ImportSelector使用

ImportSelector就比较牛逼了，可以读取annotation的属性来决定要加载哪些Configuration。
以下为ImportSelector的接口定义：

/**
 * Interface to be implemented by types that determine which @{@link Configuration}
 * class(es) should be imported based on a given selection criteria, usually one or more
 * annotation attributes.
 *
 * <p>An {@link ImportSelector} may implement any of the following
 * {@link org.springframework.beans.factory.Aware Aware} interfaces, and their respective
 * methods will be called prior to {@link #selectImports}:
 * <ul>
 * <li>{@link org.springframework.context.EnvironmentAware EnvironmentAware}</li>
 * <li>{@link org.springframework.beans.factory.BeanFactoryAware BeanFactoryAware}</li>
 * <li>{@link org.springframework.beans.factory.BeanClassLoaderAware BeanClassLoaderAware}</li>
 * <li>{@link org.springframework.context.ResourceLoaderAware ResourceLoaderAware}</li>
 * </ul>
 *
 * <p>ImportSelectors are usually processed in the same way as regular {@code @Import}
 * annotations, however, it is also possible to defer selection of imports until all
 * {@code @Configuration} classes have been processed (see {@link DeferredImportSelector}
 * for details).
 *
 * @author Chris Beams
 * @since 3.1
 * @see DeferredImportSelector
 * @see Import
 * @see ImportBeanDefinitionRegistrar
 * @see Configuration
 */
public interface ImportSelector {

    /**
     * Select and return the names of which class(es) should be imported based on
     * the {@link AnnotationMetadata} of the importing @{@link Configuration} class.
     */
    String[] selectImports(AnnotationMetadata importingClassMetadata);

}

selectImports方法的返回值为Configuration主类的全类名。
使用方法和ImportBeanDefinitionRegistrar类似，也是通过import来引入生效的。
举例如下：

@SpringBootApplication
@ComponentScan
@RestController
@EnableConfigurationProperties(RedisProp.class)
@Import(DataConfig3.class)
public class TestApplication

public class DataConfig3 implements ImportSelector{
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        return new String[]{DataConfig.class.getName()};
    }
}