Dubbo中xml配置节点解析

Dubbo版本：2.6.2

dubbo是一款和spring结合比较好的框架，按照spring自定义标签规范，使用spring.handlers中定义的NamespaceHandler 来加载dubbo配置文件。

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

DubboNamespaceHandler中注册了各种对dubbo标签的解析器

public class DubboNamespaceHandler extends NamespaceHandlerSupport {
    static {
        //dubbo中大量引用，用于排除jar冲突时的重复引入
        Version.checkDuplicate(DubboNamespaceHandler.class);
    }
    @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());
    }
}

由此可见，对于几乎所有的标签，都由DubboBeanDefinitionParser进行处理，这个类主要作用就是解析xml中的相应标签属性，并最终实例化成BeanDefinition交由spring进行管理

public class DubboBeanDefinitionParser implements BeanDefinitionParser {

    private static final Pattern GROUP_AND_VERION = Pattern.compile("^[\\-.0-9_a-zA-Z]+(\\:[\\-.0-9_a-zA-Z]+)?$");
    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) {
        // 实例化最终需要给Spring装载的BeanDefinition
        RootBeanDefinition beanDefinition = new RootBeanDefinition();
        // 对应的类型由构造方法传入
        beanDefinition.setBeanClass(beanClass);
        // 关闭bean的延迟初始化，使之在容器启动的时候就初始化
        beanDefinition.setLazyInit(false);
        String id = element.getAttribute("id");
        // 从目前看来，只有reference的标签时，required参数才为false
        if ((id == null || id.length() == 0) && required) {
            // 当id为null，需要使用name对id进行补足
            String generatedBeanName = element.getAttribute("name");
            if (generatedBeanName == null || generatedBeanName.length() == 0) {
                if (ProtocolConfig.class.equals(beanClass)) {
                    generatedBeanName = "dubbo";
                } else {
                    generatedBeanName = element.getAttribute("interface");
                }
            }
            if (generatedBeanName == null || generatedBeanName.length() == 0) {
                generatedBeanName = beanClass.getName();
            }
            id = generatedBeanName;
            int counter = 2;
            //有时会有重复的标签，比如定义多个protocol，这时就需要在id后面添加编号
            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);
            }
            //向spring注册BeanDefinition并设置id属性
            parserContext.getRegistry().registerBeanDefinition(id, beanDefinition);
            beanDefinition.getPropertyValues().addPropertyValue("id", id);
        }
        if (ProtocolConfig.class.equals(beanClass)) {
            //将property中定义的protocol替换成该ProtocolConfig的引用
            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)) {
            //dubbo:service标签中，直接指定实现类的class名称，根据全限定名装载BeanDefinition，赋值给ref。
            //替代手动的定义bean并使用ref标签赋值
            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)) {
            // dubbo:provider标签，需要处理标签内的内嵌dubbo:service标签
            parseNested(element, parserContext, ServiceBean.class, true, "service", "provider", id, beanDefinition);
        } else if (ConsumerConfig.class.equals(beanClass)) {
            // dubbo:consumer标签，需要处理标签内的内嵌dubbo:reference标签
            parseNested(element, parserContext, ReferenceBean.class, false, "reference", "consumer", id, beanDefinition);
        }
        Set<String> props = new HashSet<String>();
        ManagedMap parameters = null;
        //遍历bean本身及父类中的所有public方法
        for (Method setter : beanClass.getMethods()) {
            String name = setter.getName();
            //筛选setter方法
            if (name.length() > 3 && name.startsWith("set")
                    && Modifier.isPublic(setter.getModifiers())
                    && setter.getParameterTypes().length == 1) {
                Class<?> type = setter.getParameterTypes()[0];
                String property = StringUtils.camelToSplitName(name.substring(3, 4).toLowerCase() + name.substring(4), "-");
                props.add(property);
                //获取getter方法验证
                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) {
                    }
                }
                if (getter == null
                        || !Modifier.isPublic(getter.getModifiers())
                        || !type.equals(getter.getReturnType())) {
                    continue;
                }
                if ("parameters".equals(property)) {
                    //如果有属性叫parameters，setter方法：setParameters，解析子节点中dubbo:parameter
                    parameters = parseParameters(element.getChildNodes(), beanDefinition);
                } else if ("methods".equals(property)) {
                    //如果有属性叫methods，setter方法：setMethods，解析子节点中dubbo:method
                    parseMethods(id, element.getChildNodes(), beanDefinition, parserContext);
                } else if ("arguments".equals(property)) {
                    //如果有属性叫arguments，setter方法：setArguments，解析子节点中dubbo:argument
                    parseArguments(id, element.getChildNodes(), beanDefinition, parserContext);
                } else {
                    //其他attribute注入BeanDefinition
                    String value = element.getAttribute(property);
                    if (value != null) {
                        value = value.trim();
                        if (value.length() > 0) {
                            if ("registry".equals(property) && RegistryConfig.NO_AVAILABLE.equalsIgnoreCase(value)) {
                                //register="N/A"时，生成默认的注册中心配置
                                RegistryConfig registryConfig = new RegistryConfig();
                                registryConfig.setAddress(RegistryConfig.NO_AVAILABLE);
                                beanDefinition.getPropertyValues().addPropertyValue(property, registryConfig);
                            } else if ("registry".equals(property) && value.indexOf(',') != -1) {
                                //register="regs1,regs2"，多注册中心使用","分割，批量解析注入BeanDefinition
                                parseMultiRef("registries", value, beanDefinition, parserContext);
                            } else if ("provider".equals(property) && value.indexOf(',') != -1) {
                                //provider="provider1,provider2"，多服务提供者使用","分割，批量解析注入BeanDefinition
                                parseMultiRef("providers", value, beanDefinition, parserContext);
                            } else if ("protocol".equals(property) && value.indexOf(',') != -1) {
                                //register="dubbo,rmi"，多协议使用","分割，批量解析注入BeanDefinition
                                parseMultiRef("protocols", value, beanDefinition, parserContext);
                            } else {
                                Object reference;
                                if (isPrimitive(type)) {
                                    //如果type为基础类型，对一些默认值赋值null，适配旧版本
                                    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 ("protocol".equals(property)
                                        && ExtensionLoader.getExtensionLoader(Protocol.class).hasExtension(value)
                                        && (!parserContext.getRegistry().containsBeanDefinition(value)
                                        || !ProtocolConfig.class.getName().equals(parserContext.getRegistry().getBeanDefinition(value).getBeanClassName()))) {
                                    //对protocol进行处理，存在扩展点但是还未加载成BeanDefinition
                                    if ("dubbo:provider".equals(element.getTagName())) {
                                        logger.warn("Recommended replace <dubbo:provider protocol=\"" + value + "\" ... /> to <dubbo:protocol name=\"" + value + "\" ... />");
                                    }
                                    // backward compatibility
                                    ProtocolConfig protocol = new ProtocolConfig();
                                    protocol.setName(value);
                                    reference = protocol;
                                } else if ("onreturn".equals(property)) {
                                    //对onreturn的事件通知进行处理
                                    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)) {
                                    //对onthrow的事件通知进行处理
                                    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)) {
                                    //对oninvoke的事件通知进行处理
                                    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);
                                        //对引用类型的单例验证
                                        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(property, reference);
                            }
                        }
                    }
                }
            }
        }
        //最后对bean中没有对应字段的attributes处理，放入parameters的map里
        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;
    }

    private static boolean isPrimitive(Class<?> cls) {
        return cls.isPrimitive() || cls == Boolean.class || cls == Byte.class
                || cls == Character.class || cls == Short.class || cls == Integer.class
                || cls == Long.class || cls == Float.class || cls == Double.class
                || cls == String.class || cls == Date.class || cls == Class.class;
    }

    //解析用","分隔的多个引用
    @SuppressWarnings("unchecked")
    private static void parseMultiRef(String property, String value, RootBeanDefinition beanDefinition,
                                      ParserContext parserContext) {
        String[] values = value.split("\\s*[,]+\\s*");
        ManagedList list = null;
        for (int i = 0; i < values.length; i++) {
            String v = values[i];
            if (v != null && v.length() > 0) {
                if (list == null) {
                    list = new ManagedList();
                }
                list.add(new RuntimeBeanReference(v));
            }
        }
        beanDefinition.getPropertyValues().addPropertyValue(property, list);
    }

    //递归解析子节点
    private static void parseNested(Element element, ParserContext parserContext, Class<?> beanClass, boolean required, String tag, String property, String ref, BeanDefinition beanDefinition) {
        NodeList nodeList = element.getChildNodes();
        if (nodeList != null && nodeList.getLength() > 0) {
            boolean first = true;
            for (int i = 0; i < nodeList.getLength(); i++) {
                Node node = nodeList.item(i);
                if (node instanceof Element) {
                    if (tag.equals(node.getNodeName())
                            || tag.equals(node.getLocalName())) {
                        if (first) {
                            first = false;
                            String isDefault = element.getAttribute("default");
                            if (isDefault == null || isDefault.length() == 0) {
                                beanDefinition.getPropertyValues().addPropertyValue("default", "false");
                            }
                        }
                        BeanDefinition subDefinition = parse((Element) node, parserContext, beanClass, required);
                        if (subDefinition != null && ref != null && ref.length() > 0) {
                            subDefinition.getPropertyValues().addPropertyValue(property, new RuntimeBeanReference(ref));
                        }
                    }
                }
            }
        }
    }

    private static void parseProperties(NodeList nodeList, RootBeanDefinition beanDefinition) {
        if (nodeList != null && nodeList.getLength() > 0) {
            for (int i = 0; i < nodeList.getLength(); i++) {
                Node node = nodeList.item(i);
                if (node instanceof Element) {
                    if ("property".equals(node.getNodeName())
                            || "property".equals(node.getLocalName())) {
                        String name = ((Element) node).getAttribute("name");
                        if (name != null && name.length() > 0) {
                            String value = ((Element) node).getAttribute("value");
                            String ref = ((Element) node).getAttribute("ref");
                            if (value != null && value.length() > 0) {
                                beanDefinition.getPropertyValues().addPropertyValue(name, value);
                            } else if (ref != null && ref.length() > 0) {
                                beanDefinition.getPropertyValues().addPropertyValue(name, new RuntimeBeanReference(ref));
                            } else {
                                throw new UnsupportedOperationException("Unsupported <property name=\"" + name + "\"> sub tag, Only supported <property name=\"" + name + "\" ref=\"...\" /> or <property name=\"" + name + "\" value=\"...\" />");
                            }
                        }
                    }
                }
            }
        }
    }

    @SuppressWarnings("unchecked")
    private static ManagedMap parseParameters(NodeList nodeList, RootBeanDefinition beanDefinition) {
        if (nodeList != null && nodeList.getLength() > 0) {
            ManagedMap parameters = null;
            for (int i = 0; i < nodeList.getLength(); i++) {
                Node node = nodeList.item(i);
                if (node instanceof Element) {
                    if ("parameter".equals(node.getNodeName())
                            || "parameter".equals(node.getLocalName())) {
                        if (parameters == null) {
                            parameters = new ManagedMap();
                        }
                        String key = ((Element) node).getAttribute("key");
                        String value = ((Element) node).getAttribute("value");
                        boolean hide = "true".equals(((Element) node).getAttribute("hide"));
                        if (hide) {
                            key = Constants.HIDE_KEY_PREFIX + key;
                        }
                        parameters.put(key, new TypedStringValue(value, String.class));
                    }
                }
            }
            return parameters;
        }
        return null;
    }

    @SuppressWarnings("unchecked")
    private static void parseMethods(String id, NodeList nodeList, RootBeanDefinition beanDefinition,
                                     ParserContext parserContext) {
        if (nodeList != null && nodeList.getLength() > 0) {
            ManagedList methods = null;
            for (int i = 0; i < nodeList.getLength(); i++) {
                Node node = nodeList.item(i);
                if (node instanceof Element) {
                    Element element = (Element) node;
                    if ("method".equals(node.getNodeName()) || "method".equals(node.getLocalName())) {
                        String methodName = element.getAttribute("name");
                        if (methodName == null || methodName.length() == 0) {
                            throw new IllegalStateException("<dubbo:method> name attribute == null");
                        }
                        if (methods == null) {
                            methods = new ManagedList();
                        }
                        BeanDefinition methodBeanDefinition = parse(((Element) node),
                                parserContext, MethodConfig.class, false);
                        String name = id + "." + methodName;
                        BeanDefinitionHolder methodBeanDefinitionHolder = new BeanDefinitionHolder(
                                methodBeanDefinition, name);
                        methods.add(methodBeanDefinitionHolder);
                    }
                }
            }
            if (methods != null) {
                beanDefinition.getPropertyValues().addPropertyValue("methods", methods);
            }
        }
    }

    @SuppressWarnings("unchecked")
    private static void parseArguments(String id, NodeList nodeList, RootBeanDefinition beanDefinition,
                                       ParserContext parserContext) {
        if (nodeList != null && nodeList.getLength() > 0) {
            ManagedList arguments = null;
            for (int i = 0; i < nodeList.getLength(); i++) {
                Node node = nodeList.item(i);
                if (node instanceof Element) {
                    Element element = (Element) node;
                    if ("argument".equals(node.getNodeName()) || "argument".equals(node.getLocalName())) {
                        String argumentIndex = element.getAttribute("index");
                        if (arguments == null) {
                            arguments = new ManagedList();
                        }
                        BeanDefinition argumentBeanDefinition = parse(((Element) node),
                                parserContext, ArgumentConfig.class, false);
                        String name = id + "." + argumentIndex;
                        BeanDefinitionHolder argumentBeanDefinitionHolder = new BeanDefinitionHolder(
                                argumentBeanDefinition, name);
                        arguments.add(argumentBeanDefinitionHolder);
                    }
                }
            }
            if (arguments != null) {
                beanDefinition.getPropertyValues().addPropertyValue("arguments", arguments);
            }
        }
    }

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

}

最近学习Dubbo源码，记录下自己的理解，理解还很粗糙，方便今后的回顾与补充。