Importbeandefinitionregistrar registers beans with the container

One 、ImportBeanDefinitionRegistrar

Let's take a look first ImportBeanDefinitionRegistrar What the hell is that? , Click to enter ImportBeanDefinitionRegistrar Source code , As shown below .

public interface ImportBeanDefinitionRegistrar {
    
	default void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry,
			BeanNameGenerator importBeanNameGenerator) {
    
		registerBeanDefinitions(importingClassMetadata, registry);
	}
	default void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
    
	}
}

You can see from the source code ,ImportBeanDefinitionRegistrar It's essentially an interface . stay ImportBeanDefinitionRegistrar Interface , There is one registerBeanDefinitions() Method , adopt registerBeanDefinitions() Method , We can approach Spring Register in container bean example .Spring The official is registering dynamically bean when , Most routines actually use ImportBeanDefinitionRegistrar Interface . all Classes that implement this interface will be ConfigurationClassPostProcessor Handle ,ConfigurationClassPostProcessor Realized BeanFactoryPostProcessor Interface , therefore ImportBeanDefinitionRegistrar Dynamic registration in bean Is prior to relying on it bean The initialization of the , Can also be aop、validator And so on .

Two 、 Usage method

ImportBeanDefinitionRegistrar Need to cooperate with @Import annotation ,@Import Annotation import implements ImportBeanDefinitionRegistrar The class of the interface .

1. ImportBeanDefinitionRegistrar example

since ImportBeanDefinitionRegistrar It's an interface , Let's create a MyImportBeanDefinitionRegistrar class , Realization ImportBeanDefinitionRegistrar Interface , As shown below .

public class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar{
    
    /** * AnnotationMetadata:  Annotation information for the current class  * BeanDefinitionRegistry：BeanDefinition Registration class  *  By calling BeanDefinitionRegistry Interface registerBeanDefinition() Method , You can add all that you need to add to the container bean Pour into the container . */
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
    
        boolean dao1= registry.containsBeanDefinition("com.myImportBeanDefinitionRegistrar.MyDao1");
        boolean dao2= registry.containsBeanDefinition("com.myImportBeanDefinitionRegistrar.MyDao2");
        if (dao2 && dao1){
    
            BeanDefinition beanDefinition = new RootBeanDefinition(MyDao3.class);
            registry.registerBeanDefinition("myDao3", beanDefinition);
        }
    }
}

public class MyDao(1/2/3) {
    
	public void query(){
    
		System.out.println("query MyDao for MyImportSelect");
	}
}

@Import({
    MyDao1.class,MyDao2.class})
@EnableMyImportBeanDefinitionRegistrar
public class AppConfig {
    
}

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(MyImportBeanDefinitionRegistrar.class)
public @interface EnableMyImportBeanDefinitionRegistrar {
    
}

public class MyTest {
    
    public static void main(String[] args) {
    
        AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(AppConfig.class);
        Arrays.stream(ctx.getBeanDefinitionNames()).toList().forEach(System.out::println);
    }
}

adopt EnableMyImportBeanDefinitionRegistrar annotation , We judge according to the conditions , Dynamic introduction MyDao3.class

3、 ... and 、 The same goes for most frameworks

1. openFeign

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(FeignClientsRegistrar.class)
public @interface EnableFeignClients {
    }

FeignClientsRegistrar Realized ImportBeanDefinitionRegistrar Interface 

2. mybatis

@Retention(RetentionPolicy.RUNTIME)
@Target({
    ElementType.TYPE})
@Documented
@Import({
    MapperScannerRegistrar.class})
@Repeatable(MapperScans.class)
public @interface MapperScan {
    }

MapperScannerRegistrar Realized ImportBeanDefinitionRegistrar Interface 

3. There are also implementations importSelector Interface , Injected by returning an array containing the class name