Rails 2.2 主要包含以下几个新的特性：

1、Internationalization by default 默认国际化
2、Stronger etag and last-modified support 更强的etag和最后更新支持
3、Thread safety and a connection pool 线程安全和连接池
4、兼容Ruby 1.9 和 JRuby
5、Better API docs, great guides 更好的API文档和教程  

gem install activesupport-2.2.2.gem
gem install activerecord-2.2.2.gem
gem install actionpack-2.2.2.gem
gem install actionmailer-2.2.2.gem
gem install activeresource-2.2.2.gem
gem install rake-0.8.3.gem
gem install rails-2.2.2.gem   

rails -v // Show Rails 2.2.2 :)

或采用升级方法：
gen update --system
gem install rails

更多信息：Rails 2.2: i18n, HTTP validators, thread safety, JRuby/1.9 compatibility, docs