Dubbo与Spring整合分析

Dubbo提供了与spring容器整合的功能，开箱即用。

此文的目的在于以此为例讲述框架与Spring整合的标准流程。

本文暂时先分为两部分，1、服务注册 2、服务消费
先以服务注册为例讲述过程。

使用

定义XML文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:dubbo="http://dubbo.apache.org/schema/dubbo"
       xsi:schemaLocation="http://www.springframework.org/schema/beans        http://www.springframework.org/schema/beans/spring-beans-4.3.xsd        http://dubbo.apache.org/schema/dubbo        http://dubbo.apache.org/schema/dubbo/dubbo.xsd">

    <!-- 提供方应用信息，用于计算依赖关系 -->
    <dubbo:application name="hello-world-app"  />

    <!-- 使用multicast广播注册中心暴露服务地址 -->
    <dubbo:registry address="multicast://224.5.6.7:1234" />

    <!-- 用dubbo协议在20880端口暴露服务 -->
    <dubbo:protocol name="dubbo" port="20880" />

    <!-- 声明需要暴露的服务接口 -->
    <dubbo:service interface="com.example.matrixweb.service.GreetingsService" ref="greetingsService" />

    <!-- 和本地bean一样实现服务 -->
    <bean id="greetingsService" class="com.example.matrixweb.dubbo.provider.GreetingsServiceImpl" />
</beans>

使用Spring容器启动即可

public class SpringApplication {

    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(new String[]{"spring/provider.xml"});
        context.start();
    }
}

原理分析

Spring配置启动的过程主要分为两点：1、配置解析成Spring容器的数据结构。2、通过解析成的数据结构以及描述的对象引用直接的关系构建容器中的引用

Dubbo中所使用的Bean数据的解析

Spring自定义XML中的节点的解析是通过实现NamespaceHandler接口来实现的，并在spring.handlers文件中定义对应名称空间的解析类。

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

Dubbo中使用DubboNamespaceHandler封装了Dubbo中需要使用的Bean的解析逻辑。
DubboNamespaceHandler的代码如下：

public class DubboNamespaceHandler extends NamespaceHandlerSupport implements ConfigurableSourceBeanMetadataElement {

    @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("ssl", new DubboBeanDefinitionParser(SslConfig.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, true));
        registerBeanDefinitionParser("annotation", new AnnotationBeanDefinitionParser());
    }

    /**
     * Override {@link NamespaceHandlerSupport#parse(Element, ParserContext)} method
     *
     * @param element       {@link Element}
     * @param parserContext {@link ParserContext}
     * @return
     * @since 2.7.5
     */
    @Override
    public BeanDefinition parse(Element element, ParserContext parserContext) {
        BeanDefinitionRegistry registry = parserContext.getRegistry();
        registerAnnotationConfigProcessors(registry);
        /**
         * @since 2.7.8
         * issue : https://github.com/apache/dubbo/issues/6275
         */
        registerCommonBeans(registry);
        BeanDefinition beanDefinition = super.parse(element, parserContext);
        setSource(beanDefinition);
        return beanDefinition;
    }

    /**
     * Register the processors for the Spring Annotation-Driven features
     *
     * @param registry {@link BeanDefinitionRegistry}
     * @see AnnotationConfigUtils
     * @since 2.7.5
     */
    private void registerAnnotationConfigProcessors(BeanDefinitionRegistry registry) {
        AnnotationConfigUtils.registerAnnotationConfigProcessors(registry);
    }
}

可以看到所有的标签都是通过DubboBeanDefinitionParser进行解析的。该类实现了Spring的BeanDefinitionParser并实现了parse方法。

该方法的实现主要如下所示：

@Override
public BeanDefinition parse(Element element, ParserContext parserContext) {
    return parse(element, parserContext, beanClass, required);
}

private static RootBeanDefinition parse(Element element, ParserContext parserContext, Class<?> beanClass, boolean required) {
    RootBeanDefinition beanDefinition = new RootBeanDefinition();
    beanDefinition.setBeanClass(beanClass);
    beanDefinition.setLazyInit(false);
    String id = resolveAttribute(element, "id", parserContext);
    if (StringUtils.isEmpty(id) && required) {
        String generatedBeanName = resolveAttribute(element, "name", parserContext);
        if (StringUtils.isEmpty(generatedBeanName)) {
            if (ProtocolConfig.class.equals(beanClass)) {
                generatedBeanName = "dubbo";
            } else {
                generatedBeanName = resolveAttribute(element, "interface", parserContext);
            }
        }
        if (StringUtils.isEmpty(generatedBeanName)) {
            generatedBeanName = beanClass.getName();
        }
        id = generatedBeanName;
        int counter = 2;
        while (parserContext.getRegistry().containsBeanDefinition(id)) {
            id = generatedBeanName + (counter++);
        }
    }
    if (StringUtils.isNotEmpty(id)) {
        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 = resolveAttribute(element, "class", parserContext);
        if (StringUtils.isNotEmpty(className)) {
            RootBeanDefinition classDefinition = new RootBeanDefinition();
            classDefinition.setBeanClass(ReflectUtils.forName(className));
            classDefinition.setLazyInit(false);
            parseProperties(element.getChildNodes(), classDefinition, parserContext);
            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, parserContext);
            } 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 = resolveAttribute(element, property, parserContext);
                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) && AbstractServiceConfig.class.isAssignableFrom(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 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) || ONTHROW.equals(property) || ONINVOKE.equals(property)) {
                                int index = value.lastIndexOf(".");
                                String ref = value.substring(0, index);
                                String method = value.substring(index + 1);
                                reference = new RuntimeBeanReference(ref);
                                beanDefinition.getPropertyValues().addPropertyValue(property + METHOD, method);
                            } 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;
}

所有的标签都是通过该方法解析成BeanDefinition。其中的BeanClass在初始化方法中已经指定。

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("ssl", new DubboBeanDefinitionParser(SslConfig.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, true));
registerBeanDefinitionParser("annotation", new AnnotationBeanDefinitionParser());

最终Spring容器在初始化实例对象时，统一在PostConstract标注的方法中注册到ConfigManager中

/**
 * Add {@link AbstractConfig instance} into {@link ConfigManager}
 * <p>
 * Current method will invoked by Spring or Java EE container automatically, or should be triggered manually.
 *
 * @see ConfigManager#addConfig(AbstractConfig)
 * @since 2.7.5
 */
@PostConstruct
public void addIntoConfigManager() {
    ApplicationModel.getConfigManager().addConfig(this);
}