失败的案例：cmdp.com 是本地测试地址 @link = params[:link] redirect_to "http://www.cmdp.com" + @link 最后会跳到http://www.cmdp.com
如果是@link = "users/new" redirect_to "http://www.cmdp.com" + @link 则可以正确到达 http://www.cmdp.com/users/new
什么地方有问题呢？ 尝试过将@link = @link.to_s 也不行
params[:link] 应该不是字符串对象， “+”在连接字符串的时候 根据两个值的不同 执行了不同的方法。 包括 to_s 很可能解释成其他的东西了
Started GET "/blogs/new?link=blogs/new" for 127.0.0.1 at 2013-02-27 12:45:32 +0800
Connecting to database specified by database.yml
Processing by BlogsController#new as HTML
Parameters: {"link"=>"blogs/new"}
Redirected to http://www.buychina.devblogs/new
Completed 302 Found in 0ms (ActiveRecord: 0.0ms)
"http://www.buychina.dev/blogs/new"
Started GET "/blogs/new?link=/blogs/new" for 127.0.0.1 at 2013-02-27 12:45:45 +0800
Processing by BlogsController#new as HTML
Parameters: {"link"=>"/blogs/new"}
Redirected to http://www.buychina.dev/blogs/new
Completed 302 Found in 0ms (ActiveRecord: 0.0ms)
"http://www.buychina.dev"
你可以看到，实际上 redirect 了两次，第一次是正确的，第二次由于没有带参数，所以 redirect to root
