diff --git a/README.md b/README.md
index ab9fd91..705e8eb 100644
--- a/README.md
+++ b/README.md
@@ -33,19 +33,19 @@ Build Status
  * 2013.2.19 用户可以删除自己的key
  * 2013.2.21 添加图书搜索API
  * 2013.2.26 添加归还已经借阅图书的API
- * 2013.2.27 修改借书逻辑，由之前的系统自动查找合适人选，变为借书者自行选择合适的拥有书者。
+ * 2013.2.27 修改借书逻辑，由之前的系统自动查找合适人选，变为借书者自行选择合适的拥有书者。修改bookinfo API增加返回所有当前可借的实例信息
 
 #### JSON API使用指南
 
         * GET /api/userinfo/:user_id 用户用户的相关信息
-        * GET /api/bookinfo/:isbn  需要传入书籍的13位ISBN号，获取书籍的相关信息，拥有书籍的用户，和当前可借的用户信息
+        * GET /api/bookinfo/:isbn  需要传入书籍的13位ISBN号，获取书籍的相关信息，拥有书籍的用户，和当前所有可借的用户信息
         * GET /api/books  以列表形式获取图书信息，每页10条信息，如要获取第二页信息地址则为 /api/books/?page=2,依次类推
         * GET /api/book/search/:keyword 图书搜索，最多返回20条相关记录
         * POST /api/auth 客户端使用auth key,进行验证登录，验证成功后，可以使用该key,进行所有需要认证的操作。
           必填参数key,auth在用户中心，点击小锁图片即可进入KEY管理页面。(KEY不区分大小写)
         * POST '/api/books/add', 添加图书，必须填入图书的ISBN(isbn),和Auth key(key)。括号为传递参数的实际名称
         * POST '/api/book/return' 归还已经借阅的图书，必需参数Auth key(key),Book binstance id(instance_id )
-
+        * POST '/api/books/borrow' 借阅图书，必需参数Auth key(key),Book binstance id(instance_id )
 
 #### Road map:
 * 移动客户端的支持，用户可以在手机上查找图书，通过扫描二维码添加图书。
diff --git a/app/controllers/api_controller.rb b/app/controllers/api_controller.rb
index 27b48ba..c63128b 100644
--- a/app/controllers/api_controller.rb
+++ b/app/controllers/api_controller.rb
@@ -9,7 +9,7 @@ class ApiController < ApplicationController
     end
     render json: book.to_json(include: [{:users =>
                                              {except: [:api_key, :email, :created_at]}},
-                                        :available_instance])
+                                        :total_available_instances])
   end
 
   def user_info
@@ -72,6 +72,22 @@ class ApiController < ApplicationController
 
   end
 
+  def borrow_book
+    key = AuthKey.find_by_value params[:key]
+    unless key
+      render json: {status: 'error', message: 'key is invalid,please change an other key.'}
+      return
+    end
+    instance = BookInstance.find_by_id params[:instance_id]
+    if instance!=nil && instance.borrowed? != true
+      user = User.find_by_id key.user_id
+      user.borrow instance
+      render json: {message: 'Borrow book success.', status: 'success'}
+      return
+    end
+    render json: {message: 'Sorry, you can not borrow this book right now.', status: 'error'}
+  end
+
   def return_book
     key = AuthKey.find_by_value params[:key]
     unless key
@@ -79,8 +95,9 @@ class ApiController < ApplicationController
       return
     end
     instance = BookInstance.find_by_id params[:instance_id]
-    if @current_user.borrowed_and_not_returned_books.include? instance
-      @current_user.return_book instance
+    user = User.find_by_id key.user_id
+    if user.borrowed_and_not_returned_books.include? instance
+      user.return_book instance
       render json: {message: 'Return book success.', status: 'success'}
       return
     end
diff --git a/config/routes.rb b/config/routes.rb
index 0ffe5fb..95a076f 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -16,7 +16,7 @@ Libr::Application.routes.draw do
   get '/douban_callback' => 'home#douban_callback'
   get '/qq_callback' => 'home#qq_callback'
   get '/users/:id' => 'user#view'
-  get '/users/:id/edit' =>'user#edit'
+  get '/users/:id/edit' => 'user#edit'
   put '/users/:id' => 'user#update'
   get '/search' => 'search#do_search'
   delete '/users/:user_id/books/:instance_id' => 'user#delete_book'
@@ -28,10 +28,11 @@ Libr::Application.routes.draw do
   get 'api/bookinfo/:isbn' => 'api#book_info'
   get 'api/userinfo/:user_id' => 'api#user_info'
   get 'api/books' => 'api#books'
-  post 'api/auth' =>'api#auth'
-  get 'api/books/search/:keyword'=>'api#search'
+  post 'api/auth' => 'api#auth'
+  get 'api/books/search/:keyword' => 'api#search'
   post 'api/books/add' => 'api#add_book'
-  post  'api/books/return' =>'api#return_book'
+  post 'api/books/return' => 'api#return_book'
+  post 'api/books/borrow' =>'api#borrow_book'
 
   # The priority is based upon order of creation:
   # first created -> highest priority.
diff --git a/lib/utils.rb b/lib/utils.rb
index 1b4d7ce..bed1b16 100644
--- a/lib/utils.rb
+++ b/lib/utils.rb
@@ -1,6 +1,6 @@
 module Utils
   def random_key(length=8)
-    charset = %w{0 1 2 3 4 6 7 9  A B C D E F G H I J K L M N O P Q R S T U V W X Y Z ! @ # $ % & *}
+    charset = %w{0 1 2 3 4 6 7 9  A B C D E F G H I J K L M N O P Q R S T U V W X Y Z ! @  $  *}
     (0...length).map{ charset.to_a[rand(charset.size)] }.join
   end