我在跟Ruby on Rails Tutorail学习ruby on rails，然而在到了安装bundle后，设置本地服务器的阶段，输入rails server命令后出现了以下问题：
Yuans-MacBook-Pro:first_app Musen$ rails server
=> Booting WEBrick
=> Rails 4.0.8 application starting in development on http://0.0.0.0:3000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
Exiting
/Users/Musen/rails_projects/first_app/config/environments/development.rb:1:in `<top (required)>': undefined method `configure' for #<FirstApp::Application:0x007feacc922200> (NoMethodError)
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@global/gems/activesupport-4.0.8/lib/active_support/dependencies.rb:229:in `require'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@global/gems/activesupport-4.0.8/lib/active_support/dependencies.rb:229:in `block in require'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@global/gems/activesupport-4.0.8/lib/active_support/dependencies.rb:214:in `load_dependency'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@global/gems/activesupport-4.0.8/lib/active_support/dependencies.rb:229:in `require'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@railstutorial_rails_4_0/gems/railties-4.0.8/lib/rails/engine.rb:591:in `block (2 levels) in <class:Engine>'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@railstutorial_rails_4_0/gems/railties-4.0.8/lib/rails/engine.rb:590:in `each'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@railstutorial_rails_4_0/gems/railties-4.0.8/lib/rails/engine.rb:590:in `block in <class:Engine>'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@railstutorial_rails_4_0/gems/railties-4.0.8/lib/rails/initializable.rb:30:in `instance_exec'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@railstutorial_rails_4_0/gems/railties-4.0.8/lib/rails/initializable.rb:30:in `run'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@railstutorial_rails_4_0/gems/railties-4.0.8/lib/rails/initializable.rb:55:in `block in run_initializers'
from /Users/Musen/.rvm/rubies/ruby-2.0.0-p481/lib/ruby/2.0.0/tsort.rb:150:in `block in tsort_each'
from /Users/Musen/.rvm/rubies/ruby-2.0.0-p481/lib/ruby/2.0.0/tsort.rb:183:in `block (2 levels) in each_strongly_connected_component'
from /Users/Musen/.rvm/rubies/ruby-2.0.0-p481/lib/ruby/2.0.0/tsort.rb:210:in `block (2 levels) in each_strongly_connected_component_from'
from /Users/Musen/.rvm/rubies/ruby-2.0.0-p481/lib/ruby/2.0.0/tsort.rb:219:in `each_strongly_connected_component_from'
from /Users/Musen/.rvm/rubies/ruby-2.0.0-p481/lib/ruby/2.0.0/tsort.rb:209:in `block in each_strongly_connected_component_from'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@railstutorial_rails_4_0/gems/railties-4.0.8/lib/rails/initializable.rb:44:in `each'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@railstutorial_rails_4_0/gems/railties-4.0.8/lib/rails/initializable.rb:44:in `tsort_each_child'
from /Users/Musen/.rvm/rubies/ruby-2.0.0-p481/lib/ruby/2.0.0/tsort.rb:203:in `each_strongly_connected_component_from'
from /Users/Musen/.rvm/rubies/ruby-2.0.0-p481/lib/ruby/2.0.0/tsort.rb:182:in `block in each_strongly_connected_component'
from /Users/Musen/.rvm/rubies/ruby-2.0.0-p481/lib/ruby/2.0.0/tsort.rb:180:in `each'
from /Users/Musen/.rvm/rubies/ruby-2.0.0-p481/lib/ruby/2.0.0/tsort.rb:180:in `each_strongly_connected_component'
from /Users/Musen/.rvm/rubies/ruby-2.0.0-p481/lib/ruby/2.0.0/tsort.rb:148:in `tsort_each'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@railstutorial_rails_4_0/gems/railties-4.0.8/lib/rails/initializable.rb:54:in `run_initializers'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@railstutorial_rails_4_0/gems/railties-4.0.8/lib/rails/application.rb:215:in `initialize!'
from /Users/Musen/rails_projects/first_app/config/environment.rb:5:in `<top (required)>'
from /Users/Musen/rails_projects/first_app/config.ru:3:in `require'
from /Users/Musen/rails_projects/first_app/config.ru:3:in `block in <main>'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@global/gems/rack-1.5.2/lib/rack/builder.rb:55:in `instance_eval'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@global/gems/rack-1.5.2/lib/rack/builder.rb:55:in `initialize'
from /Users/Musen/rails_projects/first_app/config.ru:in `new'
from /Users/Musen/rails_projects/first_app/config.ru:in `<main>'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@global/gems/rack-1.5.2/lib/rack/builder.rb:49:in `eval'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@global/gems/rack-1.5.2/lib/rack/builder.rb:49:in `new_from_string'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@global/gems/rack-1.5.2/lib/rack/builder.rb:40:in `parse_file'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@global/gems/rack-1.5.2/lib/rack/server.rb:277:in `build_app_and_options_from_config'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@global/gems/rack-1.5.2/lib/rack/server.rb:199:in `app'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@railstutorial_rails_4_0/gems/railties-4.0.8/lib/rails/commands/server.rb:48:in `app'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@global/gems/rack-1.5.2/lib/rack/server.rb:314:in `wrapped_app'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@railstutorial_rails_4_0/gems/railties-4.0.8/lib/rails/commands/server.rb:75:in `start'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@railstutorial_rails_4_0/gems/railties-4.0.8/lib/rails/commands.rb:76:in `block in <top (required)>'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@railstutorial_rails_4_0/gems/railties-4.0.8/lib/rails/commands.rb:71:in `tap'
from /Users/Musen/.rvm/gems/ruby-2.0.0-p481@railstutorial_rails_4_0/gems/railties-4.0.8/lib/rails/commands.rb:71:in `<top (required)>'
from bin/rails:4:in `require'
from bin/rails:4:in `<main> ’
我在之前曾经安装然后卸载了最新版的rails。根据网上的一些答案，这是因为用新版rails生产的项目语法不同，我更改了把app/config/enviroment.rb里的第一行的 Rails.application.configure do 改成 FirstApp.application.configure do后，再输入 rails server,返回的 undefined method 变成了 undefined method 'application'。
我用的是Mac，系统是Maverick。 求解 T T
解决了。可以参考Stack Overflow上的Error launching Rails server: undefined method 'configure',是新版rails不兼容带来的问题。