Add stranger and initial stay seconds at first and default is 0.

app/controllers/application_controller.rb

@@ -2,4 +2,16 @@ class ApplicationController < ActionController::Base
   # Prevent CSRF attacks by raising an exception.
   # For APIs, you may want to use :null_session instead.
   protect_from_forgery with: :exception
+
+  before_filter :initial_or_add_stay_time
+
+  def initial_or_add_stay_time
+  	if current_user.present?
+
+  	else
+  		@stranger = Stranger.find_or_create_by(session_id: session['session_id'])
+  		@stranger.stay_seconds += 1
+  		@stranger.save
+  	end
+  end
 end

app/controllers/home_controller.rb

@@ -3,8 +3,8 @@ def index
   	if current_user.present?
   		@greeting = "#{current_user.name} 谢谢你登陆了我们网站！你已经登陆了#{current_user.sign_in_count}次了，总共登陆时间是?分钟了。"
   	else
-  		@greeting = "你好，陌生人！你没有登陆，或者你还没有注册，但是你已经浏览这个页面?分钟了。"
+  		@greeting = "你好，陌生人！你没有登陆，或者你还没有注册，但是你已经浏览这个页面#{(@stranger.stay_seconds/60).round(1)}分钟了。"
   	end
-  	@stat = "现在总共有#{User.all.size}个注册用户在查看这个网站，有?个陌生人在查看这个网站。"
+  	@stat = "现在总共有#{User.all.size}个注册用户在查看这个网站，有#{Stranger.where(updated_at: 5.minutes.ago).size}个陌生人在查看这个网站。"
   end
 end

app/models/stranger.rb

@@ -0,0 +1,3 @@
+class Stranger < ActiveRecord::Base
+  validates :session_id, presence: true, uniqueness: true, :length => { :minimum => 2 }
+end

db/migrate/20150330141141_create_strangers.rb

@@ -0,0 +1,10 @@
+class CreateStrangers < ActiveRecord::Migration
+  def change
+    create_table :strangers do |t|
+      t.string :session_id
+      t.integer :stay_seconds, :null => false, :default => 0
+
+      t.timestamps
+    end
+  end
+end

db/schema.rb

@@ -11,7 +11,14 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20131121162928) do
+ActiveRecord::Schema.define(version: 20150330141141) do
+
+  create_table "strangers", force: true do |t|
+    t.string   "session_id"
+    t.integer  "stay_seconds", default: 0, null: false
+    t.datetime "created_at"
+    t.datetime "updated_at"
+  end
 
   create_table "users", force: true do |t|
     t.string   "name",                   default: "", null: false