@Import注解

1 注解定义

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Import {
    Class<?>[] value();
}

@Import注解由@Target({ElementType.TYPE})限制只能用在类上；
@Import注解用来导入配置类或者一些需要前置加载的类到IOC容器中。

2 @Import使用

2.1 直接填入需要加载的类

@Import({ 类名.class , 类名.class... })

示例：

public class Consumer {

    public void consume(String str) {
        System.out.println("INFO:" + str);
    }
}

@SpringBootApplication
@Import(Consumer.class)
public class ProducerApplication {

    public static void main(String[] args) {
        SpringApplication.run(ProducerApplication.class, args);
    }

}

@SpringBootTest(classes = ProducerApplication.class)
@RunWith(SpringJUnit4ClassRunner.class)
public class ConsumerTest {

    @Autowired
    private Consumer consumer;

    @Test
    public void consume() {
        consumer.consume("CONSUME");
    }
}

2.2 implements ImportSelector

实现ImportSelector接口，返回值是导入到容器中的组件全类名。
示例：

public class ConsumerImportSelector implements ImportSelector {
    @Override
    public String[] selectImports(AnnotationMetadata annotationMetadata) {
        return new String[]{"com.zhao.service.Consumer"};
    }
}

@SpringBootApplication
@Import(ConsumerImportSelector.class)
public class ProducerApplication {

    public static void main(String[] args) {
        SpringApplication.run(ProducerApplication.class, args);
    }

}

2.3 implements ImportBeanDefinitionRegistrar

实现ImportBeanDefinitionRegistrar接口，在方法内进行bean注册。
示例：

public class ConsumerRegistrar implements ImportBeanDefinitionRegistrar {

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        //定义bean
        RootBeanDefinition rootBeanDefinition = new RootBeanDefinition(Consumer.class);
        //注册bean
        registry.registerBeanDefinition("consumer", rootBeanDefinition);
    }
}

@SpringBootApplication
@Import(ConsumerRegistrar.class)
public class ProducerApplication {

    public static void main(String[] args) {
        SpringApplication.run(ProducerApplication.class, args);
    }

}

3 扩展

@EnableFeignClients注解