Dubbo Spring 解析

dubbo的spi机制是如何管理dubbo的bean和如何进行扩展的基础。那么dubbo是如何与spring进行集成的呢？先来看一下官方的例子(在我的电脑上需要加上-Djava.net.preferIPv4Stack=true配置才能启动)：

<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"
       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">

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

    <dubbo:registry address="multicast://224.5.6.7:1234"/>

    <dubbo:protocol name="dubbo" port="20880"/>

    <bean id="demoService" class="org.apache.dubbo.demo.provider.DemoServiceImpl"/>

    <dubbo:service interface="org.apache.dubbo.demo.DemoService" ref="demoService"/>

</beans>

可以看到很多都是dubbo自己定义的标签，那么这些标签定义在什么地方呢，beans中最后一行的配置给出了答案。此处通过spring的扩展方案，在META-INF目录下的spring.handlers和spring.schemas两个文件指定了dubbo的xsd文件和DubboNamespaceHandler命名空间解析器实现了扩展。

DubboNamespaceHandler

public class DubboNamespaceHandler extends NamespaceHandlerSupport {
    //检查是否有多个版本
    static {
        Version.checkDuplicate(DubboNamespaceHandler.class);
    }
    //对各个类型的标签解析成对应类型的对象
    @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("monitor", new DubboBeanDefinitionParser(MonitorConfig.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());
    }

}

可以看到除了扫包配置，其他类型都是通过DubboBeanDefinitionParser这个类解析的。

BeanDefinitionParserDelegate

在分析DubboBeanDefinitionParser代码前，有必要简单看一下解析器在Spring中是如何被调用的。

public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
    //找到对应的beans标签中的uri
    String namespaceUri = getNamespaceURI(ele);
    //找到对应的命名空间解析器
    NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
    if (handler == null) {
        error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
        return null;
    }
    //调用解析器解析，注意在DefaultNamespaceHandlerResolver类中已经保证init方法被调用了
    return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}

DubboBeanDefinitionParser

这里仅贴出最重要的一部分代码(其实这个类的代码可以跳过)，看一下是如何对xml标签处理的。

@SuppressWarnings("unchecked")
private static BeanDefinition parse(Element element, ParserContext parserContext, Class<?> beanClass, boolean required) {
    //初始一个RootBeanDefinition
    RootBeanDefinition beanDefinition = new RootBeanDefinition();
    //设置class类型
    beanDefinition.setBeanClass(beanClass);
    //设置非延迟初始化
    beanDefinition.setLazyInit(false);
    //得到xml中定义的id
    String id = element.getAttribute("id");
    if ((id == null || id.length() == 0) && required) {
        //id不存在且必须就去拿name属性
        String generatedBeanName = element.getAttribute("name");
        if (generatedBeanName == null || generatedBeanName.length() == 0) {
            //协议默认为dubbo
            if (ProtocolConfig.class.equals(beanClass)) {
                generatedBeanName = "dubbo";
            } else {
                //默认拿接口全类名
                generatedBeanName = element.getAttribute("interface");
            }
        }
        if (generatedBeanName == null || generatedBeanName.length() == 0) {
            //默认拿接口全类名
            generatedBeanName = beanClass.getName();
        }
        id = generatedBeanName;
        int counter = 2;
        //已经存在生产数字后缀，直到名字不存在
        while (parserContext.getRegistry().containsBeanDefinition(id)) {
            id = generatedBeanName + (counter++);
        }
    }
    if (id != null && id.length() > 0) {
        //id校验唯一
        if (parserContext.getRegistry().containsBeanDefinition(id)) {
            throw new IllegalStateException("Duplicate spring bean id " + id);
        }
        //注册该对象
        parserContext.getRegistry().registerBeanDefinition(id, beanDefinition);
        //添加bean的id属性
        beanDefinition.getPropertyValues().addPropertyValue("id", id);
    }
    //ProtocolConfig类型的特殊处理
    if (ProtocolConfig.class.equals(beanClass)) {
        //遍历当前spring容器内所有的bean的所有解析的属性
        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();
                //如果其他BeanDefinition存在属性值是ProtocolConfig类型并且协议名字一样的那么添加属性
                //这一步实现了类似ServiceConfig有protocol属性的类型可以根据协议名字注入指定协议
                if (value instanceof ProtocolConfig && id.equals(((ProtocolConfig) value).getName())) {
                    definition.getPropertyValues().addPropertyValue("protocol", new RuntimeBeanReference(id));
                }
            }
        }
        //ServiceBean特殊处理
    } else if (ServiceBean.class.equals(beanClass)) {
        //如果<dubbo:service>标签指定了className，那么自动生成该对象，并还是通过ref引用
        String className = element.getAttribute("class");
        if (className != null && className.length() > 0) {
            RootBeanDefinition classDefinition = new RootBeanDefinition();
            classDefinition.setBeanClass(ReflectUtils.forName(className));
            classDefinition.setLazyInit(false);
            //解析属性放到BeanDefinition
            parseProperties(element.getChildNodes(), classDefinition);
            beanDefinition.getPropertyValues().addPropertyValue("ref", new BeanDefinitionHolder(classDefinition, id + "Impl"));
        }
        //ProviderConfig和ConsumerConfig继续扫描内部的dubbo bean
    } 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<String>();
    ManagedMap parameters = null;
    for (Method setter : beanClass.getMethods()) {
        String name = setter.getName();
        //遍历所有的set方法
        if (name.length() > 3 && name.startsWith("set")
                && Modifier.isPublic(setter.getModifiers())
                && setter.getParameterTypes().length == 1) {
            Class<?> type = setter.getParameterTypes()[0];
            //使用-隔开驼峰命名的属性
            String property = StringUtils.camelToSplitName(name.substring(3, 4).toLowerCase() + name.substring(4), "-");
            props.add(property);
            //查找名字对应的get方法
            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) {
                }
            }
            //是否有相应的get方法
            if (getter == null
                    || !Modifier.isPublic(getter.getModifiers())
                    || !type.equals(getter.getReturnType())) {
                continue;
            }
            //有parameters参数，对<dubbo:parameter>解析
            if ("parameters".equals(property)) {
                parameters = parseParameters(element.getChildNodes(), beanDefinition);
                //有parameters参数，对<dubbo:method>解析
            } else if ("methods".equals(property)) {
                parseMethods(id, element.getChildNodes(), beanDefinition, parserContext);
                //argument解析
            } 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) {
                        //不设置注册中心
                        if ("registry".equals(property) && RegistryConfig.NO_AVAILABLE.equalsIgnoreCase(value)) {
                            RegistryConfig registryConfig = new RegistryConfig();
                            registryConfig.setAddress(RegistryConfig.NO_AVAILABLE);
                            beanDefinition.getPropertyValues().addPropertyValue(property, registryConfig);
                            //,隔开的多注册中心
                        } else if ("registry".equals(property) && value.indexOf(',') != -1) {
                            parseMultiRef("registries", value, beanDefinition, parserContext);
                            //多provider提供方配置,隔开
                        } else if ("provider".equals(property) && value.indexOf(',') != -1) {
                            parseMultiRef("providers", value, beanDefinition, parserContext);
                            //多协议配置,隔开
                        } else if ("protocol".equals(property) && value.indexOf(',') != -1) {
                            parseMultiRef("protocols", value, beanDefinition, parserContext);
                        } else {
                            Object reference;
                            if (isPrimitive(type)) {
                                //一些旧属性选项的兼容，可以看到应该都是取消的意思
                                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)) {
                                    value = null;
                                }
                                reference = value;
                            } else if ("protocol".equals(property)
                                    //spi存在该协议，保证可以加载
                                    && ExtensionLoader.getExtensionLoader(Protocol.class).hasExtension(value)
                                    //spring容器内没有该名字对象或者类型不是协议配置
                                    && (!parserContext.getRegistry().containsBeanDefinition(value)
                                    || !ProtocolConfig.class.getName().equals(parserContext.getRegistry().getBeanDefinition(value).getBeanClassName()))) {
                                if ("dubbo:provider".equals(element.getTagName())) {
                                    logger.warn("Recommended replace <dubbo:provider protocol=\"" + value + "\" ... /> to <dubbo:protocol name=\"" + value + "\" ... />");
                                }
                                //这里对应上面protocol属性注入
                                ProtocolConfig protocol = new ProtocolConfig();
                                protocol.setName(value);
                                reference = protocol;
                                //返回回调
                            } else if ("onreturn".equals(property)) {
                                int index = value.lastIndexOf(".");
                                //对象引用
                                String returnRef = value.substring(0, index);
                                //回调方法
                                String returnMethod = value.substring(index + 1);
                                reference = new RuntimeBeanReference(returnRef);
                                beanDefinition.getPropertyValues().addPropertyValue("onreturnMethod", returnMethod);
                                //异?；氐?                            } 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);
                                //调用前回调
                            } 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 {
                                //引用对象
                                if ("ref".equals(property) && parserContext.getRegistry().containsBeanDefinition(value)) {
                                    BeanDefinition refBean = parserContext.getRegistry().getBeanDefinition(value);
                                    //单例
                                    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);
                            }
                            //将解析的属性放入PropertyValues
                            beanDefinition.getPropertyValues().addPropertyValue(property, reference);
                        }
                    }
                }
            }
        }
    }
    //解析参数map
    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;
}

这里的解析大概了解了一下，感觉理解的还不是很到位，不过也不是很重要，对照着官方的使用说明其实一看就七七八八了。

AnnotationBeanDefinitionParser

public class AnnotationBeanDefinitionParser extends AbstractSingleBeanDefinitionParser {

    @Override
    protected void doParse(Element element, ParserContext parserContext, BeanDefinitionBuilder builder) {
        //解析包路径，支持,分隔
        String packageToScan = element.getAttribute("package");
        String[] packagesToScan = trimArrayElements(commaDelimitedListToStringArray(packageToScan));
        //放入ServiceAnnotationBeanPostProcessor的构造入参
        builder.addConstructorArgValue(packagesToScan);
        //bean级别，不是很理解这个的用处
        builder.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);

        //注册ReferenceAnnotationBeanPostProcessor处理Reference注解
        registerReferenceAnnotationBeanPostProcessor(parserContext.getRegistry());

    }
    //没有注定id属性就自动生成
    @Override
    protected boolean shouldGenerateIdAsFallback() {
        return true;
    }

    private void registerReferenceAnnotationBeanPostProcessor(BeanDefinitionRegistry registry) {
        //注册ReferenceAnnotationBeanPostProcessor处理Reference注解
        BeanRegistrar.registerInfrastructureBean(registry,
                ReferenceAnnotationBeanPostProcessor.BEAN_NAME, ReferenceAnnotationBeanPostProcessor.class);

    }
    //注册ServiceAnnotationBeanPostProcessor类型的对象
    @Override
    protected Class<?> getBeanClass(Element element) {
        return ServiceAnnotationBeanPostProcessor.class;
    }

}

这里就是注册了ReferenceAnnotationBeanPostProcessor和ServiceAnnotationBeanPostProcessor两个对象。其中ServiceAnnotationBeanPostProcessor实现了BeanFactoryPostProcessor接口，指定扫包路径扫描Service注解生成ServiceBean。ReferenceAnnotationBeanPostProcessor实现了BeanPostProcessor扫描所有bean的Referenece注解的属性生成ReferenceBean。至于实现的这两个接口是如何工作的，可以查看spring的源码，这是spring提供的一个扩展方式。