed up to the rake tasks defined on the application's class.

# File railties/lib/rails/application.rb, line 249
def rake_tasks(&block)
  self.class.rake_tasks(&block)
end
reload_routes!()

Reload application routes regardless if they changed or not.

# File railties/lib/rails/application.rb, line 148
def reload_routes!
  routes_reloader.reload!
end
runner(&blk)

Sends any runner called in the instance of a new application up to the runner method defined in Rails::Railtie.

# File railties/lib/rails/application.rb, line 262
def runner(&blk)
  self.class.runner(&blk)
end