一个简单的3层架构例子，有接口的实例等。这里没有数据库操作层是实例，但通过里面的框架，你可以很清晰的认识到3层架构的一些本质内容。-A simple example of the 3-tier structure, there are examples of such interfaces. There are no database operations are examples of layer, but inside the fr a mework, you can very clearl