@Import[快速给容器中导入一个组件]
@Import(要导入到容器中的组件)；容器中就会自动注册这个组件，id默认是全类名

• @Import 注解 其内部是一个 Class 数组

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

• 新建一个Bean Color

public class Color {
}

• 使用@Import 注解快速导入

@Conditional({WindowsCondition.class})
@Import(Color.class)
@Configuration
public class MainConfig2 {

    @Scope("singleton")
    @Lazy
    //@Scope("prototype")
    @Bean("person")
    public Person person(){
        return new Person("zhangsan",22);
    }
    @Conditional(LinuxCondition.class)
    @Bean("linux")
    public Person person01(){
        return new Person("linus",10);
    }

    @Conditional(WindowsCondition.class)
    @Bean("windows")
    public Person person02(){
        return new Person("bill",30);
    }
}

• 同时导入多个bean

@Conditional({WindowsCondition.class})
@Import({Color.class, Red.class})
@Configuration
public class MainConfig2 {

    @Scope("singleton")
    @Lazy
    //@Scope("prototype")
    @Bean("person")
    public Person person(){
        return new Person("zhangsan",22);
    }
    ......
}

@ImportSelector:返回需要导入的组件的全类名数组

• 实现 ImportSelector 接口

public class MyImportSelector implements ImportSelector {
    /**
     *
     * @param importingClassMetadata  当前标注@Import注解的类的所有注解信息
     * @return  返回值，就是到导入到容器中的组件全类名
     */
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {

        //方法不要返回null值
        return new String[]{"com.spring.annotation.bean.Bule","com.spring.annotation.bean.Yellow"};
    }
}

• 单元测试

@Test
    public void testImport(){
        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfig2.class);
        String[] beanDefinitionNames = applicationContext.getBeanDefinitionNames();
        for (String beanDefinitionName : beanDefinitionNames) {
            System.out.println(beanDefinitionName);
        }
    }

• 测试结果

org.springframework.context.annotation.internalConfigurationAnnotationProcessor
org.springframework.context.annotation.internalAutowiredAnnotationProcessor
org.springframework.context.annotation.internalRequiredAnnotationProcessor
org.springframework.context.annotation.internalCommonAnnotationProcessor
org.springframework.context.event.internalEventListenerProcessor
org.springframework.context.event.internalEventListenerFactory
mainConfig2
com.spring.annotation.bean.Color
com.spring.annotation.bean.Bule
com.spring.annotation.bean.Yellow
person
windows 

注意：@Import 注入bean的id 是全类名

ImportBeanDefinitionRegistrar: 手动注册bean到容器中

• 实现ImportBeanDefinitionRegistrar接口

/**
 *  ImportBeanDefinitionRegistrar: 手动注册bean到容器中
 */
public class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {
    /**
     *
     * @param annotationMetadata       当前类的注解信息
     * @param beanDefinitionRegistry   BeanDefinition注册类
     *
     * BeanDefinitionRegistry.registerBeanDefinition手工注册进来
     */
    @Override
    public void registerBeanDefinitions(AnnotationMetadata annotationMetadata,
                                        BeanDefinitionRegistry beanDefinitionRegistry) {

        boolean definition = beanDefinitionRegistry.containsBeanDefinition("com.atguigu.bean.Red");
        boolean definition2 = beanDefinitionRegistry.containsBeanDefinition("com.atguigu.bean.Blue");
        if(definition && definition2){
            //指定Bean定义信息；（Bean的类型，Bean。。。）
            RootBeanDefinition beanDefinition = new RootBeanDefinition(RainBow.class);
            //注册一个Bean，指定bean名
            beanDefinitionRegistry.registerBeanDefinition("rainBow", beanDefinition);
        }
    }
}

• 在@Import注解中使用 中使用

//类中组件统一设置。满足当前条件，这个类中配置的所有bean注册才能生效；
@Conditional({WindowsCondition.class})
@Import({Color.class, MyImportSelector.class, MyImportBeanDefinitionRegistrar.class})
@Configuration
public class MainConfig2 {

    @Scope("singleton")
    @Lazy
    //@Scope("prototype")
    @Bean("person")
    public Person person(){

        return new Person("zhangsan",22);
    }

    @Conditional(LinuxCondition.class)
    @Bean("linux")
    public Person person01(){
        return new Person("linus",10);
    }

    @Conditional(WindowsCondition.class)
    @Bean("windows")
    public Person person02(){
        return new Person("bill",30);
    }
}

• 测试代码

@Test
    public void testImport(){
        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfig2.class);
        String[] beanDefinitionNames = applicationContext.getBeanDefinitionNames();
        for (String beanDefinitionName : beanDefinitionNames) {
            System.out.println(beanDefinitionName);
        }
    }

• 测试结果

Person constructor....
org.springframework.context.annotation.internalConfigurationAnnotationProcessor
org.springframework.context.annotation.internalAutowiredAnnotationProcessor
org.springframework.context.annotation.internalRequiredAnnotationProcessor
org.springframework.context.annotation.internalCommonAnnotationProcessor
org.springframework.context.event.internalEventListenerProcessor
org.springframework.context.event.internalEventListenerFactory
mainConfig2
com.spring.annotation.bean.Color
com.spring.annotation.bean.Bule
com.spring.annotation.bean.Yellow
person
windows

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