Step1: Gemfile中加入gem 'devise'

Step3: rails g devise:install

这一步执行完后命令行会提醒要手动进行如下动作：

===============================================================================

Some setup you must do manually if you haven't yet:

1. Ensure you have defined default url options in your environments files. Here
is an example of default_url_options appropriate for a development environment
in config/environments/development.rb:

config.action_mailer.default_url_options = { host: 'localhost', port: 3000 }

In production, :host should be set to the actual host of your application.

2. Ensure you have defined root_url to *something* in your config/routes.rb.
For example:

root to: "home#index"

3. Ensure you have flash messages in app/views/layouts/application.html.erb.
For example:

<p class="notice"><%= notice %></p>
<p class="alert"><%= alert %></p>

4. You can copy Devise views (for customization) to your app by running:

rails g devise:views

Step4:  rails g devise User

Step6: rake db:migrate

最后，我们可以看看generator在router.rb文件中的devise_for都产生了什么路由.我们可以通过rake routes，结果如下:

可以把devise的登录页面作为系统首页，设置方式为在routes.rb文件中设置如下信息：

devise_scope :user do
    root to: "devise/sessions#new"
  end

或者

devise_scope :user do

unauthenticated :user do
        root to: "devise/sessions#new",as: :unauthenticated_root #设定登录页为系统默认首页
    end
    authenticated :user do
        root to: "homes#index",as: :authenticated_root #设定系统登录后首页
    end

end

application_controlller中加入以下代码

before_action :authenticate_user!     #权限控制,管控仅登录用户方可访问login页面以外内容