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本文主要研究一下dubbo的DubboApplicationContextInitializer

DubboApplicationContextInitializer

dubbo-spring-boot-project-2.7.3/dubbo-spring-boot-compatible/autoconfigure/src/main/java/org/apache/dubbo/spring/boot/context/DubboApplicationContextInitializer.java

public class DubboApplicationContextInitializer implements ApplicationContextInitializer, Ordered {

    @Override
    public void initialize(ConfigurableApplicationContext applicationContext) {
        overrideBeanDefinitions(applicationContext);
    }

    private void overrideBeanDefinitions(ConfigurableApplicationContext applicationContext) {
        applicationContext.addBeanFactoryPostProcessor(new OverrideBeanDefinitionRegistryPostProcessor());
        applicationContext.addBeanFactoryPostProcessor(new DubboConfigBeanDefinitionConflictProcessor());
    }

    @Override
    public int getOrder() {
        return HIGHEST_PRECEDENCE;
    }

}

• DubboApplicationContextInitializer实现了ApplicationContextInitializer, Ordered接口，initialize方法执行overrideBeanDefinitions，它往applicationContext添加了OverrideBeanDefinitionRegistryPostProcessor、DubboConfigBeanDefinitionConflictProcessor；getOrder返回的是HIGHEST_PRECEDENCE

OverrideBeanDefinitionRegistryPostProcessor

dubbo-spring-boot-project-2.7.3/dubbo-spring-boot-compatible/autoconfigure/src/main/java/org/apache/dubbo/spring/boot/beans/factory/config/OverrideBeanDefinitionRegistryPostProcessor.java

public class OverrideBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        registerInfrastructureBean(registry, BEAN_NAME, DubboConfigBeanCustomizer.class);
    }

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
    }
}

• OverrideBeanDefinitionRegistryPostProcessor实现了BeanDefinitionRegistryPostProcessor接口，其postProcessBeanDefinitionRegistry方法调用了BeanRegistrar.registerInfrastructureBean方法注册DubboConfigBeanCustomizer

BeanRegistrar

dubbo-2.7.3-sources.jar!/org/apache/dubbo/config/spring/util/BeanRegistrar.java

public class BeanRegistrar {

    /**
     * Register Infrastructure Bean
     *
     * @param beanDefinitionRegistry {@link BeanDefinitionRegistry}
     * @param beanType               the type of bean
     * @param beanName               the name of bean
     */
    public static void registerInfrastructureBean(BeanDefinitionRegistry beanDefinitionRegistry,
                                                  String beanName,
                                                  Class<?> beanType) {

        if (!beanDefinitionRegistry.containsBeanDefinition(beanName)) {
            RootBeanDefinition beanDefinition = new RootBeanDefinition(beanType);
            beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
            beanDefinitionRegistry.registerBeanDefinition(beanName, beanDefinition);
        }

    }

}

• registerInfrastructureBean在beanDefinitionRegistry没有该beanDefinition的情况下会注册BeanDefinition.ROLE_INFRASTRUCTURE的bean

DubboConfigBeanCustomizer

dubbo-spring-boot-project-2.7.3/dubbo-spring-boot-compatible/autoconfigure/src/main/java/org/apache/dubbo/spring/boot/beans/factory/config/DubboConfigBeanCustomizer.java

@Deprecated
class DubboConfigBeanCustomizer extends NamePropertyDefaultValueDubboConfigBeanCustomizer {

    @Override
    public void customize(String beanName, AbstractConfig dubboConfigBean) {
        boolean valid = isValidPropertyName(dubboConfigBean, beanName);
        if (valid) {
            super.customize(beanName, dubboConfigBean);
        }
    }

    private boolean isValidPropertyName(AbstractConfig dubboConfigBean, String propertyValue) {
        boolean valid = true;
        String propertyName = "name";
        // AbstractConfig.checkName(String,String)
        Method method = findMethod(AbstractConfig.class, "checkName", String.class, String.class);
        try {
            if (!method.isAccessible()) {
                method.setAccessible(true);
            }
            if (BeanUtils.getPropertyDescriptor(dubboConfigBean.getClass(), propertyName) != null) {
                invokeMethod(method, null, propertyName, propertyValue);
            }
        } catch (IllegalStateException e) {
            valid = false;
        }

        return valid;
    }
}

• DubboConfigBeanCustomizer继承了NamePropertyDefaultValueDubboConfigBeanCustomizer，其customize方法会先校验propertyName，在valid的情况下才会执行父类的customize方法

DubboConfigBeanDefinitionConflictProcessor

dubbo-spring-boot-project-2.7.3/dubbo-spring-boot-compatible/autoconfigure/src/main/java/org/apache/dubbo/spring/boot/beans/factory/config/DubboConfigBeanDefinitionConflictProcessor.java

public class DubboConfigBeanDefinitionConflictProcessor implements BeanDefinitionRegistryPostProcessor, Ordered {

    private final Logger logger = LoggerFactory.getLogger(getClass());

    private BeanDefinitionRegistry registry;

    private Environment environment;

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        this.registry = registry;
    }

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        resolveUniqueApplicationConfigBean(registry, beanFactory);
    }

    /**
     * Resolve the unique {@link ApplicationConfig} Bean
     *
     * @param registry    {@link BeanDefinitionRegistry} instance
     * @param beanFactory {@link ConfigurableListableBeanFactory} instance
     * @see EnableDubboConfig
     */
    private void resolveUniqueApplicationConfigBean(BeanDefinitionRegistry registry,
                                                    ConfigurableListableBeanFactory beanFactory) {

        this.environment = beanFactory.getBean(ENVIRONMENT_BEAN_NAME, Environment.class);

        String[] beansNames = beanNamesForTypeIncludingAncestors(beanFactory, ApplicationConfig.class);

        if (beansNames.length < 2) { // If the number of ApplicationConfig beans is less than two, return immediately.
            return;
        }

        // Remove ApplicationConfig Beans that are configured by "dubbo.application.*"
        Stream.of(beansNames)
                .filter(this::isConfiguredApplicationConfigBeanName)
                .forEach(registry::removeBeanDefinition);

        beansNames = beanNamesForTypeIncludingAncestors(beanFactory, ApplicationConfig.class);

        if (beansNames.length > 1) {
            throw new IllegalStateException(String.format("There are more than one instances of %s, whose bean definitions : %s",
                    ApplicationConfig.class.getSimpleName(),
                    Stream.of(beansNames)
                            .map(registry::getBeanDefinition)
                            .collect(Collectors.toList()))
            );
        }
    }

    private boolean isConfiguredApplicationConfigBeanName(String beanName) {
        boolean removed = BeanFactoryUtils.isGeneratedBeanName(beanName)
                // Dubbo ApplicationConfig id as bean name
                || Objects.equals(beanName, environment.getProperty("dubbo.application.id"));

        if (removed) {
            if (logger.isWarnEnabled()) {
                logger.warn("The {} bean [ name : {} ] has been removed!", ApplicationConfig.class.getSimpleName(), beanName);
            }
        }

        return removed;
    }


    @Override
    public int getOrder() {
        return LOWEST_PRECEDENCE;
    }
}

• DubboConfigBeanDefinitionConflictProcessor实现了BeanDefinitionRegistryPostProcessor, Ordered接口；postProcessBeanFactory方法会执行resolveUniqueApplicationConfigBean，校验同一个beanDefinition是否会有多个实例，有的话会抛出IllegalStateException；getOrder返回的是LOWEST_PRECEDENCE

小结

DubboApplicationContextInitializer实现了ApplicationContextInitializer, Ordered接口，initialize方法执行overrideBeanDefinitions，它往applicationContext添加了OverrideBeanDefinitionRegistryPostProcessor、DubboConfigBeanDefinitionConflictProcessor；getOrder返回的是HIGHEST_PRECEDENCE

doc

• DubboApplicationContextInitializer