ClassPathXmlApplicationContext 源代码阅读之我见

君不见长松卧壑困风霜，时来屹立扶明堂。这篇文章主要讲述ClassPathXmlApplicationContext 源代码阅读之我见相关的知识，希望能为你提供帮助。

由于本人的能力有限，只能说出自己的见解，如有错漏什么的，请大家批评指出。

由于代码封装太多，这里只列出了我认为的部分最重要的代码，一些简单的封装代码，不在下面列出。

由于代码太过于复杂，在本次博客中，只列出了关键的代码（包含代码在哪个类），具体的所有代码和细节，需要查看源码。

在源代码解读的时候，关键的方法代码，用红色字体，如：resolvePath(locations[i])。另外，所有具体的实现方法，都是以do开头的。

IOC容器生成，包括有定位、加载、注册三个步骤，下面介绍下xml配置方式的IOC容器的生成，通过注解方式生成的原理也是一样，不过要比这个简单些（不需要定位配置文件）。

ClassPathXmlApplicationContext：这是一个独立的xml的上下文bean，用于将普通的文件路劲加载解释、加载成为对应的bean，配置的路径方式可以是：/myfiles/context.xml 这种方式，也可以是：/myfiles/*-context 这种通配符的方式。

在ClassPathXmlApplicationContext中，有多个重载的构造方法，最重要的构造方法是：public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)。具体代码如下：

/** * Create a new ClassPathXmlApplicationContext with the given parent, * loading the definitions from the given XML files. * @param configLocations array of resource locations * @param refresh whether to automatically refresh the context, * loading all bean definitions and creating all singletons. * Alternatively, call refresh manually after further configuring the context. * @param parent the parent context * @throws BeansException if context creation failed * @see #refresh() */ //使用ApplicationContext容器创建一个ClassPathXmlApplicationContext容器，并从给定的xml文件中，加载定义的bean public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) throws BeansException {super(parent); //创建一个ApplicationContext　 setConfigLocations(configLocations); //为ApplicationContext 设置配置的位置（定位），如果没有设置，则使用默认的配置位置 if (refresh) { refresh(); //刷新容器，这个方法很重要 } }

下面介绍下setConfigLocations(configLocations)，源代码如下：

/** * Set the config locations for this application context.
* 为application context设置（一个或多个）配置文件 * If not set, the implementation may use a default as appropriate. */ public void setConfigLocations(String... locations) { if (locations != null) { Assert.noNullElements(locations, "Config locations must not be null"); this.configLocations = new String[locations.length]; for (int i = 0; i < locations.length; i++) { this.configLocations[i] = resolvePath(locations[i]).trim(); } } else { this.configLocations = null; } }

/** * Resolve the given path, replacing placeholders with corresponding * environment property values if necessary. Applied to config locations.
* 解析给定的路径，如果必要的话，用相应的环境属性值替换占位符来配置的位置，也就是${......} * @param path the original file path * @return the resolved file path * @see org.springframework.core.env.Environment#resolveRequiredPlaceholders(String) */ protected String resolvePath(String path) { return getEnvironment().resolveRequiredPlaceholders(path); }

//实现方法在orgspringframeworkspring-core4.3.13.RELEASEspring-core-4.3.13.RELEASE-sources.jar!
//orgspringframeworkcoreenvAbstractPropertyResolver.java类中@Override public String resolveRequiredPlaceholders(String text) throws IllegalArgumentException { if (this.strictHelper == null) { this.strictHelper = createPlaceholderHelper(false); } return doResolvePlaceholders(text, this.strictHelper); //真正的实现方法 }

/** * Replaces all placeholders of format {@code ${name}} with the value returned * from the supplied {@link PlaceholderResolver}.
* 替换所有的${name}的占位符 * @param value the value containing the placeholders to be replaced * @param placeholderResolver the {@code PlaceholderResolver} to use for replacement * @return the supplied value with placeholders replaced inline */ public String replacePlaceholders(String value, PlaceholderResolver placeholderResolver) { Assert.notNull(value, "‘value‘ must not be null"); return parseStringValue(value, placeholderResolver, new HashSet< String> ()); }

protected String parseStringValue( String value, PlaceholderResolver placeholderResolver, Set< String> visitedPlaceholders) {StringBuilder result = new StringBuilder(value); int startIndex = value.indexOf(this.placeholderPrefix); while (startIndex != -1) { int endIndex = findPlaceholderEndIndex(result, startIndex); if (endIndex != -1) { String placeholder = result.substring(startIndex + this.placeholderPrefix.length(), endIndex); String originalPlaceholder = placeholder; if (!visitedPlaceholders.add(originalPlaceholder)) {//判断是否有闭环调用的占位符 throw new IllegalArgumentException( "Circular placeholder reference ‘" + originalPlaceholder + "‘ in property definitions"); } // Recursive invocation, parsing placeholders contained in the placeholder key.
//递归调用，解析占位符键中包含的占位符。
placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders); // Now obtain the value for the fully resolved key...--现在获得完全解析键的值 String propVal = placeholderResolver.resolvePlaceholder(placeholder); if (propVal == null & & this.valueSeparator != null) { int separatorIndex = placeholder.indexOf(this.valueSeparator); if (separatorIndex != -1) { String actualPlaceholder = placeholder.substring(0, separatorIndex); String defaultValue = https://www.songbingjia.com/android/placeholder.substring(separatorIndex + this.valueSeparator.length()); propVal = placeholderResolver.resolvePlaceholder(actualPlaceholder); if (propVal == null) { propVal = defaultValue; } } } if (propVal != null) { // Recursive invocation, parsing placeholders contained in the // previously resolved placeholder value.
//递归调用，解析包含在先前解析的占位符值中的占位符
propVal = parseStringValue(propVal, placeholderResolver, visitedPlaceholders); result.replace(startIndex, endIndex + this.placeholderSuffix.length(), propVal); if (logger.isTraceEnabled()) { logger.trace("Resolved placeholder ‘" + placeholder + "‘"); } startIndex = result.indexOf(this.placeholderPrefix, startIndex + propVal.length()); } else if (this.ignoreUnresolvablePlaceholders) { // Proceed with unprocessed value.--处理未处理的占位符的值 startIndex = result.indexOf(this.placeholderPrefix, endIndex + this.placeholderSuffix.length()); } else { throw new IllegalArgumentException("Could not resolve placeholder ‘" + placeholder + "‘" + " in value "" + value + """); } visitedPlaceholders.remove(originalPlaceholder); } else { startIndex = -1; } }return result.toString(); }

跟踪查看，可以看到定位到的是这些形式的字符串：com.abc.model
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
继续跟进，查看 refresh() 方法，如下：

public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. //刷新前准备工作 prepareRefresh(); // Tell the subclass to refresh the internal bean factory. //通知子类刷新内部bean工厂，这里是抽象工厂模式，就是返回一个factory---在这一步，做了加载的动作，并且也注册了bean定义（这个在代码里的确看到这个
//） ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. //上下文使用bean工厂前准备工作，包括配置回调函数、不用注册的一些接口，默认的环境bean等一些标准的特性 prepareBeanFactory(beanFactory); try { // Allows post-processing of the bean factory in context subclasses. //允许子类中的bean工厂post操作，包括注册WebApplication特殊域如：request、response、sesseion、globalSession、application，还有注册环境bean，还有忽略一些接口 postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. //把工厂处理注册为上下文（context）中的bean，如果 invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. //注册用于拦截bean创建的bean处理器 registerBeanPostProcessors(beanFactory); // Initialize message source for this context. //初始化此上下文的消息源 initMessageSource(); // Initialize event multicaster for this context. //为上下文注册多（主机？转换）事件 initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses. onRefresh(); // Check for listener beans and register them. //初始化特定上下文子类中的其他特殊bean registerListeners(); // Instantiate all remaining (non-lazy-init) singletons. //实例化所有持有的(非延迟-init)单例 finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event. //最后一步：发布相应的事件 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. //销毁已经创建的单例bean，以避免资源浪费 destroyBeans(); // Reset ‘active‘ flag. //重置存活标志 cancelRefresh(ex); // Propagate exception to caller. //抛出异常 throw ex; }finally { // Reset common introspection caches in Spring‘s core, since we // might not ever need metadata for singleton beans anymore... //重置spring 中的公共缓存，因为可能永远都不再需要这个bean resetCommonCaches(); } } }

下面查看 obtainFreshBeanFactory()方法

/** * Tell the subclass to refresh the internal bean factory.
* 告诉子类刷新内部bean工厂 * @return the fresh BeanFactory instance * @see #refreshBeanFactory() * @see #getBeanFactory() */ protected ConfigurableListableBeanFactory obtainFreshBeanFactory() { refreshBeanFactory(); ConfigurableListableBeanFactory beanFactory = getBeanFactory(); if (logger.isDebugEnabled()) { logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory); } return beanFactory; }

//orgspringframeworkspring-context4.3.13.RELEASEspring-context-4.3.13.RELEASE-sources.jar!orgspringframeworkcontextsupportAbstractRefreshableApplicationContext.java/** * This implementation performs an actual refresh of this context‘s underlying * bean factory, shutting down the previous bean factory (if any) and * initializing a fresh bean factory for the next phase of the context‘s lifecycle.
*真正地实现对上下文的基础bean工厂执行实际的刷新，如果之前有了工厂，则关闭前一个bean工厂，并为上下文生命周期的下一阶段初始化一个新的bean工厂。 */ @Override protected final void refreshBeanFactory() throws BeansException { if (hasBeanFactory()) { destroyBeans(); //销毁bean closeBeanFactory(); //关闭bean工厂 } try { DefaultListableBeanFactory beanFactory = createBeanFactory(); beanFactory.setSerializationId(getId());
//这里允许自定义bean工厂 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); } }

//orgspringframeworkspring-context4.3.13.RELEASEspring-context-4.3.13.RELEASE-sources.jar!orgspringframeworkcontextsupportAbstractXmlApplicationContext.java/** * Loads the bean definitions via an XmlBeanDefinitionReader.
* 通过XmlBeanDefinitionReader装载bean定义 * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader * @see #initBeanDefinitionReader * @see #loadBeanDefinitions */ @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(this.getEnvironment()); beanDefinitionReader.setResourceLoader(this); 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); }

/** * Load the bean definitions with the given XmlBeanDefinitionReader.
* 使用给定的xmlBeanDefinitionReader加载Bean 定义 * The lifecycle of the bean factory is handled by the {@link #refreshBeanFactory} * method; hence this method is just supposed to load and/or register bean definitions. * @param reader the XmlBeanDefinitionReader to use * @throws BeansException in case of bean registration errors * @throws IOException if the required XML document isn‘t found * @see #refreshBeanFactory * @see #getConfigLocations * @see #getResources * @see #getResourcePatternResolver */ protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException { Resource[] configResources = getConfigResources(); if (configResources != null) { reader.loadBeanDefinitions(configResources); } String[] configLocations = getConfigLocations(); if (configLocations != null) { reader.loadBeanDefinitions(configLocations); } }

// 这里使用循环，证明可以加载多个配置文件
@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); } return counter; }

//orgspringframeworkspring-beans4.3.13.RELEASEspring-beans-4.3.13.RELEASE-sources.jar!orgspringframeworkeansfactorygroovyGroovyBeanDefinitionReader.java
/** * Load bean definitions from the specified Groovy script or XML file.
* 从指定的Groovy脚本或XML文件加载bean定义 * Note that {@code ".xml"} files will be parsed as XML content; all other kinds * of resources will be parsed as Groovy scripts. * @param resource the resource descriptor for the Groovy script or XML file * @return the number of bean definitions found * @throws BeanDefinitionStoreException in case of loading or parsing errors */ public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException { return loadBeanDefinitions(new EncodedResource(resource)); }

/** * Load bean definitions from the specified Groovy script or XML file.
* 从指定的Groovy脚本或XML文件加载bean定义 * Note that {@code ".xml"} files will be parsed as XML content; all other kinds * of resources will be parsed as Groovy scripts. * @param encodedResource the resource descriptor for the Groovy script or XML file, * allowing specification of an encoding to use for parsing the file * @return the number of bean definitions found * @throws BeanDefinitionStoreException in case of loading or parsing errors */ public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException { // Check for XML files and redirect them to the "standard" XmlBeanDefinitionReader String filename = encodedResource.getResource().getFilename(); if (StringUtils.endsWithIgnoreCase(filename, ".xml")) { return this.standardXmlBeanDefinitionReader.loadBeanDefinitions(encodedResource); }Closure beans = new Closure(this) { public Object call(Object[] args) { invokeBeanDefiningClosure((Closure) args[0]); return null; } }; Binding binding = new Binding() { @Override public void setVariable(String name, Object value) { if (currentBeanDefinition != null) { applyPropertyToBeanDefinition(name, value); } else { super.setVariable(name, value); } } }; binding.setVariable("beans", beans); int countBefore = getRegistry().getBeanDefinitionCount(); try { GroovyShell shell = new GroovyShell(getResourceLoader().getClassLoader(), binding); shell.evaluate(encodedResource.getReader(), "beans"); } catch (Throwable ex) { throw new BeanDefinitionParsingException(new Problem("Error evaluating Groovy script: " + ex.getMessage(), new Location(encodedResource.getResource()), null, ex)); } return getRegistry().getBeanDefinitionCount() - countBefore; }

/** * Load bean definitions from the specified XML file. * @param encodedResource the resource descriptor for the XML file, * allowing to specify an encoding to use for parsing the file * @return the number of bean definitions found * @throws BeanDefinitionStoreException in case of loading or parsing errors */ 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.getResource()); }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(); } } }

/** * Actually load bean definitions from the specified XML file.
* 从指定的xml文件中，实际执行加载bean定义的方法 * @param inputSource the SAX InputSource to read from * @param resource the resource descriptor for the XML file * @return the number of bean definitions found * @throws BeanDefinitionStoreException in case of loading or parsing errors * @see #doLoadDocument * @see #registerBeanDefinitions */ protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException { try { Document doc = doLoadDocument(inputSource, resource); return registerBeanDefinitions(doc, resource); } catch (BeanDefinitionStoreException ex) { throw ex; } catch (SAXParseException ex) { throw new XmlBeanDefinitionStoreException(resource.getDescription(), "Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex); } catch (SAXException ex) { throw new XmlBeanDefinitionStoreException(resource.getDescription(), "XML document from " + resource + " is invalid", ex); } catch (ParserConfigurationException ex) { throw new BeanDefinitionStoreException(resource.getDescription(), "Parser configuration exception parsing XML from " + resource, ex); } catch (IOException ex) { throw new BeanDefinitionStoreException(resource.getDescription(), "IOException parsing XML document from " + resource, ex); } catch (Throwable ex) { throw new BeanDefinitionStoreException(resource.getDescription(), "Unexpected exception parsing XML document from " + resource, ex); } }

/** * Register the bean definitions contained in the given DOM document.--注册包含在给定的dom中的bean定义 * Called by {@code loadBeanDefinitions}. * Creates a new instance of the parser class and invokes * {@code registerBeanDefinitions} on it. * @param doc the DOM document * @param resource the resource descriptor (for context information) * @return the number of bean definitions found * @throws BeanDefinitionStoreException in case of parsing errors * @see #loadBeanDefinitions * @see #setDocumentReaderClass * @see BeanDefinitionDocumentReader#registerBeanDefinitions */ public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException { BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader(); int countBefore = getRegistry().getBeanDefinitionCount(); documentReader.registerBeanDefinitions(doc, createReaderContext(resource)); return getRegistry().getBeanDefinitionCount() - countBefore; }

//orgspringframeworkspring-beans4.3.13.RELEASEspring-beans-4.3.13.RELEASE-sources.jar!orgspringframeworkeansfactoryxmlDefaultBeanDefinitionDocumentReader.java/** * This implementation parses bean definitions according to the "spring-beans" XSD
* 根据“spring-beans”XSD解析bean定义 * (or DTD, historically). * Opens a DOM Document; then initializes the default settings * specified at the {@code < beans/> } level; then parses the contained bean definitions. */ @Override public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) { this.readerContext = readerContext; logger.debug("Loading bean definitions"); Element root = doc.getDocumentElement(); doRegisterBeanDefinitions(root); }

/** * Register each bean definition within the given root {@code < beans/> } element.
* 注册根节点内的每一个bean定义 */ 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; }

/** * Parse the elements at the root level in the document:-转换根节点 * "import", "alias", "bean". * @param root the DOM root element of the document */ 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;
//判断是否是默认的命名空间：http://www.springframework.org/schema/beans，一般情况下我们都是放在这个命名空间下 if (delegate.isDefaultNamespace(ele)) { parseDefaultElement(ele, delegate); } else { delegate.parseCustomElement(ele); } } } } else { delegate.parseCustomElement(root); } }

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) { if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {//import 标签 importBeanDefinitionResource(ele); } else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {//alias标签 processAliasRegistration(ele); } else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {//bean 标签 processBeanDefinition(ele, delegate); } else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {//beans标签。注意，这里有递归调用。这里实际上也调用了上面的processBeanDefinition方法 // recurse doRegisterBeanDefinitions(ele); } }

/** * Process the given bean element, parsing the bean definition--转换成bean定义 * and registering it with the registry. */ protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) { BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele); if (bdHolder != null) { bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder); try { // Register the final decorated instance. BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry()); } catch (BeanDefinitionStoreException ex) { getReaderContext().error("Failed to register bean definition with name ‘" + bdHolder.getBeanName() + "‘", ele, ex); } // Send registration event. getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder)); } }

/** * Parses the supplied {@code < bean> } element. May return {@code null} * if there were errors during parse. Errors are reported to the * {@link org.springframework.beans.factory.parsing.ProblemReporter}. */ public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) { return parseBeanDefinitionElement(ele, null); }/** * Parses the supplied {@code < bean> } element. May return {@code null} * if there were errors during parse. Errors are reported to the * {@link org.springframework.beans.factory.parsing.ProblemReporter}. */ public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) { String id = ele.getAttribute(ID_ATTRIBUTE); String nameAttr = ele.getAttribute(NAME_ATTRIBUTE); List< String> aliases = new ArrayList< String> (); if (StringUtils.hasLength(nameAttr)) { String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS); aliases.addAll(Arrays.asList(nameArr)); }String beanName = id; if (!StringUtils.hasText(beanName) & & !aliases.isEmpty()) { beanName = aliases.remove(0); if (logger.isDebugEnabled()) { logger.debug("No XML ‘id‘ specified - using ‘" + beanName + "‘ as bean name and " + aliases + " as aliases"); } }if (containingBean == null) { checkNameUniqueness(beanName, aliases, ele); }AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean); if (beanDefinition != null) { if (!StringUtils.hasText(beanName)) { try { if (containingBean != null) { beanName = BeanDefinitionReaderUtils.generateBeanName( beanDefinition, this.readerContext.getRegistry(), true); } else { beanName = this.readerContext.generateBeanName(beanDefinition); // Register an alias for the plain bean class name, if still possible, // if the generator returned the class name plus a suffix. // This is expected for Spring 1.2/2.0 backwards compatibility. String beanClassName = beanDefinition.getBeanClassName(); if (beanClassName != null & & beanName.startsWith(beanClassName) & & beanName.length() > beanClassName.length() & & !this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) { aliases.add(beanClassName); } } if (logger.isDebugEnabled()) { logger.debug("Neither XML ‘id‘ nor ‘name‘ specified - " + "using generated bean name [" + beanName + "]"); } } catch (Exception ex) { error(ex.getMessage(), ele); return null; } } String[] aliasesArray = StringUtils.toStringArray(aliases); return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray); }return null; }

/** * Parse the bean definition itself, without regard to name or aliases. May return
* 解析bean定义本身，而不考虑名称或别名 * {@code null} if problems occurred during the parsing of the bean definition. */ public AbstractBeanDefinition parseBeanDefinitionElement( Element ele, String beanName, BeanDefinition containingBean) {this.parseState.push(new BeanEntry(beanName)); String className = null; if (ele.hasAttribute(CLASS_ATTRIBUTE)) { className = ele.getAttribute(CLASS_ATTRIBUTE).trim(); }try { String parent = null; if (ele.hasAttribute(PARENT_ATTRIBUTE)) { parent = ele.getAttribute(PARENT_ATTRIBUTE); } AbstractBeanDefinition bd = createBeanDefinition(className, parent);
//将给定bean元素的属性应用于给定bean *定义，如：singleton、scope、abstract、lazy-init 等属性 parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
//设置描述为可阅读 bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
//设置元数据属性 parseMetaElements(ele, bd);
//解析查找覆盖给定bean元素的子元素 parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
//解释给定的bean的子元素的替换方法 parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
//解释给定bean元素的构造函数的子元素 parseConstructorArgElements(ele, bd);
//解释给定的bean元素的子元素的属性 parsePropertyElements(ele, bd);
//解释给定的bean元素的子元素的限定符 parseQualifierElements(ele, bd);
//设置bean定义的来源 bd.setResource(this.readerContext.getResource()); bd.setSource(extractSource(ele)); return bd; } catch (ClassNotFoundException ex) { error("Bean class [" + className + "] not found", ele, ex); } catch (NoClassDefFoundError err) { error("Class that bean class [" + className + "] depends on not found", ele, err); } catch (Throwable ex) { error("Unexpected failure during bean definition parsing", ele, ex); } finally { this.parseState.pop(); }return null; }

下面贴出加载xml文件中的属性配置的源代码

/** * Parse property sub-elements of the given bean element. */ public void parsePropertyElements(Element beanEle, BeanDefinition bd) { NodeList nl = beanEle.getChildNodes(); for (int i = 0; i < nl.getLength(); i++) { Node node = nl.item(i); if (isCandidateElement(node) & & nodeNameEquals(node, PROPERTY_ELEMENT)) { parsePropertyElement((Element) node, bd); } } }

/** * Parse a property element. */ public void parsePropertyElement(Element ele, BeanDefinition bd) { String propertyName = ele.getAttribute(NAME_ATTRIBUTE); if (!StringUtils.hasLength(propertyName)) { error("Tag ‘property‘ must have a ‘name‘ attribute", ele); return; } this.parseState.push(new PropertyEntry(propertyName)); try { if (bd.getPropertyValues().contains(propertyName)) { error("Multiple ‘property‘ definitions for property ‘" + propertyName + "‘", ele); return; } Object val = parsePropertyValue(ele, bd, propertyName); PropertyValue pv = new PropertyValue(propertyName, val); parseMetaElements(ele, pv); pv.setSource(extractSource(ele)); bd.getPropertyValues().addPropertyValue(pv); } finally { this.parseState.pop(); } }

/** * Get the value of a property element. May be a list etc. * Also used for constructor arguments, "propertyName" being null in this case. */ public Object parsePropertyValue(Element ele, BeanDefinition bd, String propertyName) { String elementName = (propertyName != null) ? "< property> element for property ‘" + propertyName + "‘" : "< constructor-arg> element"; // Should only have one child element: ref, value, list, etc. NodeList nl = ele.getChildNodes(); Element subElement = null; for (int i = 0; i < nl.getLength(); i++) { Node node = nl.item(i); if (node instanceof Element & & !nodeNameEquals(node, DESCRIPTION_ELEMENT) & & !nodeNameEquals(node, META_ELEMENT)) { // Child element is what we‘re looking for. if (subElement != null) { error(elementName + " must not contain more than one sub-element", ele); } else { subElement = (Element) node; } } }boolean hasRefAttribute = ele.hasAttribute(REF_ATTRIBUTE); boolean hasValueAttribute = ele.hasAttribute(VALUE_ATTRIBUTE); if ((hasRefAttribute & & hasValueAttribute) || ((hasRefAttribute || hasValueAttribute) & & subElement != null)) { error(elementName + " is only allowed to contain either ‘ref‘ attribute OR ‘value‘ attribute OR sub-element", ele); }if (hasRefAttribute) { String refName = ele.getAttribute(REF_ATTRIBUTE); if (!StringUtils.hasText(refName)) { error(elementName + " contains empty ‘ref‘ attribute", ele); } RuntimeBeanReference ref = new RuntimeBeanReference(refName); ref.setSource(extractSource(ele)); return ref; } else if (hasValueAttribute) { TypedStringValue valueHolder = new TypedStringValue(ele.getAttribute(VALUE_ATTRIBUTE)); valueHolder.setSource(extractSource(ele)); return valueHolder; } else if (subElement != null) { return parsePropertySubElement(subElement, bd); } else { // Neither child element nor "ref" or "value" attribute found. error(elementName + " must specify a ref or value", ele); return null; } }

public Object parsePropertySubElement(Element ele, BeanDefinition bd) { return parsePropertySubElement(ele, bd, null); }/** * Parse a value, ref or collection sub-element of a property or * constructor-arg element. * @param ele subelement of property element; we don‘t know which yet * @param defaultValueType the default type (class name) for any * {@code < value> } tag that might be created */ public Object parsePropertySubElement(Element ele, BeanDefinition bd, String defaultValueType) { if (!isDefaultNamespace(ele)) { return parseNestedCustomElement(ele, bd); } else if (nodeNameEquals(ele, BEAN_ELEMENT)) { BeanDefinitionHolder nestedBd = parseBeanDefinitionElement(ele, bd); if (nestedBd != null) { nestedBd = decorateBeanDefinitionIfRequired(ele, nestedBd, bd); } return nestedBd; } else if (nodeNameEquals(ele, REF_ELEMENT)) { // A generic reference to any name of any bean. String refName = ele.getAttribute(BEAN_REF_ATTRIBUTE); boolean toParent = false; if (!StringUtils.hasLength(refName)) { // A reference to the id of another bean in the same XML file. refName = ele.getAttribute(LOCAL_REF_ATTRIBUTE); if (!StringUtils.hasLength(refName)) { // A reference to the id of another bean in a parent context. refName = ele.getAttribute(PARENT_REF_ATTRIBUTE); toParent = true; if (!StringUtils.hasLength(refName)) { error("‘bean‘, ‘local‘ or ‘parent‘ is required for < ref> element", ele); return null; } } } if (!StringUtils.hasText(refName)) { error("< ref> element contains empty target attribute", ele); return null; } RuntimeBeanReference ref = new RuntimeBeanReference(refName, toParent); ref.setSource(extractSource(ele)); return ref; } else if (nodeNameEquals(ele, IDREF_ELEMENT)) { return parseIdRefElement(ele); } else if (nodeNameEquals(ele, VALUE_ELEMENT)) { return parseValueElement(ele, defaultValueType); } else if (nodeNameEquals(ele, NULL_ELEMENT)) { // It‘s a distinguished null value. Let‘s wrap it in a TypedStringValue // object in order to preserve the source location. TypedStringValue nullHolder = new TypedStringValue(null); nullHolder.setSource(extractSource(ele)); return nullHolder; } else if (nodeNameEquals(ele, ARRAY_ELEMENT)) { return parseArrayElement(ele, bd); } else if (nodeNameEquals(ele, LIST_ELEMENT)) { return parseListElement(ele, bd); } else if (nodeNameEquals(ele, SET_ELEMENT)) { return parseSetElement(ele, bd); } else if (nodeNameEquals(ele, MAP_ELEMENT)) { return parseMapElement(ele, bd); } else if (nodeNameEquals(ele, PROPS_ELEMENT)) { return parsePropsElement(ele); } else { error("Unknown property sub-element: [" + ele.getNodeName() + "]", ele); return null; } }

从上面可以看到，xml中支持的map、list、set、props、array这些属性，都是在这里方法中进行最终的处理。以上的代码，是比较关键的加载bean的代码
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下面阅读 invokeBeanFactoryPostProcessors(beanFactory)

/** * Instantiate and invoke all registered BeanFactoryPostProcessor beans, * respecting explicit order if given. * Must be called before singleton instantiation. */

//初始化bean并执行所有已经注册bean工厂后置处理器，如果有排序，则按照排序进行处理华
//这里要注意的：必须在单例bean的实例化之前执行这个bean工厂的初始化，因为单例模式是程序运行的时候就已经创建，而普通bean则是在调用时候，才会初始化 protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) { PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors()); // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor) if (beanFactory.getTempClassLoader() == null & & beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) { beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory)); beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader())); } }

public static void invokeBeanFactoryPostProcessors( ConfigurableListableBeanFactory beanFactory, List< BeanFactoryPostProcessor> beanFactoryPostProcessors) {// Invoke BeanDefinitionRegistryPostProcessors first, if any. Set< String> processedBeans = new HashSet< String> ();
//如果是注册的工厂bean，则先于普通的bean先初始化 if (beanFactory instanceof BeanDefinitionRegistry) { BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory; List< BeanFactoryPostProcessor> regularPostProcessors = new LinkedList< BeanFactoryPostProcessor> (); List< BeanDefinitionRegistryPostProcessor> registryProcessors = new LinkedList< BeanDefinitionRegistryPostProcessor> (); for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) { if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) { BeanDefinitionRegistryPostProcessor registryProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor; registryProcessor.postProcessBeanDefinitionRegistry(registry); registryProcessors.add(registryProcessor); } else { regularPostProcessors.add(postProcessor); } }// Do not initialize FactoryBeans here: We need to leave all regular beans // uninitialized to let the bean factory post-processors apply to them! // Separate between BeanDefinitionRegistryPostProcessors that implement // PriorityOrdered, Ordered, and the rest.

//不要在这里初始化factorybean:因为需要保证所有的普通的bean在后置处理器中使用到（我想应该是调用的时候会用到吧，这个不确定）

List< BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList< BeanDefinitionRegistryPostProcessor> ();

// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
// 首先，先初始化实现（使用）PriorityOrdered接口的bean

String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); for (String ppName : postProcessorNames) { if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); processedBeans.add(ppName); } } sortPostProcessors(currentRegistryProcessors, beanFactory); registryProcessors.addAll(currentRegistryProcessors); invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); currentRegistryProcessors.clear(); //这里有清理动作，也就是设置为null// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
// 接下来，执行实现了Ordered接口的注册（性质）的后置工厂处理器
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); for (String ppName : postProcessorNames) { if (!processedBeans.contains(ppName) & & beanFactory.isTypeMatch(ppName, Ordered.class)) { currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); processedBeans.add(ppName); } } sortPostProcessors(currentRegistryProcessors, beanFactory); registryProcessors.addAll(currentRegistryProcessors); invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); currentRegistryProcessors.clear(); // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
//最后，执行所有其他的注册（性质的）bean工厂后置处理器
boolean reiterate = true; while (reiterate) { reiterate = false; postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); for (String ppName : postProcessorNames) { if (!processedBeans.contains(ppName)) { currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); processedBeans.add(ppName); reiterate = true; } } sortPostProcessors(currentRegistryProcessors, beanFactory); registryProcessors.addAll(currentRegistryProcessors); invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); currentRegistryProcessors.clear(); }// Now, invoke the postProcessBeanFactory callback of all processors handled so far. invokeBeanFactoryPostProcessors(registryProcessors, beanFactory); invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory); }else { // Invoke factory processors registered with the context instance.
// 执行上下文注册的工厂后置处理器，我们自定义的bean就是在这一步执行
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory); }// Do not initialize FactoryBeans here: We need to leave all regular beans // uninitialized to let the bean factory post-processors apply to them! String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false); // Separate between BeanFactoryPostProcessors that implement PriorityOrdered, // Ordered, and the rest. List< BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList< BeanFactoryPostProcessor> (); List< String> orderedPostProcessorNames = new ArrayList< String> (); List< String> nonOrderedPostProcessorNames = new ArrayList< String> (); for (String ppName : postProcessorNames) { if (processedBeans.contains(ppName)) { // skip - already processed in first phase above } else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class)); } else if (beanFactory.isTypeMatch(ppName, Ordered.class)) { orderedPostProcessorNames.add(ppName); } else { nonOrderedPostProcessorNames.add(ppName); } }// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered. sortPostProcessors(priorityOrderedPostProcessors, beanFactory); invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory); // Next, invoke the BeanFactoryPostProcessors that implement Ordered. List< BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList< BeanFactoryPostProcessor> (); for (String postProcessorName : orderedPostProcessorNames) { orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class)); } sortPostProcessors(orderedPostProcessors, beanFactory); invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory); // Finally, invoke all other BeanFactoryPostProcessors. List< BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList< BeanFactoryPostProcessor> (); for (String postProcessorName : nonOrderedPostProcessorNames) { nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class)); } invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory); // Clear cached merged bean definitions since the post-processors might have // modified the original metadata, e.g. replacing placeholders in values... beanFactory.clearMetadataCache(); }

上面要注意几点：1、执行初始化工厂后置处理器，不会实例化已加载定义的bean 2、初始化工厂后置处理器，必须在单例bean的实例化之前，因为单例bean是运行时候就已经实例化 3、初始化的执行，是有顺序的
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下面阅读 registerBeanPostProcessors(beanFactory)

/** * Instantiate and invoke all registered BeanPostProcessor beans, * respecting explicit order if given. * Must be called before any instantiation of application beans. */
//初始化并执行所有已注册的bean后置处理器bean，如果有排序，则按照排序进行初始化和执行。
//必须在任何上下文bean实例化之前调用，（不确定）是因为上下文的bean是在运行时候就已经实例化
protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) { PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this); //这里是个委托模式 }

public static void registerBeanPostProcessors( ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false); // Register BeanPostProcessorChecker that logs an info message when // a bean is created during BeanPostProcessor instantiation, i.e. when // a bean is not eligible for getting processed by all BeanPostProcessors.
//注册BeanPostProcessorChecker，它记录信息消息bean是在BeanPostProcessor实例化期间创建的，
//也就是说，当bean不适合由所有BeanPostProcessor进行处理时。-----

int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length; beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount)); // Separate between BeanPostProcessors that implement PriorityOrdered, // Ordered, and the rest. List< BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList< BeanPostProcessor> (); List< BeanPostProcessor> internalPostProcessors = new ArrayList< BeanPostProcessor> (); List< String> orderedPostProcessorNames = new ArrayList< String> (); List< String> nonOrderedPostProcessorNames = new ArrayList< String> (); for (String ppName : postProcessorNames) { if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class); priorityOrderedPostProcessors.add(pp); if (pp instanceof MergedBeanDefinitionPostProcessor) { internalPostProcessors.add(pp); } } else if (beanFactory.isTypeMatch(ppName, Ordered.class)) { orderedPostProcessorNames.add(ppName); } else { nonOrderedPostProcessorNames.add(ppName); } }// First, register the BeanPostProcessors that implement PriorityOrdered. sortPostProcessors(priorityOrderedPostProcessors, beanFactory); registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors); // Next, register the BeanPostProcessors that implement Ordered. List< BeanPostProcessor> orderedPostProcessors = new ArrayList< BeanPostProcessor> (); for (String ppName : orderedPostProcessorNames) { BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class); orderedPostProcessors.add(pp); if (pp instanceof MergedBeanDefinitionPostProcessor) { internalPostProcessors.add(pp); } } sortPostProcessors(orderedPostProcessors, beanFactory); registerBeanPostProcessors(beanFactory, orderedPostProcessors); // Now, register all regular BeanPostProcessors. List< BeanPostProcessor> nonOrderedPostProcessors = new ArrayList< BeanPostProcessor> (); for (String ppName : nonOrderedPostProcessorNames) { BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class); nonOrderedPostProcessors.add(pp); if (pp instanceof MergedBeanDefinitionPostProcessor) { internalPostProcessors.add(pp); } } registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors); // Finally, re-register all internal BeanPostProcessors.
// 重注册所有的内部bean后置处理器（为什么呢？）
sortPostProcessors(internalPostProcessors, beanFactory); registerBeanPostProcessors(beanFactory, internalPostProcessors); // Re-register post-processor for detecting inner beans as ApplicationListeners, // moving it to the end of the processor chain (for picking up proxies etc).
//重新注册后处理器以检测内部bean作为applicationlistener，将其移动到处理器链的末尾(用于获取代理等)
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext)); }

上面这段代码，跟invokeBeanFactoryPostProcessors(beanFactory) 很像是吧。惊不惊喜，意不意外！

Override public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) { Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null"); this.beanPostProcessors.remove(beanPostProcessor); this.beanPostProcessors.add(beanPostProcessor); if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) { this.hasInstantiationAwareBeanPostProcessors = true; } if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) { this.hasDestructionAwareBeanPostProcessors = true; } }

/** BeanPostProcessors to apply in createBean */ private final List< BeanPostProcessor> beanPostProcessors = new ArrayList< BeanPostProcessor> ();

查看这个addProcessor，其实就是在一个list里面先remove，然后add

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到目前为止，已经阅读完所有的关键代码。当然了，由于本人水平有限，也是第一次阅读这个代码，中间肯定有很多理解不到位，甚至错误的地方，请各位大神批评指正。欢迎留言交流。
【ClassPathXmlApplicationContext 源代码阅读之我见】