Tomcat环境下Spring加载Dubbo过程
1.Tomcat容器加载web.xml
web.xml的加载顺序是: <context-param>-> <listener> -> <filter> -> <servlet>。其中，如果web.xml中出现了相同的元素，则按照在配置文件中出现的先后顺序来加载。
启动WEB项目的时候，容器首先会去读取web.xml配置文件中的两个节点：<context-param> </context-param>和<listener> </listener>
紧接着，容器创建一个ServletContext(application),这个web项目的所有部分都将共享这个上下文。容器以<context-param></context-param>的name作为键，value作为值，将其转化为键值对，存入ServletContext。
容器创建<listener></listener>中的类实例，根据配置的class类路径<listener-class>来创建监听，在监听中会有初始化方法，启动Web应用时，系统调用Listener的该方法 contextInitialized(ServletContextEvent args)
2.当Servlet上下文创建好之后，由容器调用监听类org.springframework.web.context.ContextLoaderListener#contextInitialized(ServletContextEvent event)，该方法调用org.springframework.web.context.ContextLoader#initWebApplicationContext(ServletContext servletContext)
@Override public void contextInitialized(ServletContextEvent event) { initWebApplicationContext(event.getServletContext()); }
3.org.springframework.web.context.ContextLoader#initWebApplicationContext(ServletContext servletContext)，方法中调用本类的configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc)
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) { if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {//判断WebApplicationContext是否启动过 throw new IllegalStateException( "Cannot initialize context because there is already a root application context present - " + "check whether you have multiple ContextLoader* definitions in your web.xml!"); } Log logger = LogFactory.getLog(ContextLoader.class); servletContext.log("Initializing Spring root WebApplicationContext"); if (logger.isInfoEnabled()) { logger.info("Root WebApplicationContext: initialization started"); } long startTime = System.currentTimeMillis(); try { // Store context in local instance variable, to guarantee that // it is available on ServletContext shutdown. if (this.context == null) { this.context = createWebApplicationContext(servletContext);//默认创建一个XmlWebApplicationContext } if (this.context instanceof ConfigurableWebApplicationContext) {//关系见XmlWebApplicationContext类图 ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context; if (!cwac.isActive()) {//应用上下文创建之后处在未激活状态 // The context has not yet been refreshed -> provide services such as // setting the parent context, setting the application context id, etc if (cwac.getParent() == null) { // The context instance was injected without an explicit parent -> // determine parent for root web application context, if any. ApplicationContext parent = loadParentContext(servletContext); cwac.setParent(parent); } configureAndRefreshWebApplicationContext(cwac, servletContext); } } servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context); ClassLoader ccl = Thread.currentThread().getContextClassLoader(); if (ccl == ContextLoader.class.getClassLoader()) { currentContext = this.context; } else if (ccl != null) { currentContextPerThread.put(ccl, this.context); } if (logger.isDebugEnabled()) { logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" + WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]"); } if (logger.isInfoEnabled()) { long elapsedTime = System.currentTimeMillis() - startTime; logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms"); } return this.context; } catch (RuntimeException ex) { logger.error("Context initialization failed", ex); servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex); throw ex; } catch (Error err) { logger.error("Context initialization failed", err); servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err); throw err; } }
附：XmlWebApplicationContext类图
4.org.springframework.web.context.ContextLoader#configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc)
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) { if (ObjectUtils.identityToString(wac).equals(wac.getId())) { // The application context id is still set to its original default value // -> assign a more useful id based on available information String idParam = sc.getInitParameter(CONTEXT_ID_PARAM); if (idParam != null) { wac.setId(idParam); } else { // Generate default id... wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX + ObjectUtils.getDisplayString(sc.getContextPath())); } } wac.setServletContext(sc); String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);//获取web.xml中通过<context-param>设置的name为contextConfigLocation的value值，该值代表配置文件放置位置 if (configLocationParam != null) { wac.setConfigLocation(configLocationParam); } // The wac environment's #initPropertySources will be called in any case when the context // is refreshed; do it eagerly here to ensure servlet property sources are in place for // use in any post-processing or initialization that occurs below prior to #refresh ConfigurableEnvironment env = wac.getEnvironment(); if (env instanceof ConfigurableWebEnvironment) { ((ConfigurableWebEnvironment) env).initPropertySources(sc, null); } customizeContext(sc, wac); wac.refresh();//调用AbstractApplicationContext#refresh() }
5.org.springframework.context.support.AbstractApplicationContext#refresh()，该方法是线程安全的，注意方法里面的obtainFreshBeanFactory()。
@Override public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. prepareRefresh(); // Tell the subclass to refresh the internal bean factory. ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. prepareBeanFactory(beanFactory); try { // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. registerBeanPostProcessors(beanFactory); // Initialize message source for this context. initMessageSource(); // Initialize event multicaster for this context. initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses. onRefresh(); // Check for listener beans and register them. registerListeners(); // Instantiate all remaining (non-lazy-init) singletons. finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event. finishRefresh(); } catch (BeansException ex) { if (logger.isWarnEnabled()) { logger.warn("Exception encountered during context initialization - " + "cancelling refresh attempt: " + ex); } // Destroy already created singletons to avoid dangling resources. destroyBeans(); // Reset 'active' flag. cancelRefresh(ex); // Propagate exception to caller. throw ex; } finally { // Reset common introspection caches in Spring's core, since we // might not ever need metadata for singleton beans anymore... resetCommonCaches(); } } }
6.org.springframework.context.support.AbstractApplicationContext#obtainFreshBeanFactory()，注意方法里面的refreshBeanFactory()。
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() { refreshBeanFactory(); ConfigurableListableBeanFactory beanFactory = getBeanFactory(); if (logger.isDebugEnabled()) { logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory); } return beanFactory; }
7.org.springframework.context.support.AbstractRefreshableApplicationContext#refreshBeanFactory()，注意方法里面的loadBeanDefinitions(beanFactory)
@Override protected final void refreshBeanFactory() throws BeansException { if (hasBeanFactory()) { destroyBeans(); closeBeanFactory(); } try { DefaultListableBeanFactory beanFactory = createBeanFactory(); beanFactory.setSerializationId(getId()); customizeBeanFactory(beanFactory); loadBeanDefinitions(beanFactory); synchronized (this.beanFactoryMonitor) { this.beanFactory = beanFactory; } } catch (IOException ex) { throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex); } }
8.org.springframework.web.context.support.XmlWebApplicationContext#loadBeanDefinitions(DefaultListableBeanFactory beanFactory)，注意方法里面的loadBeanDefinitions(beanDefinitionReader)
@Override protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException { // Create a new XmlBeanDefinitionReader for the given BeanFactory. XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory); // Configure the bean definition reader with this context's // resource loading environment. beanDefinitionReader.setEnvironment(getEnvironment()); beanDefinitionReader.setResourceLoader(this);//将当前对象XmlWebApplicationContext作为资源加载器 beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this)); // Allow a subclass to provide custom initialization of the reader, // then proceed with actually loading the bean definitions. initBeanDefinitionReader(beanDefinitionReader); loadBeanDefinitions(beanDefinitionReader); }
9.org.springframework.web.context.support.XmlWebApplicationContext#loadBeanDefinitions(XmlBeanDefinitionReader reader)，注意方法里面的reader.loadBeanDefinitions(configLocation)
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException { String[] configLocations = getConfigLocations(); if (configLocations != null) { for (String configLocation : configLocations) {//注意String可能是通配符形式，每一个String可能会匹配多个xml文件 reader.loadBeanDefinitions(configLocation); } } }
10.org.springframework.beans.factory.support.AbstractBeanDefinitionReader#loadBeanDefinitions(String location)
@Override public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException { return loadBeanDefinitions(location, null); }
11.org.springframework.beans.factory.support.AbstractBeanDefinitionReader#loadBeanDefinitions(String location, Set<Resource> actualResources)，注意方法里面的loadBeanDefinitions(resources)
public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException { ResourceLoader resourceLoader = getResourceLoader();//获取资源加载器，即XmlWebApplicationContext实例 if (resourceLoader == null) { throw new BeanDefinitionStoreException( "Cannot import bean definitions from location [" + location + "]: no ResourceLoader available"); } if (resourceLoader instanceof ResourcePatternResolver) {//从类图可知关系 // Resource pattern matching available. try { Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);//加载资源文件 int loadCount = loadBeanDefinitions(resources); if (actualResources != null) { for (Resource resource : resources) { actualResources.add(resource); } } if (logger.isDebugEnabled()) { logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]"); } return loadCount; } catch (IOException ex) { throw new BeanDefinitionStoreException( "Could not resolve bean definition resource pattern [" + location + "]", ex); } } else { // Can only load single resources by absolute URL. Resource resource = resourceLoader.getResource(location); int loadCount = loadBeanDefinitions(resource); if (actualResources != null) { actualResources.add(resource); } if (logger.isDebugEnabled()) { logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]"); } return loadCount; } }
12.org.springframework.beans.factory.support.AbstractBeanDefinitionReader#loadBeanDefinitions(Resource... resources)，注意方法里面的loadBeanDefinitions(resource)
@Override public int loadBeanDefinitions(Resource... resources) throws BeanDefinitionStoreException { Assert.notNull(resources, "Resource array must not be null"); int counter = 0; for (Resource resource : resources) { counter += loadBeanDefinitions(resource);//处理每一个XML文件 } return counter; }
13.org.springframework.beans.factory.xml.XmlBeanDefinitionReader#loadBeanDefinitions(Resource resource)
@Override public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException { return loadBeanDefinitions(new EncodedResource(resource)); }
14.org.springframework.beans.factory.xml.XmlBeanDefinitionReader#loadBeanDefinitions(EncodedResource encodedResource)，注意doLoadBeanDefinitions(inputSource, encodedResource.getResource())
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException { Assert.notNull(encodedResource, "EncodedResource must not be null"); if (logger.isInfoEnabled()) { logger.info("Loading XML bean definitions from " + encodedResource); } Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get(); if (currentResources == null) { currentResources = new HashSet<EncodedResource>(4); this.resourcesCurrentlyBeingLoaded.set(currentResources); } if (!currentResources.add(encodedResource)) { throw new BeanDefinitionStoreException( "Detected cyclic loading of " + encodedResource + " - check your import definitions!"); } try { InputStream inputStream = encodedResource.getResource().getInputStream(); try { InputSource inputSource = new InputSource(inputStream); if (encodedResource.getEncoding() != null) { inputSource.setEncoding(encodedResource.getEncoding()); } return doLoadBeanDefinitions(inputSource, encodedResource.getResource()); } finally { inputStream.close(); } } catch (IOException ex) { throw new BeanDefinitionStoreException( "IOException parsing XML document from " + encodedResource.getResource(), ex); } finally { currentResources.remove(encodedResource); if (currentResources.isEmpty()) { this.resourcesCurrentlyBeingLoaded.remove(); } } }
15.org.springframework.beans.factory.xml.XmlBeanDefinitionReader#doLoadBeanDefinitions(InputSource inputSource, Resource resource)
Document doc = doLoadDocument(inputSource, resource); return registerBeanDefinitions(doc, resource);
16.org.springframework.beans.factory.xml.XmlBeanDefinitionReader#registerBeanDefinitions(Document doc, Resource resource)
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException { BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader(); int countBefore = getRegistry().getBeanDefinitionCount();//getRegistry()返回之前创建的DefaultListableBeanFactory documentReader.registerBeanDefinitions(doc, createReaderContext(resource)); return getRegistry().getBeanDefinitionCount() - countBefore; }
17.org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader#registerBeanDefinitions(Document doc, XmlReaderContext readerContext)
@Override public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) { this.readerContext = readerContext; logger.debug("Loading bean definitions"); Element root = doc.getDocumentElement(); doRegisterBeanDefinitions(root); }
18.org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader#doRegisterBeanDefinitions(Element root)，注意parseBeanDefinitions(root, this.delegate)
protected void doRegisterBeanDefinitions(Element root) { // Any nested <beans> elements will cause recursion in this method. In // order to propagate and preserve <beans> default-* attributes correctly, // keep track of the current (parent) delegate, which may be null. Create // the new (child) delegate with a reference to the parent for fallback purposes, // then ultimately reset this.delegate back to its original (parent) reference. // this behavior emulates a stack of delegates without actually necessitating one. BeanDefinitionParserDelegate parent = this.delegate; this.delegate = createDelegate(getReaderContext(), root, parent); if (this.delegate.isDefaultNamespace(root)) { String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE); if (StringUtils.hasText(profileSpec)) { String[] specifiedProfiles = StringUtils.tokenizeToStringArray( profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS); if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) { if (logger.isInfoEnabled()) { logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec + "] not matching: " + getReaderContext().getResource()); } return; } } } preProcessXml(root); parseBeanDefinitions(root, this.delegate); postProcessXml(root); this.delegate = parent; }
19.org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader#parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate)
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) { if (delegate.isDefaultNamespace(root)) { NodeList nl = root.getChildNodes(); for (int i = 0; i < nl.getLength(); i++) { Node node = nl.item(i); if (node instanceof Element) { Element ele = (Element) node; if (delegate.isDefaultNamespace(ele)) {//判断元素的名称空间是否为http://www.springframework.org/schema/beans parseDefaultElement(ele, delegate);//是 } else { delegate.parseCustomElement(ele);//否 } } } } else { delegate.parseCustomElement(root); } }
20.org.springframework.beans.factory.xml.BeanDefinitionParserDelegate#parseCustomElement(Element ele)
public BeanDefinition parseCustomElement(Element ele) { return parseCustomElement(ele, null); }
21.org.springframework.beans.factory.xml.BeanDefinitionParserDelegate#parseCustomElement(Element ele, BeanDefinition containingBd)
public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) { String namespaceUri = getNamespaceURI(ele);//对于dubbo标签，此处返回http://code.alibabatech.com/schema/dubbo NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);//即DefaultNamespaceHandlerResolver.resolve(String namespaceUri) if (handler == null) { error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele); return null; } return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd)); }
22.org.springframework.beans.factory.xml.DefaultNamespaceHandlerResolver#resolve(String namespaceUri)
@Override public NamespaceHandler resolve(String namespaceUri) { Map<String, Object> handlerMappings = getHandlerMappings();//返回所有名称空间和标签处理器的映射 Object handlerOrClassName = handlerMappings.get(namespaceUri);//通过名称空间uri获取 if (handlerOrClassName == null) { return null; } else if (handlerOrClassName instanceof NamespaceHandler) { return (NamespaceHandler) handlerOrClassName;//表明handler已经加载，直接返回实例 } else { String className = (String) handlerOrClassName; try { Class<?> handlerClass = ClassUtils.forName(className, this.classLoader);//加载handler，返回Class对象 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);//实例化handler namespaceHandler.init();//调用handler的init方法 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); } } }
23.org.springframework.beans.factory.xml.NamespaceHandlerSupport#parse(Element element, ParserContext parserContext)
@Override public BeanDefinition parse(Element element, ParserContext parserContext) { return findParserForElement(element, parserContext).parse(element, parserContext); }
24.org.springframework.beans.factory.xml.NamespaceHandlerSupport#findParserForElement(Element element, ParserContext parserContext)
//根据标签获取具体的解析器
private BeanDefinitionParser findParserForElement(Element element, ParserContext parserContext) { String localName = parserContext.getDelegate().getLocalName(element); BeanDefinitionParser parser = this.parsers.get(localName); if (parser == null) { parserContext.getReaderContext().fatal( "Cannot locate BeanDefinitionParser for element [" + localName + "]", element); } return parser; }
25.com.alibaba.dubbo.config.spring.schema.DubboBeanDefinitionParser#parse(Element element, ParserContext parserContext)
public BeanDefinition parse(Element element, ParserContext parserContext) { return parse(element, parserContext, beanClass, required); }
26.com.alibaba.dubbo.config.spring.schema.DubboBeanDefinitionParser#parse(Element element, ParserContext parserContext, Class<?> beanClass, boolean required)
