拜读了用 Rails 搭建微信公众平台 API之后发现，

params[:xml]这个办法在Rails 4里面已经被办掉了，于是就看了一下Rails 4的新特性发现XML Parameter parsing has been sent to a plugin.

http://www.rubydoc.info/github/rails/actionpack-xml_parser

actionpack-xml_parser

A XML parameters parser for Action Pack (removed from core in Rails 4.0)

Installation

Include this gem into your Gemfile:

gem ‘actionpack-xml_parser‘

Then, add ActionDispatch::XmlParamsParser middleware after ActionDispatch::ParamsParser in config/application.rb:

config.middleware.insert_after ActionDispatch::ParamsParser, ActionDispatch::XmlParamsParser

//*********************************************************************************************

Then, add ActionDispatch::XmlParamsParser middleware after ActionDispatch::ParamsParser in config/application.rb:

config.middleware.insert_after ActionDispatch::ParamsParser, ActionDispatch::XmlParamsParser

如图: