ApplicationContext类结构
context是一个存储上下文结构的东西，里面会引用BeanFactory 
BeanFactory类结构
我们从这句代码开始分析，(本文spring采用的是4.2.4的版本)
ApplicationContext con = new FileSystemXmlApplicationContext("src/test/java/com//spring/test/beans-factorybean.xml");
public FileSystemXmlApplicationContext(String... configLocations) throws BeansException { this(configLocations, true, null); } public FileSystemXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) throws BeansException { super(parent); setConfigLocations(configLocations); if (refresh) { refresh(); } } Spring IoC容器对Bean定义资源的载入是从refresh()函数开始的，refresh()是一个模板方法，refresh()方法的作用是：在创建IoC容器前，如果已经有容器存在，则需要把已有的容器销毁和关闭，以保证在refresh之后使用的是新建立起来的IoC容器。refresh的作用类似于对IoC容器的重启，在新建立好的容器中对容器进行初始化，对Bean定义资源进行载入
FileSystemXmlApplicationContext通过调用其父类AbstractApplicationContext的refresh()函数启动整个IoC容器对Bean定义的载入过程：
public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. prepareRefresh(); // 获取bean工厂 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(); } } } protected ConfigurableListableBeanFactory obtainFreshBeanFactory() { //这里使用了委派设计模式，父类定义了抽象的refreshBeanFactory()方法，具体实现调用子类容器的refreshBeanFactory()方法 refreshBeanFactory(); ConfigurableListableBeanFactory beanFactory = getBeanFactory(); if (logger.isDebugEnabled()) { logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory); } return beanFactory; } AbstractApplicationContext子类的refreshBeanFactory()方法：
AbstractApplicationContext类中只抽象定义了refreshBeanFactory()方法，容器真正调用的是其子类AbstractRefreshableApplicationContext实现的 refreshBeanFactory()方法
protected final void refreshBeanFactory() throws BeansException { if (hasBeanFactory()) { destroyBeans(); closeBeanFactory(); } try { DefaultListableBeanFactory beanFactory = createBeanFactory();//这里创建了一个默认的工厂 beanFactory.setSerializationId(getId()); customizeBeanFactory(beanFactory); loadBeanDefinitions(beanFactory); //此处进行加载 synchronized (this.beanFactoryMonitor) { this.beanFactory = beanFactory; } } catch (IOException ex) { throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex); } } AbstractRefreshableApplicationContext子类的loadBeanDefinitions方法：
AbstractRefreshableApplicationContext中只定义了抽象的loadBeanDefinitions方法，容器真正调用的是其子类AbstractXmlApplicationContext对该方法的实现，AbstractXmlApplicationContext的主要源码如下：
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException { // 通过这个XmlBeanDefinitionReader关联beanFactory，在解析的时候就注册到beanFactory里了 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); //进行初始化 } } 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); //通过reader来读取配置 } } 随后进入AbstractBeanDefinitionReader
public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException { Assert.notNull(locations, "Location array must not be null"); int counter = 0; for (String location : locations) { counter += loadBeanDefinitions(location);//每次加载一个配置文件 } return counter; } public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException { ResourceLoader resourceLoader = getResourceLoader(); if (resourceLoader == null) { throw new BeanDefinitionStoreException( "Cannot import bean definitions from location [" + location + "]: no ResourceLoader available"); } if (resourceLoader instanceof ResourcePatternResolver) { // Resource pattern matching available. try { Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location); int loadCount = loadBeanDefinitions(resources); //加载了多少个BeanDefinition ... return loadCount; } catch (IOException ex) { throw new BeanDefinitionStoreException( "Could not resolve bean definition resource pattern [" + location + "]", ex); } } ... } public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException { ... 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()); //稍稍封装了一下，这里进入加载 } finally { inputStream.close(); } } ... } protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException { try { Document doc = doLoadDocument(inputSource, resource); return registerBeanDefinitions(doc, resource); //解析成doc后开始注册beanDefinition } ... } public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException { BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader(); int countBefore = getRegistry().getBeanDefinitionCount(); //registry就是开始创建的那个beanFactory documentReader.registerBeanDefinitions(doc, createReaderContext(resource)); return getRegistry().getBeanDefinitionCount() - countBefore; } 进入子类DefaultBeanDefinitionDocumentReader执行registerBeanDefinitions方法
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) { this.readerContext = readerContext; logger.debug("Loading bean definitions"); Element root = doc.getDocumentElement(); doRegisterBeanDefinitions(root); } protected void doRegisterBeanDefinitions(Element root) { BeanDefinitionParserDelegate parent = this.delegate; this.delegate = createDelegate(getReaderContext(), root, parent); ... preProcessXml(root); parseBeanDefinitions(root, this.delegate); //对document进行解析 postProcessXml(root); this.delegate = parent; } protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) { //使用Spring默认的XML命名空间 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)) { parseDefaultElement(ele, delegate); //使用Spring的Bean规则解析元素节点 } else { delegate.parseCustomElement(ele); //没有使用Spring默认的XML命名空间，则使用用户自定义的解析规则解析元素节点 } } } } else { delegate.parseCustomElement(root); } } private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) { if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) { importBeanDefinitionResource(ele); } else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) { processAliasRegistration(ele); } else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) { processBeanDefinition(ele, delegate); //是bean的话就会进入处理,其他的不需要delegate帮忙 } else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) { // recurse doRegisterBeanDefinitions(ele); } } protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) { BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele); //用bdHolder封装了BeanDefinition if (bdHolder != null) { bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder); //有些自定义的schema再解析一遍，添加到beanDefinition里的propertyValue里 try { // 注册到最开始创建的beanFactory里 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)); } } BeanDefinitionParserDelegate继续进行进行解析
//参数containingBean标识<Bean>元素中是否包含子<Bean>元素 public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) { String id = ele.getAttribute(ID_ATTRIBUTE); String nameAttr = ele.getAttribute(NAME_ATTRIBUTE); ... String beanName = id; ... AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean); //解析 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); String beanClassName = beanDefinition.getBeanClassName(); if (beanClassName != null && beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() && !this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) { aliases.add(beanClassName);//把class的全路径添加到别名里了 } } ... } catch (Exception ex) { error(ex.getMessage(), ele); return null; } } String[] aliasesArray = StringUtils.toStringArray(aliases); return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray); //beanDefinition并没有beanId，所以连同beanName和别名数组一起放进bdHolder } return null; } 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); //创建beanDefinition parseBeanDefinitionAttributes(ele, beanName, containingBean, bd); //解析bean里定义的属性值 bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT)); parseMetaElements(ele, bd); parseLookupOverrideSubElements(ele, bd.getMethodOverrides()); parseReplacedMethodSubElements(ele, bd.getMethodOverrides()); parseConstructorArgElements(ele, bd); parsePropertyElements(ele, bd); //设置属性值 parseQualifierElements(ele, bd); 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; } protected AbstractBeanDefinition createBeanDefinition(String className, String parentName) throws ClassNotFoundException { return BeanDefinitionReaderUtils.createBeanDefinition( parentName, className, this.readerContext.getBeanClassLoader()); } public static AbstractBeanDefinition createBeanDefinition( String parentName, String className, ClassLoader classLoader) throws ClassNotFoundException { GenericBeanDefinition bd = new GenericBeanDefinition();//一个通用的beanDefition bd.setParentName(parentName); if (className != null) { if (classLoader != null) { bd.setBeanClass(ClassUtils.forName(className, classLoader)); } else { bd.setBeanClassName(className); } } return bd; } 解析好后生成的BeanDefinition，通过下面代码进行注册到beanFactoty中
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
public static void registerBeanDefinition( BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry) throws BeanDefinitionStoreException { String beanName = definitionHolder.getBeanName(); registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition()); //注册到beanFactoty中 String[] aliases = definitionHolder.getAliases(); if (aliases != null) { for (String alias : aliases) { registry.registerAlias(beanName, alias); //注册别名，放入aliasMap } } } 进入到DefaultListableBeanFactory，进行注册
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException { ... BeanDefinition oldBeanDefinition; oldBeanDefinition = this.beanDefinitionMap.get(beanName); if (oldBeanDefinition != null) { if (!isAllowBeanDefinitionOverriding()) { //是否允许覆盖bean,变量allowBeanDefinitionOverriding默认是true throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName + "': There is already [" + oldBeanDefinition + "] bound."); } ... this.beanDefinitionMap.put(beanName, beanDefinition); } else { if (hasBeanCreationStarted()) { ... } else { // 存入了map中 this.beanDefinitionMap.put(beanName, beanDefinition); this.beanDefinitionNames.add(beanName); this.manualSingletonNames.remove(beanName); } this.frozenBeanDefinitionNames = null; } if (oldBeanDefinition != null || containsSingleton(beanName)) { resetBeanDefinition(beanName); //清除map里的缓存 } } 在前面DefaultBeanDefinitionDocumentReader执行registerBeanDefinitions方法时有，delegate.parseCustomElement(root);这段代码会解析自定义标签比如：component-scan，开启自动包扫描
public BeanDefinition parseCustomElement(Element ele) {
return parseCustomElement(ele, null); } public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) { String namespaceUri = getNamespaceURI(ele); NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(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)); } //handler会帮忙找一个解析器来帮助解析 public BeanDefinition parse(Element element, ParserContext parserContext) { return findParserForElement(element, parserContext).parse(element, parserContext); } public BeanDefinition parse(Element element, ParserContext parserContext) { String basePackage = element.getAttribute(BASE_PACKAGE_ATTRIBUTE); basePackage = parserContext.getReaderContext().getEnvironment().resolvePlaceholders(basePackage); String[] basePackages = StringUtils.tokenizeToStringArray(basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);//获得要扫描的路径 // Actually scan for bean definitions and register them. ClassPathBeanDefinitionScanner scanner = configureScanner(parserContext, element); Set<BeanDefinitionHolder> beanDefinitions = scanner.doScan(basePackages); //scanner进行扫描 registerComponents(parserContext.getReaderContext(), beanDefinitions, element); return null; } protected Set<BeanDefinitionHolder> doScan(String... basePackages) { Assert.notEmpty(basePackages, "At least one base package must be specified"); Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<BeanDefinitionHolder>(); for (String basePackage : basePackages) { Set<BeanDefinition> candidates = findCandidateComponents(basePackage); //扫描指定包下的BD for (BeanDefinition candidate : candidates) { ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate); candidate.setScope(scopeMetadata.getScopeName());//默认单例 String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry); if (candidate instanceof AbstractBeanDefinition) { postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName); } if (candidate instanceof AnnotatedBeanDefinition) { AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate); } if (checkCandidate(beanName, candidate)) { BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName); definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry); beanDefinitions.add(definitionHolder); registerBeanDefinition(definitionHolder, this.registry); //注册到beanFactory } } } return beanDefinitions; } public Set<BeanDefinition> findCandidateComponents(String basePackage) { Set<BeanDefinition> candidates = new LinkedHashSet<BeanDefinition>(); try { String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX + resolveBasePackage(basePackage) + "/" + this.resourcePattern; Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath); ... for (Resource resource : resources) { ... if (resource.isReadable()) { try { MetadataReader metadataReader = this.metadataReaderFactory.getMetadataReader(resource); if (isCandidateComponent(metadataReader)) { ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader); //新的BD类型 ... } } catch (IOException ex) { throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex); } return candidates; } //新的BD public class ScannedGenericBeanDefinition extends GenericBeanDefinition implements AnnotatedBeanDefinition { ... }