本文详细介绍了Dubbo在Spring容器中的配置解析流程，包括如何利用DubboNamespaceHandler处理自定义标签，以及如何将XML配置映射到Bean对象。
Dubbo 源码学习笔记（一）Spring容器解析dubbo配置流程
基于dubbo-2.6.0.jar 内的 META-INF/spring.hanlers 配置，Spring 在遇到dubbo命名空间的时，会回调DubboNamespaceHandler。
所有dubbo的标签，都统一用DubboBeanDefinitionParser 进行解析，基于一对一属性的映射，将XML标签解析为Bean对象。
一、启动Spring 容器
// SpringContainer
public void start() {
String configPath = ConfigUtils.getProperty(SPRING_CONFIG);
if (configPath == null || configPath.length() == 0) {
configPath = DEFAULT_SPRING_CONFIG;
}
context = new ClassPathXmlApplicationContext(configPath.split("[,\\s]+"));
context.start();
}二、Spring refresh()->obtainFreshBeanFactory() 获取beanFactory
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
this.refreshBeanFactory(); //创建DefaultListableBeanFactory
ConfigurableListableBeanFactory beanFactory = this.getBeanFactory();
if (this.logger.isDebugEnabled()) {
this.logger.debug("Bean factory for " + this.getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
三、创建一个DefaultListableBeanFactory
protected final void refreshBeanFactory() throws BeansException {
if (this.hasBeanFactory()) {
this.destroyBeans();
this.closeBeanFactory();
}
try {
// 创建DefaultListableBeanFactory
DefaultListableBeanFactory beanFactory = this.createBeanFactory();
beanFactory.setSerializationId(this.getId());
this.customizeBeanFactory(beanFactory);
this.loadBeanDefinitions(beanFactory); //从指定的XML文件加载bean定义
Object var2 = this.beanFactoryMonitor;
synchronized(this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
} catch (IOException var5) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + this.getDisplayName(), var5);
}
}四、loadBeanDefinitions从指定的XML文件加载bean定义
//loadBeanDefinitions:93, AbstractXmlApplicationContext
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
this.initBeanDefinitionReader(beanDefinitionReader);
this.loadBeanDefinitions(beanDefinitionReader);
}五、解析xml信息
//registerBeanDefinitions:94, DefaultBeanDefinitionDocumentReader
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
Element root = doc.getDocumentElement();
doRegisterBeanDefinitions(root);
}
//1 . 执行doRegisterBeanDefinitions:142, DefaultBeanDefinitionDocumentReader
//2 . doRegisterBeanDefinitions:142, DefaultBeanDefinitionDocumentReader
//3 . parseBeanDefinitions:172, DefaultBeanDefinitionDocumentReader
//parseCustomElement:1406, BeanDefinitionParserDelegate
public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
String namespaceUri = getNamespaceURI(ele); //=http://code.alibabatech.com/schema/dubbo
// 从handlerMappings 中获取到DubboNamespaceHandler
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 DubboNamespaceHandler的.parse()方法
return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}5.1、获取xml命名空间的解析器DubboNamespaceHandler
读取所有jar包下的META-INF/spring.handlers 文件，从中加载映射关系，通过namespaceUri得到DubboNamespaceHandler
// resolve:131, DefaultNamespaceHandlerResolver
public NamespaceHandler resolve(String namespaceUri) {
//加载指定的命名空间处理器映射。
Map<String, Object> handlerMappings = getHandlerMappings();
//从map获取命名空间处理器 namespaceUri= http://code.alibabatech.com/schema/dubbo
Object handlerOrClassName = handlerMappings.get(namespaceUri);
if (handlerOrClassName == null) {
return null;
}
//如果缓存的是 NamespaceHandler 的对象直接返回，如果是Class通过反射，获取到NamespaceHandler并init
else if (handlerOrClassName instanceof NamespaceHandler) {
return (NamespaceHandler) handlerOrClassName;
}
else {
//className=com.alibaba.dubbo.config.spring.schema.DubboNamespaceHandler
String className = (String) handlerOrClassName;
try {
Class<?> handlerClass = ClassUtils.forName(className, this.classLoader);
if (!NamespaceHandler.class.isAssignableFrom(handlerClass)) {
throw new FatalBeanException("Class [" + className + "] for namespace [" + namespaceUri +
"] does not implement the [" + NamespaceHandler.class.getName() + "] interface");
}
NamespaceHandler namespaceHandler = (NamespaceHandler) BeanUtils.instantiateClass(handlerClass);
namespaceHandler.init();
handlerMappings.put(namespaceUri, namespaceHandler);
return namespaceHandler;
}
catch (ClassNotFoundException ex) {
throw new FatalBeanException("NamespaceHandler class [" + className + "] for namespace [" +
namespaceUri + "] not found", ex);
}
catch (LinkageError err) {
throw new FatalBeanException("Invalid NamespaceHandler class [" + className + "] for namespace [" +
namespaceUri + "]: problem with handler class file or dependent class", err);
}
}
}5.1.1 、从spring.handlers加载命令空间处理器映射关系
读取所有jar包下的META-INF/spring.handlers 文件，从中加载映射关系，
// DefaultNamespaceHandlerResolver
private Map<String, Object> getHandlerMappings() {
if (this.handlerMappings == null) {
synchronized (this) {
if (this.handlerMappings == null) {
try {
//从META-INF/spring.handlers 中加载映射关系，
Properties mappings =
PropertiesLoaderUtils.loadAllProperties(this.handlerMappingsLocation, this.classLoader);
if (logger.isDebugEnabled()) {
logger.debug("Loaded NamespaceHandler mappings: " + mappings);
}
Map<String, Object> handlerMappings = new ConcurrentHashMap<String, Object>(mappings.size());
CollectionUtils.mergePropertiesIntoMap(mappings, handlerMappings);
this.handlerMappings = handlerMappings;
}
catch (IOException ex) {
throw new IllegalStateException(
"Unable to load NamespaceHandler mappings from location [" + this.handlerMappingsLocation + "]", ex);
}
}
}
}
return this.handlerMappings;
}5.1.2 、DubboNamespaceHandler注册xml标签解析器
Dubbo有10个标签，每个标签会解析到对应的实体上，每个实体中的属性对应标签中的属性
也就是说spring启动过程中，随着Spring在初始化过程中，碰到dubbo命名的标签，如（<dubbo:service>,<dubbo:registry>）等标签，会由DubboNamespaceHandler类处理，具体原理见链接Spring自定义标签
public class DubboNamespaceHandler extends NamespaceHandlerSupport {
static {
Version.checkDuplicate(DubboNamespaceHandler.class);
}
public void init() {
//注册<dubbo:application>标签解析器
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 DubboBeanDefinitionParser(AnnotationBean.class, true));
}
}六、调用DubboBeanDefinitionParser的parse（）
DubboBeanDefinitionParser的parse方法解析步骤
-
初始化RootBeanDefinition
-
获取BeanId
-
将获取到的Bean注册到Spring
-
将xml中配置的信息放到beandefinition的PropertyValues中
@SuppressWarnings("unchecked")
private static BeanDefinition parse(Element element, ParserContext parserContext, Class<?> beanClass, boolean required) {
//Step1 初始化RootBeanDefinition
RootBeanDefinition beanDefinition = new RootBeanDefinition();
beanDefinition.setBeanClass(beanClass);
beanDefinition.setLazyInit(false);
//Step2 获取BeanId
String id = element.getAttribute("id");
//没有BeanId的一些处理步骤，把BeanName做为BeanId
if ((id == null || id.length() == 0) && required) {
String generatedBeanName = element.getAttribute("name");
//BeanName没有设置则按规则生成默认BeanName
if (generatedBeanName == null || generatedBeanName.length() == 0) {
if (ProtocolConfig.class.equals(beanClass)) {
//Protocol特殊处理取名为dubbo
generatedBeanName = "dubbo";
} else {
//其他标签采用interface 属性做为BeanName
generatedBeanName = element.getAttribute("interface");
}
}
//经过如上步骤还为空的话，将className做为BeanName
if (generatedBeanName == null || generatedBeanName.length() == 0) {
generatedBeanName = beanClass.getName();
}
id = generatedBeanName;
int counter = 2;
//判断已经注册表的标签是否已经有同名的
while (parserContext.getRegistry().containsBeanDefinition(id)) {
//有同名的则递增
id = generatedBeanName + (counter++);
}
}
//Step3 将获取到的Bean注册到Spring
if (id != null && id.length() > 0) {
//BeanId 出现重复则抛异常
if (parserContext.getRegistry().containsBeanDefinition(id)) {
throw new IllegalStateException("Duplicate spring bean id " + id);
}
//将xml转换为的Bean注册到Spring的parserContext
parserContext.getRegistry().registerBeanDefinition(id, beanDefinition);
//为已经加载的Bean注册ID
beanDefinition.getPropertyValues().addPropertyValue("id", id);
}
// 不通配置的一些特殊处理
if (ProtocolConfig.class.equals(beanClass)) {
//protocol 特殊处理，增加protocol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();
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)) {
//将provider转换为service
parseNested(element, parserContext, ServiceBean.class, true, "service", "provider", id, beanDefinition);
} else if (ConsumerConfig.class.equals(beanClass)) {
//将consumer转换为reference
parseNested(element, parserContext, ReferenceBean.class, false, "reference", "consumer", id, beanDefinition);
}
//Step4 将xml中配置的信息放到beandefinition的PropertyValues中
Set<String> props = new HashSet<String>();
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) {
//公开的set***方法
Class<?> type = setter.getParameterTypes()[0];
String property = StringUtils.camelToSplitName(name.substring(3, 4).toLowerCase() + name.substring(4), "-");
props.add(property);
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)) {
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(property, registryConfig);
} else if ("registry".equals(property) && value.indexOf(',') != -1) {
parseMultiRef("registries", value, beanDefinition, parserContext);
} else if ("provider".equals(property) && value.indexOf(',') != -1) {
parseMultiRef("providers", value, beanDefinition, parserContext);
} else if ("protocol".equals(property) && value.indexOf(',') != -1) {
parseMultiRef("protocols", value, beanDefinition, parserContext);
} 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 ("protocol".equals(property)
&& ExtensionLoader.getExtensionLoader(Protocol.class).hasExtension(value)
&& (!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 + "\" ... />");
}
// backward compatibility
ProtocolConfig protocol = new ProtocolConfig();
protocol.setName(value);
reference = protocol;
} 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 ("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(property, 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;
}
参考：https://blog.youkuaiyun.com/architect0719/article/details/53066451
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