dubbo的启动过程（一）--BeanDefinition解析

注：源码版本是2.7.4.1

在之前spring学习中，我们知道，spring容器启动的时候，会先生成 BeanDefinition ，这个步骤是在 obtainFreshBeanFactory （我们这里是用注解讲的，所以有点不一样）中。dubbo在项目中，配置了 META-INF/spring.handler ，内容如下：

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的 BeanDefinitionParser 的加载在 DubboNamespaceHandler 类中，通过 DubboBeanDefinitionParser 解析 BeanDefinition 。

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());  
}

具体的解析在 DubboBeanDefinitionParser 的 parse() 中。

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");
    // 没有id，通过name、ProtocolConfig、interface、beanClass赋值给id
    if (StringUtils.isEmpty(id) && required) {
        // 获取名称
        String generatedBeanName = element.getAttribute("name");
        if (StringUtils.isEmpty(generatedBeanName)) {
            // 如果是ProtocolConfig，名称定义为dubbo
            if (ProtocolConfig.class.equals(beanClass)) {
                generatedBeanName = "dubbo";
            } else {
                // 如果不是ProtocolConfig，名称定义为interface的值
                generatedBeanName = element.getAttribute("interface");
            }
        }
        // 如果不是ProtocolConfig且没有interface属性，用类名
        if (StringUtils.isEmpty(generatedBeanName)) {
            generatedBeanName = beanClass.getName();
        }
        id = generatedBeanName;
        int counter = 2;
        while (parserContext.getRegistry().containsBeanDefinition(id)) {
            id = generatedBeanName + (counter++);
        }
    }
    // 注册beanDefinition并增加id的属性值
    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);
    }
    // 给具有protocol属性的赋值
    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)) {
        // 如果有class属性，则创建新的BeanDefinition，并重置ref
        String className = element.getAttribute("class");
        if (StringUtils.isNotEmpty(className)) {
            RootBeanDefinition classDefinition = new RootBeanDefinition();
            classDefinition.setBeanClass(ReflectUtils.forName(className));
            classDefinition.setLazyInit(false);
            // 解析子属性
            parseProperties(element.getChildNodes(), classDefinition);
            // 重置ref
            beanDefinition.getPropertyValues().addPropertyValue("ref", new BeanDefinitionHolder(classDefinition, id + "Impl"));
        }
    } else if (ProviderConfig.class.equals(beanClass)) {
        // 解析Provider子节点的service标签，并给service赋值provider的属性
        parseNested(element, parserContext, ServiceBean.class, true, "service", "provider", id, beanDefinition);
    } else if (ConsumerConfig.class.equals(beanClass)) {
        // 解析Consumer子节点的reference标签，并给reference赋值consumer的属性
        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)) {
                // 解析参数dubbo:parameters属性
                parameters = parseParameters(element.getChildNodes(), beanDefinition);
            } else if ("methods".equals(property)) {
                // 解析方法dubbo:method属性
                parseMethods(id, element.getChildNodes(), beanDefinition, parserContext);
            } else if ("arguments".equals(property)) {
                // 解析方法参数arguments属性
                parseArguments(id, element.getChildNodes(), beanDefinition, parserContext);
            } else {
                String value = element.getAttribute(property);
                if (value != null) {
                    value = value.trim();
                    if (value.length() > 0) {
                        // 点对点的情况
                        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;
}

以上就把ApplicationConfig、ModuleConfig、RegistryConfig等对应的BeanDefinition注册到spring中。