对于每一个定制服务，都应该有一个相对应的定制服务工厂类。
For each custom service, there should be a corresponding custom service factory class.
实现了在定制服务接口中声明的方法的类。
Classes that implement the methods declared in custom service interfaces.
Developer应该为每个定制服务提供一个接口类和实现类。
Developer should provide an interface class and implementation class for each custom service.
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