1. Overall architecture

Note: This article is based on dubo2.7.5, in which service exposure is not a feature of ServiceBean.

1.1 Startup Classes and Configurations

package com.zyz;

import org.apache.dubbo.config.spring.context.annotation.EnableDubbo;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;

public class Application {
    public static void main(String[] args) throws Exception {
        AnnotationConfigApplicationContext context =
                new AnnotationConfigApplicationContext(ProviderConfiguration.class);
        context.start();
        System.in.read();
    }

    @Configuration
    @EnableDubbo(scanBasePackages = "org.apache.dubbo.demo.provider")
    @PropertySource("classpath:/spring/dubbo-provider.properties")
    static class ProviderConfiguration {

    }
}


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2. Source code analysis

2.1 EnableDubbo annotations

Start with the annotation, which scans the classes under the specified package, the @service and @Reference annotations, and processes them.

This annotation contains two important annotations @enableDubboConfig and @DubboComponentScan. One is to convert properties in the configuration file to beans and assign values, and the other is to scan @service and @Reference annotations.

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
@EnableDubboConfig
@DubboComponentScan
@EnableDubboLifecycle
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2.1.1 @ EnableDubboConfig annotation

Enter the annotations, found @ Import DubboConfigConfigurationRegistrar class

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
@Import(DubboConfigConfigurationRegistrar.class)
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2.1.2 DubboConfigConfigurationRegistrar class

As is customary in Spring, a class annotated with @import performs a registration method to register itself as a Bean. So let’s look at the registration method for this class.

@Override public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { AnnotationAttributes attributes = AnnotationAttributes.fromMap( importingClassMetadata.getAnnotationAttributes(EnableDubboConfig.class.getName())); boolean multiple = attributes.getBoolean("multiple"); / / a Single binding configuration registerBeans (registry, DubboConfigConfiguration. Single. Class); / / multiple instances binding configuration if (multiple) {/ / Since 2.6.6 https://github.com/apache/dubbo/issues/3193 registerBeans (registry, DubboConfigConfiguration.Multiple.class); } / / registered DubboConfigAliasPostProcessor registerDubboConfigAliasPostProcessor post processor (registry); / / registered NamePropertyDefaultValueDubboConfigBeanCustomizer registerDubboConfigBeanCustomizers (registry); }Copy the code

This is what single binding and multi-instance binding mean:

Single binding:

dubbo.protocol.name=dubbo
dubbo.protocol.port=20880
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Multi-instance binding:

Dubbo. Separate protocols. P1. Id = dubbo1 dubbo. Separate protocols. (p1) name = dubbo dubbo. Separate protocols. (p1) port = 20881 dubbo. Separate protocols. P1. Host = 0.0.0.0  dubbo.protocols.p2.id=dubbo2 dubbo.protocols.p2.name=dubbo dubbo.protocols.p2.port=20882 Dubbo. Separate protocols. P2. Host = 0.0.0.0 dubbo. Separate protocols. P3. Id = dubbo3 dubbo. Separate protocols. P3. Name = dubbo dubbo. Separate protocols. P3. Port = 20883 Dubbo. Separate protocols. P3. Host = 0.0.0.0Copy the code

2.1.3 DubboConfigConfiguration class

The purpose of this class is to bind the configuration information in the configuration file to a specific class.

Protocol is bound to protocolConfig. class, for example.

public class DubboConfigConfiguration {

    /**
     * Single Dubbo {@link AbstractConfig Config} Bean Binding
     */
    @EnableConfigurationBeanBindings({
            @EnableConfigurationBeanBinding(prefix = "dubbo.application", type = ApplicationConfig.class),
            @EnableConfigurationBeanBinding(prefix = "dubbo.module", type = ModuleConfig.class),
            @EnableConfigurationBeanBinding(prefix = "dubbo.registry", type = RegistryConfig.class),
            @EnableConfigurationBeanBinding(prefix = "dubbo.protocol", type = ProtocolConfig.class),
            @EnableConfigurationBeanBinding(prefix = "dubbo.monitor", type = MonitorConfig.class),
            @EnableConfigurationBeanBinding(prefix = "dubbo.provider", type = ProviderConfig.class),
            @EnableConfigurationBeanBinding(prefix = "dubbo.consumer", type = ConsumerConfig.class),
            @EnableConfigurationBeanBinding(prefix = "dubbo.config-center", type = ConfigCenterBean.class),
            @EnableConfigurationBeanBinding(prefix = "dubbo.metadata-report", type = MetadataReportConfig.class),
            @EnableConfigurationBeanBinding(prefix = "dubbo.metrics", type = MetricsConfig.class),
            @EnableConfigurationBeanBinding(prefix = "dubbo.ssl", type = SslConfig.class)
    })
    public static class Single {

    }

    /**
     * Multiple Dubbo {@link AbstractConfig Config} Bean Binding
     */
    @EnableConfigurationBeanBindings({
            @EnableConfigurationBeanBinding(prefix = "dubbo.applications", type = ApplicationConfig.class, multiple = true),
            @EnableConfigurationBeanBinding(prefix = "dubbo.modules", type = ModuleConfig.class, multiple = true),
            @EnableConfigurationBeanBinding(prefix = "dubbo.registries", type = RegistryConfig.class, multiple = true),
            @EnableConfigurationBeanBinding(prefix = "dubbo.protocols", type = ProtocolConfig.class, multiple = true),
            @EnableConfigurationBeanBinding(prefix = "dubbo.monitors", type = MonitorConfig.class, multiple = true),
            @EnableConfigurationBeanBinding(prefix = "dubbo.providers", type = ProviderConfig.class, multiple = true),
            @EnableConfigurationBeanBinding(prefix = "dubbo.consumers", type = ConsumerConfig.class, multiple = true),
            @EnableConfigurationBeanBinding(prefix = "dubbo.config-centers", type = ConfigCenterBean.class, multiple = true),
            @EnableConfigurationBeanBinding(prefix = "dubbo.metadata-reports", type = MetadataReportConfig.class, multiple = true),
            @EnableConfigurationBeanBinding(prefix = "dubbo.metricses", type = MetricsConfig.class, multiple = true)
    })
    public static class Multiple {

    }
}
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2.1.4 @ EnableConfigurationBeanBindings

This annotation is contains all configuration information, note that the annotation @ Import the ConfigurationBeanBindingsRegister class.

2.1.5 ConfigurationBeanBindingsRegister class

Since this is introduced by the @import annotation, look at the class registration method.

@Override public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {// Get attributes in the configuration file (stored with key-value) AnnotationAttributes attributes = AnnotationAttributes.fromMap( importingClassMetadata.getAnnotationAttributes(EnableConfigurationBeanBindings.class.getName())); / / configuration properties, is to dubbo. Registrie these values AnnotationAttributes [] AnnotationAttributes = attributes. GetAnnotationArray (" value "); ConfigurationBeanBindingRegistrar registrar = new ConfigurationBeanBindingRegistrar(); registrar.setEnvironment(environment); AnnotationAttributes Element: annotationAttributes) { registrar.registerConfigurationBeanDefinitions(element, registry); }}Copy the code

2.1.6 registerConfigurationBeanDefinitions () method

This method registers the properties in the configuration file as a bean

protected void registerConfigurationBeanDefinitions(AnnotationAttributes attributes, BeanDefinitionRegistry registry) { String prefix = environment.resolvePlaceholders(attributes.getString("prefix")); Class<? > configClass = attributes.getClass("type"); boolean multiple = attributes.getBoolean("multiple"); boolean ignoreUnknownFields = attributes.getBoolean("ignoreUnknownFields"); boolean ignoreInvalidFields = attributes.getBoolean("ignoreInvalidFields"); registerConfigurationBeans(prefix, configClass, multiple, ignoreUnknownFields, ignoreInvalidFields, registry); }Copy the code

2.1.7 registerConfigurationBeans () method

This method registers the values in the configuration properties as bean-by-bean, but there is no assignment yet. Instead, the assignment is made later by registering an assignment post-processor.

private void registerConfigurationBeans(String prefix, Class<? > configClass, boolean multiple, boolean ignoreUnknownFields, boolean ignoreInvalidFields, BeanDefinitionRegistry registry) { Map<String, Object> configurationProperties = PropertySourcesUtils.getSubProperties(environment.getPropertySources(), environment, prefix); if (CollectionUtils.isEmpty(configurationProperties)) { if (log.isDebugEnabled()) { log.debug("There is no property for binding to configuration class [" + configClass.getName() + "] within prefix [" + prefix + "]"); } return; } // Set<String> beanNames = multiple? resolveMultipleBeanNames(configurationProperties) : singleton(resolveSingleBeanName(configurationProperties, configClass, registry)); // Register as a bean, but do not assign a value. for (String beanName : beanNames) { registerConfigurationBean(beanName, configClass, multiple, ignoreUnknownFields, ignoreInvalidFields, configurationProperties, registry); } / / registered post processor binding bean attribute value registerConfigurationBindingBeanPostProcessor (registry); }Copy the code

2.1.8 ConfigurationBeanBindingPostProcessor class

This is where knowledge of the Spring post-processor is used, first initializing the class via postProcessBeanFactory, and then assigning the previously initialized bean when the Spring container calls the first post-processor.

@Override public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException { // Initialize the bean factory this.beanFactory = beanFactory; / / initialize ConfigurationBeanBinder binder initConfigurationBeanBinder (); initBindConfigurationBeanCustomizers(); }Copy the code

@Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { BeanDefinition beanDefinition = getNullableBeanDefinition(beanName); If (isConfigurationBean(beanDefinition)) {bindConfigurationBean(Bean, beanDefinition); beanDefinition); // After binding, execute setName and getName methods customize(beanName, bean); } return bean; }Copy the code

Dubbo has now converted the properties we configured in the configuration file into Dubbo’s configuration Bean and assigned the values.

Summarize the overall process.

2.2 Obtaining the @Service Process

View the @ DubboComponentScan annotations, found @ Import DubboComponentScanRegistrar class, then the class is @ the class of Service and @ the Reference.

Look at the registration method for this class.

@Override public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {// Get scan package directory, That is, dubo.scan. Base-packages or @enableDubbo (scanBasePackages = "com.zyz.provider. Service ") Set<String> packagesToScan = getPackagesToScan(importingClassMetadata); / / registered ServiceAnnotationBeanPostProcessor post processor, was once the scan to a @ Service annotations and it by its annotation class as a Dubbo Service, For service export registerServiceAnnotationBeanPostProcessor (packagesToScan, registry); / / 2.3 analysis registerReferenceAnnotationBeanPostProcessor (registry); }Copy the code

2.2.1 registerServiceAnnotationBeanPostProcessor () method

This method is mainly the ServiceAnnotationBeanPostProcessor class registration

2.2.2 ServiceAnnotationBeanPostProcessor class

This class is the one registered with the @service annotation.

@Override public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException { // Registering registerBeans DubboBootstrapApplicationListener class (registry, DubboBootstrapApplicationListener. Class); Set<String> resolvedPackagesToScan = resolvePackagesToScan(packagesToScan); if (! Collectionutils. isEmpty(resolvedPackagesToScan) {// Register ServiceBean registerServiceBeans(resolvedPackagesToScan, registry); } else { if (logger.isWarnEnabled()) { logger.warn("packagesToScan is empty , ServiceBean registry will be ignored!" ); }}}Copy the code

2.2.3 registerServiceBeans () method

Private void registerServiceBeans(Set<String> packagesToScan, BeanDefinitionRegistry registry) {// Initialize Dubbo's own scan class, Scanning @ Service annotations DubboClassPathBeanDefinitionScanner scanner = new DubboClassPathBeanDefinitionScanner (registry, environment, resourceLoader); // Initialize BeanNameGenerator BeanNameGenerator = resolveBeanNameGenerator(registry); scanner.setBeanNameGenerator(beanNameGenerator); scanner.addIncludeFilter(new AnnotationTypeFilter(Service.class)); /** * Add the compatibility for legacy Dubbo's @Service * * The issue : https://github.com/apache/dubbo/issues/4330 * @ since 2.7.3 * / scanner. AddIncludeFilter (new AnnotationTypeFilter(com.alibaba.dubbo.config.annotation.Service.class)); For (String packageToScan: packagesToScan) {// Register the class annotated by @service, in this case register Spring's Bean scanner.scan(packageToScan); / / find the Bean in the Spring (registered) above the Set < BeanDefinitionHolder > beanDefinitionHolders = findServiceBeanDefinitionHolders (scanner, packageToScan, registry, beanNameGenerator); if (! CollectionUtils.isEmpty(beanDefinitionHolders)) { for (BeanDefinitionHolder beanDefinitionHolder : BeanDefinitionHolders) {// What is registered here is Dubbo's ServiceBean registerServiceBean(beanDefinitionHolder, Registry, scanner); } if (logger.isInfoEnabled()) { logger.info(beanDefinitionHolders.size() + " annotated Dubbo's @Service Components { " +  beanDefinitionHolders + " } were scanned under package[" + packageToScan + "]"); } } else { if (logger.isWarnEnabled()) { logger.warn("No Spring Bean annotating Dubbo's @Service was found under package[" + packageToScan + "]"); }}}}Copy the code

2.2.4 registerServiceBean () method

private void registerServiceBean(BeanDefinitionHolder beanDefinitionHolder, BeanDefinitionRegistry registry, DubboClassPathBeanDefinitionScanner scanner) {/ / get be @ the Class of Service annotation Class <? > beanClass = resolveClass(beanDefinitionHolder); Annotation Service = findServiceAnnotation(beanClass); / / get @ the attribute values of Service annotations AnnotationAttributes serviceAnnotationAttributes = getAnnotationAttributes (Service, false, false); // Get the interface Class<? > interfaceClass = resolveServiceInterfaceClass(serviceAnnotationAttributes, beanClass); / / get the class name String annotatedServiceBeanName = beanDefinitionHolder. GetBeanName (); AbstractBeanDefinition serviceBeanDefinition = buildServiceBeanDefinition(service, serviceAnnotationAttributes, interfaceClass, annotatedServiceBeanName); // Get ServiceBeanName, Such as: ServiceBean: com. Zyz. DemoService: async String beanName = generateServiceBeanName (serviceAnnotationAttributes, interfaceClass); if (scanner.checkCandidate(beanName, ServiceBeanDefinition)) {/ / registered ServiceBean registry. RegisterBeanDefinition (beanName serviceBeanDefinition); if (logger.isInfoEnabled()) { logger.info("The BeanDefinition[" + serviceBeanDefinition + "] of ServiceBean has been registered with name : " + beanName); } } else { if (logger.isWarnEnabled()) { logger.warn("The Duplicated BeanDefinition[" + serviceBeanDefinition + "] of ServiceBean[ bean name : " + beanName + "] was be found , Did @DubboComponentScan scan to same package in many times?" ); }}}Copy the code

At this point, the analysis is complete, this part of the code is relatively simple, is registered two beans.

2.3 Obtaining @Reference Process

In section 2.2 a registerReferenceAnnotationBeanPostProcessor () method, this method is a registered ReferenceAnnotationBeanPostProcessor this post processor, Classes and methods used to get @Reference annotations and inject properties. The class inherited AbstractAnnotationBeanPostProcessor class again.

2.3.1 AbstractAnnotationBeanPostProcessor

Will call the class first postProcessPropertyValues () method

@Override public PropertyValues postProcessPropertyValues( PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeanCreationException {// Get all injected attributes InjectionMetadata Metadata = findInjectionMetadata(beanName, bean.getClass(), pvs); try { metadata.inject(bean, beanName, pvs); } catch (BeanCreationException ex) { throw ex; } catch (Throwable ex) { throw new BeanCreationException(beanName, "Injection of @" + getAnnotationType().getSimpleName() + " dependencies is failed", ex); } return pvs; }Copy the code

2.3.2 findInjectionMetadata () method

private InjectionMetadata findInjectionMetadata(String beanName, Class<? String cacheKey = (stringutils.hasLength (beanName)? beanName : clazz.getName()); // Quick check on the concurrent map first, with minimal locking. AbstractAnnotationBeanPostProcessor.AnnotatedInjectionMetadata metadata = this.injectionMetadataCache.get(cacheKey); if (InjectionMetadata.needsRefresh(metadata, clazz)) { synchronized (this.injectionMetadataCache) { metadata = this.injectionMetadataCache.get(cacheKey); if (InjectionMetadata.needsRefresh(metadata, clazz)) { if (metadata ! = null) { metadata.clear(pvs); } try {// Build attribute metadata = buildAnnotatedMetadata(clazz); this.injectionMetadataCache.put(cacheKey, metadata); } catch (NoClassDefFoundError err) { throw new IllegalStateException("Failed to introspect object class [" + clazz.getName() + "] for annotation metadata: could not find class that it depends on", err); } } } } return metadata; }Copy the code

2.3.3 buildAnnotatedMetadata () method

private AbstractAnnotationBeanPostProcessor.AnnotatedInjectionMetadata buildAnnotatedMetadata(final Class<? > beanClass) {/ / to get class @ Reference Collection < AbstractAnnotationBeanPostProcessor. AnnotatedFieldElement > fieldElements = findFieldAnnotationMetadata(beanClass); / / get in the way that @ Reference Collection < AbstractAnnotationBeanPostProcessor. AnnotatedMethodElement > methodElements = findAnnotatedMethodMetadata(beanClass); return new AbstractAnnotationBeanPostProcessor.AnnotatedInjectionMetadata(beanClass, fieldElements, methodElements); }Copy the code

2.3.4 inject () method

Return postProcessPropertyValues method, look at this line

metadata.inject(bean, beanName, pvs);
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See above know that returns this object AbstractAnnotationBeanPostProcessor. AnnotatedInjectionMetadata, Here is called AnnotatedInjectionMetadata. Inject traversal method, there are these two properties due to the class

        private final Collection<AbstractAnnotationBeanPostProcessor.AnnotatedFieldElement> fieldElements;

        private final Collection<AbstractAnnotationBeanPostProcessor.AnnotatedMethodElement> methodElements;
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So will traverse the respectively, is called AnnotatedFieldElement. Inject method.

@override protected void inject(Object bean, String beanName, PropertyValues PVS) throws Throwable { > injectedType = field.getType(); InjectedObject = getInjectedObject(Attributes, bean, beanName, injectedType, this); ReflectionUtils.makeAccessible(field); field.set(bean, injectedObject); }Copy the code

2.3.5 getInjectedObject () method

protected Object getInjectedObject(AnnotationAttributes attributes, Object bean, String beanName, Class<? > injectedType, InjectionMetadata.InjectedElement injectedElement) throws Exception { String cacheKey = buildInjectedObjectCacheKey(attributes, bean, beanName, injectedType, injectedElement); InjectedObject = injectedObjectsCache. Get (cacheKey); // Cache does not exist, Initialize if (injectedObject == null) {injectedObject = doGetInjectedBean(Attributes, bean, beanName, injectedType, injectedElement); // Customized inject-object if necessary injectedObjectsCache.putIfAbsent(cacheKey, injectedObject); } return injectedObject; }Copy the code

2.3.6 doGetInjectedBean () method

Here referencedBeanName and referenceBeanName are not easy to understand, I hope they can be optimized in the future.

@Override protected Object doGetInjectedBean(AnnotationAttributes attributes, Object bean, String beanName, Class<? > injectedType, InjectionMetadata. InjectedElement InjectedElement) throws the Exception {/ / generates ServiceBean: com. Zyz. DemoService: the default String  referencedBeanName = buildReferencedBeanName(attributes, injectedType); //@Reference(version=default) com.zyz.DemoService String referenceBeanName = getReferenceBeanName(attributes, injectedType); / / create ReferenceBean ReferenceBean ReferenceBean = buildReferenceBeanIfAbsent (referenceBeanName, attributes, injectedType); // Register the ReferenceBean(referencedBeanName, ReferenceBean, Attributes, injectedType); / / cache cacheInjectedReferenceBean (referenceBean injectedElement); Return getOrCreateProxy(referencedBeanName, referenceBeanName, referenceBean, injectedType); }Copy the code

2.3.7 getOrCreateProxy () method

private Object getOrCreateProxy(String referencedBeanName, String referenceBeanName, ReferenceBean referenceBean, Class<? > serviceInterfaceType) {if (existsServiceBean(referencedBeanName)) { Return newProxyInstance(getClassLoader(), new Class[]{serviceInterfaceType}, wrapInvocationHandler(referenceBeanName, referenceBean)); } else {// We should go to the registry to get the service and create the object. }}Copy the code

2.3.8 referenceBean. The get ()

For this method, the follow-up to optimize, and if can ensure that access to the remote service logic, after DubboLifecycleComponentApplicationListener events, can avoid start DubboBootstrap. The init (), Because DubboBootstrap is initiated after DubboLifecycleComponentApplicationListener.

public synchronized T get() { if (destroyed) { throw new IllegalStateException("The invoker of ReferenceConfig(" + url +  ") has already destroyed!" ); } if (ref == null) {// initialize remote service init(); } return ref; }Copy the code

So far the source code analysis is finished.