Gateway

从Gateway模式的结构图看有点像Facade, Gateway是为阻隔复杂度向外蔓延而生的，它把复杂的实现封装起来，为其他模块或系统提供一个简单易用的接口。
PEAA中提到，Facade simplifies a more complex API, it's usually done by the writer of the service for general use. Gateway is written by the client for its particular use. Facade的很重要的作用是减少多模块或子系统间通信。