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This article focuses on dubbo's dubbo Component Scan Registrar.

DubboComponentScanRegistrar

dubbo-2.7.3/dubbo-config/dubbo-config-spring/src/main/java/org/apache/dubbo/config/spring/context/annotation/DubboComponentScanRegistrar.java

public class DubboComponentScanRegistrar implements ImportBeanDefinitionRegistrar {

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {

        Set<String> packagesToScan = getPackagesToScan(importingClassMetadata);

        registerServiceAnnotationBeanPostProcessor(packagesToScan, registry);

        registerReferenceAnnotationBeanPostProcessor(registry);

    }

    /**
     * Registers {@link ServiceAnnotationBeanPostProcessor}
     *
     * @param packagesToScan packages to scan without resolving placeholders
     * @param registry       {@link BeanDefinitionRegistry}
     * @since 2.5.8
     */
    private void registerServiceAnnotationBeanPostProcessor(Set<String> packagesToScan, BeanDefinitionRegistry registry) {

        BeanDefinitionBuilder builder = rootBeanDefinition(ServiceAnnotationBeanPostProcessor.class);
        builder.addConstructorArgValue(packagesToScan);
        builder.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        AbstractBeanDefinition beanDefinition = builder.getBeanDefinition();
        BeanDefinitionReaderUtils.registerWithGeneratedName(beanDefinition, registry);

    }

    /**
     * Registers {@link ReferenceAnnotationBeanPostProcessor} into {@link BeanFactory}
     *
     * @param registry {@link BeanDefinitionRegistry}
     */
    private void registerReferenceAnnotationBeanPostProcessor(BeanDefinitionRegistry registry) {

        // Register @Reference Annotation Bean Processor
        BeanRegistrar.registerInfrastructureBean(registry,
                ReferenceAnnotationBeanPostProcessor.BEAN_NAME, ReferenceAnnotationBeanPostProcessor.class);

    }

    private Set<String> getPackagesToScan(AnnotationMetadata metadata) {
        AnnotationAttributes attributes = AnnotationAttributes.fromMap(
                metadata.getAnnotationAttributes(DubboComponentScan.class.getName()));
        String[] basePackages = attributes.getStringArray("basePackages");
        Class<?>[] basePackageClasses = attributes.getClassArray("basePackageClasses");
        String[] value = attributes.getStringArray("value");
        // Appends value array attributes
        Set<String> packagesToScan = new LinkedHashSet<String>(Arrays.asList(value));
        packagesToScan.addAll(Arrays.asList(basePackages));
        for (Class<?> basePackageClass : basePackageClasses) {
            packagesToScan.add(ClassUtils.getPackageName(basePackageClass));
        }
        if (packagesToScan.isEmpty()) {
            return Collections.singleton(ClassUtils.getPackageName(metadata.getClassName()));
        }
        return packagesToScan;
    }

}

• DubboComponentScanRegistrar implements the registerBean Definitions method defined by the ImportBean Definition Registrar interface; it first reads the package to be scanned from Annotation Metadata through the getPackagesToScan method, and then executes the registerService Annotation BeanPostProcessor, registerReference Annotation BeanPostProcessor methods.
• The getPackagesToScan method reads DubboComponentScan annotation information to get the package to scan; the registerService Annotation BeanPostProcessor method registers Service Annotation BeanPostProcessor through BeanDefinitionReaderUtils.registerWithGeneratedName
• The registerReference Annotation BeanPostProcessor method registers the Reference Annotation BeanPostProcessor through the BeanRegistrar. registerInfrastructure Bean

DubboComponentScanRegistrarTest

dubbo-2.7.3/dubbo-config/dubbo-config-spring/src/test/java/org/apache/dubbo/config/spring/context/annotation/DubboComponentScanRegistrarTest.java

public class DubboComponentScanRegistrarTest {

    @BeforeEach
    public void setUp() {
        ConfigManager.getInstance().clear();
    }

    @AfterEach
    public void tearDown() {
        ConfigManager.getInstance().clear();
    }

    @Test
    public void test() {

        AnnotationConfigApplicationContext providerContext = new AnnotationConfigApplicationContext();

        providerContext.register(ProviderConfiguration.class);

        providerContext.refresh();

        DemoService demoService = providerContext.getBean(DemoService.class);

        String value = demoService.sayName("Mercy");

        Assertions.assertEquals("Hello,Mercy", value);

        Class<?> beanClass = AopUtils.getTargetClass(demoService);

        // DemoServiceImpl with @Transactional
        Assertions.assertEquals(DemoServiceImpl.class, beanClass);

        // Test @Transactional is present or not
        Assertions.assertNotNull(findAnnotation(beanClass, Transactional.class));

        AnnotationConfigApplicationContext consumerContext = new AnnotationConfigApplicationContext();

        consumerContext.register(ConsumerConfiguration.class);

        consumerContext.refresh();

        ConsumerConfiguration consumerConfiguration = consumerContext.getBean(ConsumerConfiguration.class);

        demoService = consumerConfiguration.getDemoService();

        value = demoService.sayName("Mercy");

        Assertions.assertEquals("Hello,Mercy", value);

        ConsumerConfiguration.Child child = consumerContext.getBean(ConsumerConfiguration.Child.class);

        // From Child

        demoService = child.getDemoServiceFromChild();

        Assertions.assertNotNull(demoService);

        value = demoService.sayName("Mercy");

        Assertions.assertEquals("Hello,Mercy", value);

        // From Parent

        demoService = child.getDemoServiceFromParent();

        Assertions.assertNotNull(demoService);

        value = demoService.sayName("Mercy");

        Assertions.assertEquals("Hello,Mercy", value);

        // From Ancestor

        demoService = child.getDemoServiceFromAncestor();

        Assertions.assertNotNull(demoService);

        value = demoService.sayName("Mercy");

        Assertions.assertEquals("Hello,Mercy", value);

        providerContext.close();
        consumerContext.close();


    }


}

• DubboComponentScan Registrar Test validates providerContext and consumerContext, respectively.

Summary

• DubboComponentScanRegistrar implements the registerBean Definitions method defined by the ImportBean Definition Registrar interface; it first reads the package to be scanned from Annotation Metadata through the getPackagesToScan method, and then executes the registerService Annotation BeanPostProcessor, registerReference Annotation BeanPostProcessor methods.
• The getPackagesToScan method reads DubboComponentScan annotation information to get the package to scan; the registerService Annotation BeanPostProcessor method registers Service Annotation BeanPostProcessor through BeanDefinitionReaderUtils.registerWithGeneratedName
• The registerReference Annotation BeanPostProcessor method registers the Reference Annotation BeanPostProcessor through the BeanRegistrar. registerInfrastructure Bean

doc

• DubboComponentScanRegistrar