Spring boot 梳理 - Configuration Class

1. 推荐使用 Java-based configuration ，也可以使用xml
2.  we generally recommend that your primary source be a single @Configuration class. Usually the class that defines the main method is a good candidate as the primary @Configuration
3. Importing Additional Configuration Classes

   1. You need not put all your @Configuration into a single class. 
      The @Import annotation can be used to import additional configuration classes. 
      Alternatively, you can use @ComponentScan to automatically pick up 
      all Spring components, including @Configuration classes.

4. Importing XML Configuration

   1. If you absolutely must use XML based configuration,
       we recommend that you still start with a @Configuration class. 
      You can then use an @ImportResource annotation to load XML configuration files.