自定义EnableXXX注解类

该自定义注解类用到ImportSelector接口类，它用于判断被@Configuration注解修饰的类是否应该被导入。处理ImportSelector接口时，bean定义已经被加载，但是bean还没有被实例化。

 

DeferredImportSelector接口类：继承于ImportSelector接口类，延迟选择性导入类，在所有被@Configuration注解修饰的类处理完成后才运行。DeferredImportSelector用在处理@Conditional相关的导入时特别有用。

 

EnableXXX >> @Import >> ImportSelector or ImportBeanDefinitionRegistrar >> 注册BeanDefinition

 

1、创建一个配置类

@Configuration
public class SeasyImportSelectorConfig {
	@Bean
	public ServiceConfig serviceConfig(){
		ServiceConfig config = new ServiceConfig();
		config.setName("userService");
		config.setDescription("");
		return config;
	}
}

 

2、创建ImportSelector的子类

/**
 * ImportSelector：有条件的选择被@Configuration注解标注的类进行导入
 */
public class SeasyImportSelector implements ImportSelector, BeanFactoryAware {
	public static final String ANNOTATION_CLASS_NAME = EnableSeasy.class.getName();
	private BeanFactory beanFactory;
	
	/**
	 * 返回被选中的全限定类名的数组
	 * 
	 * @param annotationMetadata 自定义Enable注解类所在类中包含的所有注解类元数据
	 */
	@Override
	public String[] selectImports(AnnotationMetadata annotationMetadata) {
		//获取注解类的所有属性
		MultiValueMap<String, Object> allAnnotationAttributes 
			= annotationMetadata.getAllAnnotationAttributes(ANNOTATION_CLASS_NAME, true);
		for(Iterator<String> it=allAnnotationAttributes.keySet().iterator(); it.hasNext();){
			String key = it.next();
			
			List<Object> list = allAnnotationAttributes.get(key);
			Object value = list.get(0);
			
			if(value instanceof String[] || value.getClass().isArray()){
				System.out.println(key + "=" + Arrays.toString((String[])value));
			}else{
				System.out.println(key + "=" + value);
			}
		}
		
		//获取注解类所在类的所有注解类
		annotationMetadata.getAnnotationTypes().forEach(System.out::println);
		
		//InterfaceNames
		Stream.of(annotationMetadata.getInterfaceNames()).forEach(System.out::println);

		//MemberClassNames
		Stream.of(annotationMetadata.getMemberClassNames()).forEach(System.out::println);
		
		//MetaAnnotationTypes
		annotationMetadata.getMetaAnnotationTypes(ANNOTATION_CLASS_NAME).forEach(System.out::println);

		System.out.println("ClassName: " + annotationMetadata.getClassName());

		return new String[]{SeasyImportSelectorConfig.class.getName()};
	}

	@Override
	public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
		this.beanFactory = beanFactory;
	}
}

 

3、创建自定义注解类

@Documented
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
//@Import注解类：表示将ImportSelector选中返回的类导入到容器中
@Import(SeasyImportSelector.class) 
public @interface EnableSeasy {
	
}

4、创建一个测试用的配置类，并加入自定义 @EnableSeasy 注解类

@Configuration
@EnableSeasy
@ComponentScan
public class EnableSeasyConfig {
	
}

 

5、测试代码

public class EnableSeasyTest {
	public static void main(String[] args) {
		AnnotationConfigApplicationContext applicationContext 
			= new AnnotationConfigApplicationContext(EnableSeasyConfig.class);
		ServiceConfig serviceConfig = applicationContext.getBean(ServiceConfig.class);
        System.out.println(serviceConfig.getName());
	}
}