Dubbo源碼分析之ServiceBean的初始化（一）

一、概述

spring容器啓動dubbo provider服務時，會根據spring.xml的文件配置實例化spring context以及初始化bean，DubboNamespaceHandler註冊DubboBeanDefinitionParser解析xml，實例化有關dubbo的相關bean。當初始化服務提供者ServiceBean時，調用afterPropertiesSet方法時，會打開註冊器registry連接，export服務提供者信息。

二、provider service容器啓動

1.provider.xml的解析

<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:dubbo="http://dubbo.apache.org/schema/dubbo"
       xmlns="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
       http://dubbo.apache.org/schema/dubbo http://dubbo.apache.org/schema/dubbo/dubbo.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
    <context:property-placeholder/>

    <dubbo:application name="demo-provider"/>

    <dubbo:registry address="zookeeper://${zookeeper.address:127.0.0.1}:2181"/>

    <dubbo:protocol name="dubbo" port="20880" dispatcher="all" threadpool="cached" threads="2"/>

    <bean id="demoService" class="org.apache.dubbo.samples.basic.impl.DemoServiceImpl"/>

    <dubbo:service interface="org.apache.dubbo.samples.basic.api.DemoService" ref="demoService"/>

</beans>

spring提供工廠模式的xml的解析spi，實現第三方擴展。通過自定義xsd約束文件，以及實現NameSpaceHandler和BeanDefinitionParser接口解析xml文件，實例化bean。

在classpath下找到dubbo.xsd以及spring.handlers和spring.schemas文件

spring.schemas配置文件如下，provider.xml解析時，會更加beans上的命名域找到META-INF下的dubbo.xsd文件。

http\://dubbo.apache.org/schema/dubbo/dubbo.xsd=META-INF/dubbo.xsd
http\://code.alibabatech.com/schema/dubbo/dubbo.xsd=META-INF/compat/dubbo.xsd

 spring.handlers的配置文件如下，根據dubbo名找到DubboNamespaceHandler類解析

http\://dubbo.apache.org/schema/dubbo=org.apache.dubbo.config.spring.schema.DubboNamespaceHandler
http\://code.alibabatech.com/schema/dubbo=org.apache.dubbo.config.spring.schema.DubboNamespaceHandler

DubboNamespaceHandler則會註冊DubboBeanDefinitionParser解析相關的elementName。

public class DubboNamespaceHandler extends NamespaceHandlerSupport {
    @Override
    public void init() {
        registerBeanDefinitionParser("application", new DubboBeanDefinitionParser(ApplicationConfig.class, true));
        registerBeanDefinitionParser("module", new DubboBeanDefinitionParser(ModuleConfig.class, true));
        registerBeanDefinitionParser("registry", new DubboBeanDefinitionParser(RegistryConfig.class, true));
        registerBeanDefinitionParser("config-center", new DubboBeanDefinitionParser(ConfigCenterBean.class, true));
        registerBeanDefinitionParser("metadata-report", new DubboBeanDefinitionParser(MetadataReportConfig.class, true));
        registerBeanDefinitionParser("monitor", new DubboBeanDefinitionParser(MonitorConfig.class, true));
        registerBeanDefinitionParser("metrics", new DubboBeanDefinitionParser(MetricsConfig.class, true));
        registerBeanDefinitionParser("provider", new DubboBeanDefinitionParser(ProviderConfig.class, true));
        registerBeanDefinitionParser("consumer", new DubboBeanDefinitionParser(ConsumerConfig.class, true));
        registerBeanDefinitionParser("protocol", new DubboBeanDefinitionParser(ProtocolConfig.class, true));
        registerBeanDefinitionParser("service", new DubboBeanDefinitionParser(ServiceBean.class, true));
        registerBeanDefinitionParser("reference", new DubboBeanDefinitionParser(ReferenceBean.class, false));
        registerBeanDefinitionParser("annotation", new AnnotationBeanDefinitionParser());
    }
}

下面是DubboBeanDefinitionParser類parse的主要邏輯，因爲是把所有的elementName寫在一起，通過一個方法解析，所有中間有很多elementName以及Attribute值得判斷。

public class DubboBeanDefinitionParser implements BeanDefinitionParser {

    private final Class<?> beanClass;
    private final boolean required;

    public DubboBeanDefinitionParser(Class<?> beanClass, boolean required) {
        this.beanClass = beanClass;
        this.required = required;
    }

    @SuppressWarnings("unchecked")
    private static BeanDefinition parse(Element element, ParserContext parserContext, Class<?> beanClass, boolean required) {
        RootBeanDefinition beanDefinition = new RootBeanDefinition();
        beanDefinition.setBeanClass(beanClass);
        beanDefinition.setLazyInit(false);
        String id = element.getAttribute("id");
        if (StringUtils.isEmpty(id) && required) {
            String generatedBeanName = element.getAttribute("name");
            if (StringUtils.isEmpty(generatedBeanName)) {
                if (ProtocolConfig.class.equals(beanClass)) {
                    generatedBeanName = "dubbo";
                } else {
                    generatedBeanName = element.getAttribute("interface");
                }
            }
            if (StringUtils.isEmpty(generatedBeanName)) {
                generatedBeanName = beanClass.getName();
            }
            id = generatedBeanName;
            int counter = 2;
            while (parserContext.getRegistry().containsBeanDefinition(id)) {
                id = generatedBeanName + (counter++);
            }
        }
        if (id != null && id.length() > 0) {
            if (parserContext.getRegistry().containsBeanDefinition(id)) {
                throw new IllegalStateException("Duplicate spring bean id " + id);
            }
            parserContext.getRegistry().registerBeanDefinition(id, beanDefinition);
            beanDefinition.getPropertyValues().addPropertyValue("id", id);
        }
        if (ProtocolConfig.class.equals(beanClass)) {
            for (String name : parserContext.getRegistry().getBeanDefinitionNames()) {
                BeanDefinition definition = parserContext.getRegistry().getBeanDefinition(name);
                PropertyValue property = definition.getPropertyValues().getPropertyValue("protocol");
                if (property != null) {
                    Object value = property.getValue();
                    if (value instanceof ProtocolConfig && id.equals(((ProtocolConfig) value).getName())) {
                        definition.getPropertyValues().addPropertyValue("protocol", new RuntimeBeanReference(id));
                    }
                }
            }
        } else if (ServiceBean.class.equals(beanClass)) {
            String className = element.getAttribute("class");
            if (className != null && className.length() > 0) {
                RootBeanDefinition classDefinition = new RootBeanDefinition();
                classDefinition.setBeanClass(ReflectUtils.forName(className));
                classDefinition.setLazyInit(false);
                parseProperties(element.getChildNodes(), classDefinition);
                beanDefinition.getPropertyValues().addPropertyValue("ref", new BeanDefinitionHolder(classDefinition, id + "Impl"));
            }
        } else if (ProviderConfig.class.equals(beanClass)) {
            parseNested(element, parserContext, ServiceBean.class, true, "service", "provider", id, beanDefinition);
        } else if (ConsumerConfig.class.equals(beanClass)) {
            parseNested(element, parserContext, ReferenceBean.class, false, "reference", "consumer", id, beanDefinition);
        }
        Set<String> props = new HashSet<>();
        ManagedMap parameters = null;
        for (Method setter : beanClass.getMethods()) {
            String name = setter.getName();
            if (name.length() > 3 && name.startsWith("set")
                    && Modifier.isPublic(setter.getModifiers())
                    && setter.getParameterTypes().length == 1) {
                Class<?> type = setter.getParameterTypes()[0];
                String beanProperty = name.substring(3, 4).toLowerCase() + name.substring(4);
                String property = StringUtils.camelToSplitName(beanProperty, "-");
                props.add(property);
                // check the setter/getter whether match
                Method getter = null;
                try {
                    getter = beanClass.getMethod("get" + name.substring(3), new Class<?>[0]);
                } catch (NoSuchMethodException e) {
                    try {
                        getter = beanClass.getMethod("is" + name.substring(3), new Class<?>[0]);
                    } catch (NoSuchMethodException e2) {
                        // ignore, there is no need any log here since some class implement the interface: EnvironmentAware,
                        // ApplicationAware, etc. They only have setter method, otherwise will cause the error log during application start up.
                    }
                }
                if (getter == null
                        || !Modifier.isPublic(getter.getModifiers())
                        || !type.equals(getter.getReturnType())) {
                    continue;
                }
                if ("parameters".equals(property)) {
                    parameters = parseParameters(element.getChildNodes(), beanDefinition);
                } else if ("methods".equals(property)) {
                    parseMethods(id, element.getChildNodes(), beanDefinition, parserContext);
                } else if ("arguments".equals(property)) {
                    parseArguments(id, element.getChildNodes(), beanDefinition, parserContext);
                } else {
                    String value = element.getAttribute(property);
                    if (value != null) {
                        value = value.trim();
                        if (value.length() > 0) {
                            if ("registry".equals(property) && RegistryConfig.NO_AVAILABLE.equalsIgnoreCase(value)) {
                                RegistryConfig registryConfig = new RegistryConfig();
                                registryConfig.setAddress(RegistryConfig.NO_AVAILABLE);
                                beanDefinition.getPropertyValues().addPropertyValue(beanProperty, registryConfig);
                            } else if ("provider".equals(property) || "registry".equals(property) || ("protocol".equals(property) && ServiceBean.class.equals(beanClass))) {
                                /**
                                 * For 'provider' 'protocol' 'registry', keep literal value (should be id/name) and set the value to 'registryIds' 'providerIds' protocolIds'
                                 * The following process should make sure each id refers to the corresponding instance, here's how to find the instance for different use cases:
                                 * 1. Spring, check existing bean by id, see{@link ServiceBean#afterPropertiesSet()}; then try to use id to find configs defined in remote Config Center
                                 * 2. API, directly use id to find configs defined in remote Config Center; if all config instances are defined locally, please use {@link org.apache.dubbo.config.ServiceConfig#setRegistries(List)}
                                 */
                                beanDefinition.getPropertyValues().addPropertyValue(beanProperty + "Ids", value);
                            } else {
                                Object reference;
                                if (isPrimitive(type)) {
                                    if ("async".equals(property) && "false".equals(value)
                                            || "timeout".equals(property) && "0".equals(value)
                                            || "delay".equals(property) && "0".equals(value)
                                            || "version".equals(property) && "0.0.0".equals(value)
                                            || "stat".equals(property) && "-1".equals(value)
                                            || "reliable".equals(property) && "false".equals(value)) {
                                        // backward compatibility for the default value in old version's xsd
                                        value = null;
                                    }
                                    reference = value;
                                } else if ("onreturn".equals(property)) {
                                    int index = value.lastIndexOf(".");
                                    String returnRef = value.substring(0, index);
                                    String returnMethod = value.substring(index + 1);
                                    reference = new RuntimeBeanReference(returnRef);
                                    beanDefinition.getPropertyValues().addPropertyValue("onreturnMethod", returnMethod);
                                } else if ("onthrow".equals(property)) {
                                    int index = value.lastIndexOf(".");
                                    String throwRef = value.substring(0, index);
                                    String throwMethod = value.substring(index + 1);
                                    reference = new RuntimeBeanReference(throwRef);
                                    beanDefinition.getPropertyValues().addPropertyValue("onthrowMethod", throwMethod);
                                } else if ("oninvoke".equals(property)) {
                                    int index = value.lastIndexOf(".");
                                    String invokeRef = value.substring(0, index);
                                    String invokeRefMethod = value.substring(index + 1);
                                    reference = new RuntimeBeanReference(invokeRef);
                                    beanDefinition.getPropertyValues().addPropertyValue("oninvokeMethod", invokeRefMethod);
                                } else {
                                    if ("ref".equals(property) && parserContext.getRegistry().containsBeanDefinition(value)) {
                                        BeanDefinition refBean = parserContext.getRegistry().getBeanDefinition(value);
                                        if (!refBean.isSingleton()) {
                                            throw new IllegalStateException("The exported service ref " + value + " must be singleton! Please set the " + value + " bean scope to singleton, eg: <bean id=\"" + value + "\" scope=\"singleton\" ...>");
                                        }
                                    }
                                    reference = new RuntimeBeanReference(value);
                                }
                                beanDefinition.getPropertyValues().addPropertyValue(beanProperty, reference);
                            }
                        }
                    }
                }
            }
        }
        NamedNodeMap attributes = element.getAttributes();
        int len = attributes.getLength();
        for (int i = 0; i < len; i++) {
            Node node = attributes.item(i);
            String name = node.getLocalName();
            if (!props.contains(name)) {
                if (parameters == null) {
                    parameters = new ManagedMap();
                }
                String value = node.getNodeValue();
                parameters.put(name, new TypedStringValue(value, String.class));
            }
        }
        if (parameters != null) {
            beanDefinition.getPropertyValues().addPropertyValue("parameters", parameters);
        }
        return beanDefinition;
    }
}

<dubbo:application >會被解析成ApplicationConfig實體類。

<dubbo:registry >會被解析成RegistryConfig實體類。

<dubbo:protocol >會被解析成ProtocolConfig實體類。

<dubbo:service >會被解析成ServiceBean實體類。

ServiceBean及服務接口提供者，dubbo服務註冊的主要邏輯在bean的初始化afterPropertiesSet方法中調用。

public void afterPropertiesSet() throws Exception {
        // ingore codes
        if (!supportedApplicationListener) {
            export();
        }
    }

跟蹤代碼調用父類ServiceConfig的export方法以及發佈Export事件

public void export() {
        super.export();
        // Publish ServiceBeanExportedEvent
        publishExportEvent();
    }

這是一個同步方法，線程安全，首先會 checkAndUpdateSubConfigs

 public synchronized void export() {
        checkAndUpdateSubConfigs();

        if (!shouldExport()) {
            return;
        }

        if (shouldDelay()) {
            DELAY_EXPORT_EXECUTOR.schedule(this::doExport, getDelay(), TimeUnit.MILLISECONDS);
        } else {
            doExport();
        }
    }

協議不是injvm,進行checkRegistry

public void checkAndUpdateSubConfigs() {
        // Use default configs defined explicitly on global configs
        completeCompoundConfigs();
        // Config Center should always being started first.
        startConfigCenter();
        checkDefault();
        checkProtocol();
        checkApplication();
        // if protocol is not injvm checkRegistry
        if (!isOnlyInJvm()) {
            checkRegistry();
        }
	// ingore codes
  }

  下面這個方法會檢查<dubbo:registry>配置是否存在，並將它解析成RegistryConfig，我們已經配置好了，協議爲zookeeper，地址爲127.0.0.1:2181。跟蹤useRegistryForConfigIfNecessary代碼。

protected void checkRegistry() {
    loadRegistriesFromBackwardConfig();

    convertRegistryIdsToRegistries();

    for (RegistryConfig registryConfig : registries) {
        if (!registryConfig.isValid()) {
            throw new IllegalStateException("No registry config found or it's not a valid config! " +
                    "The registry config is: " + registryConfig);
        }
    }

    useRegistryForConfigIfNecessary();
}

出於兼容性目的，如果註冊表協議是zookeeper並且沒有顯式指定配置中心，則使用registry作爲默認配置中心。

private void useRegistryForConfigIfNecessary() {
        registries.stream().filter(RegistryConfig::isZookeeperProtocol).findFirst().ifPresent(rc -> {
            // we use the loading status of DynamicConfiguration to decide whether ConfigCenter has been initiated.
            Environment.getInstance().getDynamicConfiguration().orElseGet(() -> {
                ConfigManager configManager = ConfigManager.getInstance();
                ConfigCenterConfig cc = configManager.getConfigCenter().orElse(new ConfigCenterConfig());
                cc.setProtocol(rc.getProtocol());
                cc.setAddress(rc.getAddress());
                cc.setHighestPriority(false);
                setConfigCenter(cc);
                startConfigCenter();
                return null;
            });
        });
    }

跟蹤startConfigCenter代碼，發現它會prepareEnvironment

void startConfigCenter() {
        if (configCenter == null) {
            ConfigManager.getInstance().getConfigCenter().ifPresent(cc -> this.configCenter = cc);
        }

        if (this.configCenter != null) {
            // TODO there may have duplicate refresh
            this.configCenter.refresh();
            prepareEnvironment();
        }
        ConfigManager.getInstance().refreshAll();
    }

查看prepareEnvironment方法，調用 getDynamicConfiguration方法

private void prepareEnvironment() {
        if (configCenter.isValid()) {
            if (!configCenter.checkOrUpdateInited()) {
                return;
            }
            DynamicConfiguration dynamicConfiguration = getDynamicConfiguration(configCenter.toUrl());
          }
	  // ingore codes
}

這裏使用的是Dubbo的ExtensionLoader spi，發現它支持多種註冊服務器的動態配置，並根據url的協議protocol（此處爲zookeeper）獲取對應的DynamicConfigurationFactory的實現類（此處是ZookeeperDynamicConfigurationFactory）。

然後ZookeeperDynamicConfigurationFactory創建ZookeeperDynamicConfiguration

protected DynamicConfiguration createDynamicConfiguration(URL url) {
        return new ZookeeperDynamicConfiguration(url, zookeeperTransporter);
    }

ZookeeperDynamicConfiguration調用zookeeperTransporter創建zookeeper客戶端並進行session 連接

ZookeeperDynamicConfiguration(URL url, ZookeeperTransporter zookeeperTransporter) {
        this.url = url;
        rootPath = PATH_SEPARATOR + url.getParameter(CONFIG_NAMESPACE_KEY, DEFAULT_GROUP) + "/config";

        initializedLatch = new CountDownLatch(1);
        this.cacheListener = new CacheListener(rootPath, initializedLatch);
        this.executor = Executors.newFixedThreadPool(1, new NamedThreadFactory(this.getClass().getSimpleName(), true));

        zkClient = zookeeperTransporter.connect(url);
        zkClient.addDataListener(rootPath, cacheListener, executor);
        try {
            // Wait for connection
            this.initializedLatch.await();
        } catch (InterruptedException e) {
            logger.warn("Failed to build local cache for config center (zookeeper)." + url);
        }
    }