第一次跟着看源码，记录一下！（我是谁？我在哪？我怎么走到这步的？！）
首先定位入口：ClassPathXmlApplicationContext类的构造方法
/**
* 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()
*/
public ClassPathXmlApplicationContext(
String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
throws BeansException {
//调用父类构造为容器设置好Bean资源加载器
super(parent);
//调用父类的setConfigLocations解析设置Bean定义资源文件的路径
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}
构造方法一路向上，在祖先类AbstractApplicationContext有如下过程
/**
* Create a new AbstractApplicationContext with no parent.
*/
public AbstractApplicationContext() {
this.resourcePatternResolver = getResourcePatternResolver();
}
/**
* Create a new AbstractApplicationContext with the given parent context.
* @param parent the parent context
*/
public AbstractApplicationContext(@Nullable ApplicationContext parent) {
this();
setParent(parent);
}
...
/**
* Return the ResourcePatternResolver to use for resolving location patterns
* into Resource instances. Default is a
* {@link org.springframework.core.io.support.PathMatchingResourcePatternResolver},
* supporting Ant-style location patterns.
* <p>Can be overridden in subclasses, for extended resolution strategies,
* for example in a web environment.
* <p><b>Do not call this when needing to resolve a location pattern.</b>
* Call the context's {@code getResources} method instead, which
* will delegate to the ResourcePatternResolver.
* @return the ResourcePatternResolver for this context
* @see #getResources
* @see org.springframework.core.io.support.PathMatchingResourcePatternResolver
*/
//获取一个Spring Source的加载器用于读入Spring Bean定义资源文件
protected ResourcePatternResolver getResourcePatternResolver() {
//AbstractApplicationContext继承DefaultResourceLoader，因此也是一个资源加载器
//Spring资源加载器，其getResource(String location)方法用于载入资源
return new PathMatchingResourcePatternResolver(this);
}
设置完容器的资源加载器后，调用父类的setConfigLocations解析定位Bean定义资源文件。SpringIOC在初始化时将这些资源文件定位为Spring封装的Resource
/**
* Set the config locations for this application context.
* <p>If not set, the implementation may use a default as appropriate.
*/
//解析Bean定义资源文件的路径，处理多个资源文件字符串数组
public void setConfigLocations(@Nullable 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++) {
// resolvePath为同一个类中将字符串解析为路径的方法
this.configLocations[i] = resolvePath(locations[i]).trim();
}
}
else {
this.configLocations = null;
}
}
接着调用AbstractApplicationContext中的refresh（注：这是个模板方法）对建立好的容器进行初始化，对Bean定义资源进行载入，若在执行该方法时已存在其他容器，则销毁其他容器。
refresh主要为IOC容器Bean的生命周期管理提供条件，SpringIOC容器载入Bean定义资源文件从其子类容器的refreshBeanFactory方法启动，所以ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();启动载入过程，之后的代码都是注册容器的信息源和生命周期事件。
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
//调用容器准备刷新的方法，获取容器的当时时间，同时给容器设置同步标识
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
//告诉子类启动refreshBeanFactory()方法，Bean定义资源文件的载入从
//子类的refreshBeanFactory()方法启动
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
//为BeanFactory配置容器特性，例如类加载器、事件处理器等
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
//为容器的某些子类指定特殊的BeanPost事件处理器
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
//调用所有注册的BeanFactoryPostProcessor的Bean
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
//为BeanFactory注册BeanPost事件处理器.
//BeanPostProcessor是Bean后置处理器，用于监听容器触发的事件
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
//初始化信息源，和国际化相关.
initMessageSource();
// Initialize event multicaster for this context.
//初始化容器事件传播器.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
//调用子类的某些特殊Bean初始化方法
onRefresh();
// Check for listener beans and register them.
//为事件传播器注册事件监听器.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
//初始化所有剩余的单例Bean
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
//初始化容器的生命周期事件处理器，并发布容器的生命周期事件
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.
//销毁已创建的Bean
destroyBeans();
// Reset 'active' flag.
//取消refresh操作，重置容器的同步标识.
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();
}
}
}
跟一下启动的obtainFreshBeanFactory方法。
/**
* Tell the subclass to refresh the internal bean factory.
* @return the fresh BeanFactory instance
* @see #refreshBeanFactory()
* @see #getBeanFactory()
*/
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;
}
...
/**
* Subclasses must implement this method to perform the actual configuration load.
* The method is invoked by {@link #refresh()} before any other initialization work.
* <p>A subclass will either create a new bean factory and hold a reference to it,
* or return a single BeanFactory instance that it holds. In the latter case, it will
* usually throw an IllegalStateException if refreshing the context more than once.
* @throws BeansException if initialization of the bean factory failed
* @throws IllegalStateException if already initialized and multiple refresh
* attempts are not supported
*/
protected abstract void refreshBeanFactory() throws BeansException, IllegalStateException;
refreshBeanFactory是个抽象方法，具体调用的时子类AbstractRefreshableApplicationContext中的refreshBeanFactory
在这个方法中会判断BeanFactory是否已存在，若存在则先销毁beans并关闭beanFactory，接着创建新的IOC容器（DefaultListableBeanFactory），并执行loadBeanDefinitions装载bean定义。
/**
* 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.
*/
@Override
protected final void refreshBeanFactory() throws BeansException {
//如果已经有容器，销毁容器中的bean，关闭容器
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
//创建IOC容器
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
//对IOC容器进行定制化，如设置启动参数，开启注解的自动装配等
customizeBeanFactory(beanFactory);
//调用载入Bean定义的方法，主要这里又使用了一个委派模式，在当前类中只定义了抽象的loadBeanDefinitions方法，具体的实现调用子类容器
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
找到loadBeanDefinitions的具体实现（AbstractXmlApplicationContext中）。
/**
* Loads the bean definitions via an XmlBeanDefinitionReader.
* @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.
//创建XmlBeanDefinitionReader，即创建Bean读取器，并通过回调设置到容器中去，容器使用该读取器读取Bean定义资源
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
//为Bean读取器设置Spring资源加载器，AbstractXmlApplicationContext的
//祖先父类AbstractApplicationContext继承DefaultResourceLoader，因此，容器本身也是一个资源加载器
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
//为Bean读取器设置SAX xml解析器
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
//当Bean读取器读取Bean定义的Xml资源文件时，启用Xml的校验机制
initBeanDefinitionReader(beanDefinitionReader);
//Bean读取器真正实现加载的方法
loadBeanDefinitions(beanDefinitionReader);
}
/**
* Load the bean definitions with the given XmlBeanDefinitionReader.
* <p>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
*/
//Xml Bean读取器加载Bean定义资源
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
//获取Bean定义资源的定位
Resource[] configResources = getConfigResources();
if (configResources != null) {
//Xml Bean读取器调用其父类AbstractBeanDefinitionReader读取定位的Bean定义资源
reader.loadBeanDefinitions(configResources);
}
//如果子类中获取的Bean定义资源定位为空，则获取FileSystemXmlApplicationContext构造方法中setConfigLocations方法设置的资源
String[] configLocations = getConfigLocations();
if (configLocations != null) {
//Xml Bean读取器调用其父类AbstractBeanDefinitionReader读取定位
//的Bean定义资源
reader.loadBeanDefinitions(configLocations);
}
}
/**
* Return an array of Resource objects, referring to the XML bean definition
* files that this context should be built with.
* <p>The default implementation returns {@code null}. Subclasses can override
* this to provide pre-built Resource objects rather than location Strings.
* @return an array of Resource objects, or {@code null} if none
* @see #getConfigLocations()
*/
//这里又使用了一个委派模式，调用子类的获取Bean定义资源定位的方法
//该方法在ClassPathXmlApplicationContext中进行实现
@Nullable
protected Resource[] getConfigResources() {
return null;
}
在AbstractBeanDefinitionReader的loadBeanDefinitions读取Bean定义资源文件
@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;
}
@Override
public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {
return loadBeanDefinitions(location, null);
}
/**
* Load bean definitions from the specified resource location.
* <p>The location can also be a location pattern, provided that the
* ResourceLoader of this bean definition reader is a ResourcePatternResolver.
* @param location the resource location, to be loaded with the ResourceLoader
* (or ResourcePatternResolver) of this bean definition reader
* @param actualResources a Set to be filled with the actual Resource objects
* that have been resolved during the loading process. May be {@code null}
* to indicate that the caller is not interested in those Resource objects.
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
* @see #getResourceLoader()
* @see #loadBeanDefinitions(org.springframework.core.io.Resource)
* @see #loadBeanDefinitions(org.springframework.core.io.Resource[])
*/
public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
//获取在IoC容器初始化过程中设置的资源加载器
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 {
//将指定位置的Bean定义资源文件解析为Spring IOC容器封装的资源
//加载多个指定位置的Bean定义资源文件
Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
//委派调用其子类XmlBeanDefinitionReader的方法，实现加载功能
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.
//将指定位置的Bean定义资源文件解析为Spring IOC容器封装的资源
//加载单个指定位置的Bean定义资源文件
Resource resource = resourceLoader.getResource(location);
//委派调用其子类XmlBeanDefinitionReader的方法，实现加载功能
int loadCount = loadBeanDefinitions(resource);
if (actualResources != null) {
actualResources.add(resource);
}
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
}
return loadCount;
}
}
//重载方法，调用loadBeanDefinitions(String);
@Override
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);
}
return counter;
}
通过resourceLoader.getResource获取资源文件，调用DefaultResourceLoader中的getResource方法
@Override
public Resource getResource(String location) {
Assert.notNull(location, "Location must not be null");
for (ProtocolResolver protocolResolver : this.protocolResolvers) {
Resource resource = protocolResolver.resolve(location, this);
if (resource != null) {
return resource;
}
}
//如果是类路径的方式，那需要使用ClassPathResource 来得到bean 文件的资源对象
if (location.startsWith("/")) {
return getResourceByPath(location);
}
else if (location.startsWith(CLASSPATH_URL_PREFIX)) {
return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader());
}
else {
try {
// Try to parse the location as a URL...
// 如果是URL 方式，使用UrlResource 作为bean 文件的资源对象
URL url = new URL(location);
return (ResourceUtils.isFileURL(url) ? new FileUrlResource(url) : new UrlResource(url));
}
catch (MalformedURLException ex) {
// No URL -> resolve as resource path.
//如果既不是classpath标识，又不是URL标识的Resource定位，则调用
//容器本身的getResourceByPath方法获取Resource
return getResourceByPath(location);
}
}
}
容器本身的getResourceByPath可以参照FileSystemXmlApplicationContext
/**
* Resolve resource paths as file system paths.
* <p>Note: Even if a given path starts with a slash, it will get
* interpreted as relative to the current VM working directory.
* This is consistent with the semantics in a Servlet container.
* @param path path to the resource
* @return Resource handle
* @see org.springframework.web.context.support.XmlWebApplicationContext#getResourceByPath
*/
@Override
protected Resource getResourceByPath(String path) {
if (path.startsWith("/")) {
path = path.substring(1);
}
//这里使用文件系统资源对象来定义bean 文件
return new FileSystemResource(path);
}
<font color="gren">至此第一阶段定位Resource结束</font>
回到XmlBeanDefinitionReader的loadBeanDefinitions
/**
* Load bean definitions from the specified XML file.
* @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
*/
//XmlBeanDefinitionReader加载资源的入口方法
@Override
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
//将读入的XML资源进行特殊编码处理(Resource增强为EncodeResource，装饰器？)
return loadBeanDefinitions(new EncodedResource(resource));
}
/**
* 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
*/
//这里是载入XML形式Bean定义资源文件方法
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<>(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException(
"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
}
try {
//将资源文件转为InputStream的IO流
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
//从InputStream中得到XML的解析源
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
//这里是具体的读取过程
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}
finally {
//关闭从Resource中得到的IO流
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.
* @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
*/
//从特定XML文件中实际载入Bean定义资源的方法
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
//将XML文件转换为DOM对象，解析过程由documentLoader实现
Document doc = doLoadDocument(inputSource, resource);
//这里是启动对Bean定义解析的详细过程，该解析过程会用到Spring的Bean配置规则
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);
}
}
DefaultDocumentLoader
/**
* Load the {@link Document} at the supplied {@link InputSource} using the standard JAXP-configured
* XML parser.
*/
//使用标准的JAXP将载入的Bean定义资源转换成document对象
@Override
public Document loadDocument(InputSource inputSource, EntityResolver entityResolver,
ErrorHandler errorHandler, int validationMode, boolean namespaceAware) throws Exception {
//创建文件解析器工厂
DocumentBuilderFactory factory = createDocumentBuilderFactory(validationMode, namespaceAware);
if (logger.isDebugEnabled()) {
logger.debug("Using JAXP provider [" + factory.getClass().getName() + "]");
}
//创建文档解析器
DocumentBuilder builder = createDocumentBuilder(factory, entityResolver, errorHandler);
//解析Spring的Bean定义资源
return builder.parse(inputSource);
}
/**
* Create the {@link DocumentBuilderFactory} instance.
* @param validationMode the type of validation: {@link XmlValidationModeDetector#VALIDATION_DTD DTD}
* or {@link XmlValidationModeDetector#VALIDATION_XSD XSD})
* @param namespaceAware whether the returned factory is to provide support for XML namespaces
* @return the JAXP DocumentBuilderFactory
* @throws ParserConfigurationException if we failed to build a proper DocumentBuilderFactory
*/
protected DocumentBuilderFactory createDocumentBuilderFactory(int validationMode, boolean namespaceAware)
throws ParserConfigurationException {
//创建文档解析工厂
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(namespaceAware);
//设置解析XML的校验
if (validationMode != XmlValidationModeDetector.VALIDATION_NONE) {
factory.setValidating(true);
if (validationMode == XmlValidationModeDetector.VALIDATION_XSD) {
// Enforce namespace aware for XSD...
factory.setNamespaceAware(true);
try {
factory.setAttribute(SCHEMA_LANGUAGE_ATTRIBUTE, XSD_SCHEMA_LANGUAGE);
}
catch (IllegalArgumentException ex) {
ParserConfigurationException pcex = new ParserConfigurationException(
"Unable to validate using XSD: Your JAXP provider [" + factory +
"] does not support XML Schema. Are you running on Java 1.4 with Apache Crimson? " +
"Upgrade to Apache Xerces (or Java 1.5) for full XSD support.");
pcex.initCause(ex);
throw pcex;
}
}
}
return factory;
}
<font color="gren">至此资源文件由xml解析为Document，之后SpringIOC将会把Document解析为Bean</font>
<font color="gren"> 由资源文件解析而成的Document并不能直接使用，由此开始对Document进行解析</font>
回到XmlBeanDefinitionReader的doLoadBeanDefinitions(InputSource inputSource, Resource resource)
在得到Document后，开始调用registerBeanDefinitions解析
/**
* Register the bean definitions contained in the given DOM document.
* Called by {@code loadBeanDefinitions}.
* <p>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
*/
//按照Spring的Bean语义要求将Bean定义资源解析并转换为容器内部数据结构
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
//得到BeanDefinitionDocumentReader来对xml格式的BeanDefinition解析
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
//获得容器中注册的Bean数量
int countBefore = getRegistry().getBeanDefinitionCount();
//解析过程入口，这里使用了委派模式，BeanDefinitionDocumentReader只是个接口,
//具体的解析实现过程有实现类DefaultBeanDefinitionDocumentReader完成
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
//统计解析的Bean数量
return getRegistry().getBeanDefinitionCount() - countBefore;
}
解析过程在BeanDefinitionDocumentReader的实现类DefaultBeanDefinitionDocumentReader中开始(这里没有像别的地方的代码一样弯弯绕绕，在各种类之间旋转跳跃！感动！)
/**
* This implementation parses bean definitions according to the "spring-beans" XSD
* (or DTD, historically).
* <p>Opens a DOM Document; then initializes the default settings
* specified at the {@code <beans/>} level; then parses the contained bean definitions.
*/
//根据Spring DTD对Bean的定义规则解析Bean定义Document对象
@Override
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
//获得XML描述符
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
//获得Document的根元素
Element root = doc.getDocumentElement();
doRegisterBeanDefinitions(root);
}
/**
* Register each bean definition within the given root {@code <beans/>} element.
*/
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.
//具体的解析过程由BeanDefinitionParserDelegate实现（又一个委派，在BeanDefinitionParserDelegate类中定义了很多bean配置时的参数）
//BeanDefinitionParserDelegate中定义了Spring Bean定义XML文件的各种元素
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;
}
}
}
//在解析Bean定义之前，进行自定义的解析，增强解析过程的可扩展性
//ps:这俩增强解析从来没看到过，是我丢人了
preProcessXml(root);
//从Document的根元素开始进行Bean定义的Document对象
parseBeanDefinitions(root, this.delegate);
//在解析Bean定义之后，进行自定义的解析，增加解析过程的可扩展性
postProcessXml(root);
this.delegate = parent;
}
//创建BeanDefinitionParserDelegate，用于完成真正的解析过程
protected BeanDefinitionParserDelegate createDelegate(
XmlReaderContext readerContext, Element root, @Nullable BeanDefinitionParserDelegate parentDelegate) {
BeanDefinitionParserDelegate delegate = new BeanDefinitionParserDelegate(readerContext);
//BeanDefinitionParserDelegate初始化Document根元素
delegate.initDefaults(root, parentDelegate);
return delegate;
}
/**
* Parse the elements at the root level in the document:
* "import", "alias", "bean".
* @param root the DOM root element of the document
*/
//使用Spring的Bean规则从Document的根元素开始进行Bean定义的Document对象
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
//Bean定义的Document对象使用了Spring默认的XML命名空间
if (delegate.isDefaultNamespace(root)) {
//获取Bean定义的Document对象根元素的所有子节点
NodeList nl = root.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
//获得Document节点是XML元素节点
if (node instanceof Element) {
Element ele = (Element) node;
//Bean定义的Document的元素节点使用的是Spring默认的XML命名空间
if (delegate.isDefaultNamespace(ele)) {
//使用Spring的Bean规则解析元素节点
parseDefaultElement(ele, delegate);
}
else {
//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
delegate.parseCustomElement(ele);
}
}
}
}
else {
//Document的根节点没有使用Spring默认的命名空间，则使用用户自定义的
//解析规则解析Document根节点
delegate.parseCustomElement(root);
}
}
//使用Spring的Bean规则解析Document元素节点
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
//如果元素节点是<Import>导入元素，进行导入解析
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
//如果元素节点是<Alias>别名元素，进行别名解析
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
//元素节点既不是导入元素，也不是别名元素，即普通的<Bean>元素，
//按照Spring的Bean规则解析元素
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}
/**
* Parse an "import" element and load the bean definitions
* from the given resource into the bean factory.
*/
//解析<Import>导入元素，从给定的导入路径加载Bean定义资源到Spring IoC容器中
protected void importBeanDefinitionResource(Element ele) {
//获取给定的导入元素的location属性
String location = ele.getAttribute(RESOURCE_ATTRIBUTE);
//如果导入元素的location属性值为空，则没有导入任何资源，直接返回
if (!StringUtils.hasText(location)) {
getReaderContext().error("Resource location must not be empty", ele);
return;
}
// Resolve system properties: e.g. "${user.dir}"
//使用系统变量值解析location属性值
location = getReaderContext().getEnvironment().resolveRequiredPlaceholders(location);
Set<Resource> actualResources = new LinkedHashSet<>(4);
// Discover whether the location is an absolute or relative URI
//标识给定的导入元素的location是否是绝对路径
boolean absoluteLocation = false;
try {
absoluteLocation = ResourcePatternUtils.isUrl(location) || ResourceUtils.toURI(location).isAbsolute();
}
catch (URISyntaxException ex) {
// cannot convert to an URI, considering the location relative
// unless it is the well-known Spring prefix "classpath*:"
//给定的导入元素的location不是绝对路径
}
// Absolute or relative?
//给定的导入元素的location是绝对路径
if (absoluteLocation) {
try {
//使用资源读入器加载给定路径的Bean定义资源
int importCount = getReaderContext().getReader().loadBeanDefinitions(location, actualResources);
if (logger.isDebugEnabled()) {
logger.debug("Imported " + importCount + " bean definitions from URL location [" + location + "]");
}
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error(
"Failed to import bean definitions from URL location [" + location + "]", ele, ex);
}
}
else {
// No URL -> considering resource location as relative to the current file.
//给定的导入元素的location是相对路径
try {
int importCount;
//将给定导入元素的location封装为相对路径资源
Resource relativeResource = getReaderContext().getResource().createRelative(location);
//封装的相对路径资源存在
if (relativeResource.exists()) {
//使用资源读入器加载Bean定义资源
importCount = getReaderContext().getReader().loadBeanDefinitions(relativeResource);
actualResources.add(relativeResource);
}
//封装的相对路径资源不存在
else {
//获取Spring IOC容器资源读入器的基本路径
String baseLocation = getReaderContext().getResource().getURL().toString();
//根据Spring IOC容器资源读入器的基本路径加载给定导入路径的资源
importCount = getReaderContext().getReader().loadBeanDefinitions(
StringUtils.applyRelativePath(baseLocation, location), actualResources);
}
if (logger.isDebugEnabled()) {
logger.debug("Imported " + importCount + " bean definitions from relative location [" + location + "]");
}
}
catch (IOException ex) {
getReaderContext().error("Failed to resolve current resource location", ele, ex);
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to import bean definitions from relative location [" + location + "]",
ele, ex);
}
}
Resource[] actResArray = actualResources.toArray(new Resource[actualResources.size()]);
//在解析完<Import>元素之后，发送容器导入其他资源处理完成事件
getReaderContext().fireImportProcessed(location, actResArray, extractSource(ele));
}
/**
* Process the given alias element, registering the alias with the registry.
*/
//解析<Alias>别名元素，为Bean向Spring IoC容器注册别名
protected void processAliasRegistration(Element ele) {
//获取<Alias>别名元素中name的属性值
String name = ele.getAttribute(NAME_ATTRIBUTE);
//获取<Alias>别名元素中alias的属性值
String alias = ele.getAttribute(ALIAS_ATTRIBUTE);
boolean valid = true;
//<alias>别名元素的name属性值为空
if (!StringUtils.hasText(name)) {
getReaderContext().error("Name must not be empty", ele);
valid = false;
}
//<alias>别名元素的alias属性值为空
if (!StringUtils.hasText(alias)) {
getReaderContext().error("Alias must not be empty", ele);
valid = false;
}
if (valid) {
try {
//向容器的资源读入器注册别名
//进去看一下，目前看的比较粗略
getReaderContext().getRegistry().registerAlias(name, alias);
}
catch (Exception ex) {
getReaderContext().error("Failed to register alias '" + alias +
"' for bean with name '" + name + "'", ele, ex);
}
//在解析完<Alias>元素之后，发送容器别名处理完成事件
getReaderContext().fireAliasRegistered(name, alias, extractSource(ele));
}
}
/**
* Process the given bean element, parsing the bean definition
* and registering it with the registry.
*/
//解析Bean定义资源Document对象的普通元素
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
// 开始普通元素的解析
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
// BeanDefinitionHolder是对BeanDefinition的封装，即Bean定义的封装类
//对Document对象中<Bean>元素的解析由BeanDefinitionParserDelegate实现
// BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// Register the final decorated instance.
//向Spring IOC容器注册解析得到的Bean定义，这是Bean定义向IOC容器注册的入口
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// Send registration event.
//在完成向Spring IOC容器注册解析得到的Bean定义之后，发送注册事件
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
/**
* Allow the XML to be extensible by processing any custom element types first,
* before we start to process the bean definitions. This method is a natural
* extension point for any other custom pre-processing of the XML.
* <p>The default implementation is empty. Subclasses can override this method to
* convert custom elements into standard Spring bean definitions, for example.
* Implementors have access to the parser's bean definition reader and the
* underlying XML resource, through the corresponding accessors.
* @see #getReaderContext()
*/
protected void preProcessXml(Element root) {
}
/**
* Allow the XML to be extensible by processing any custom element types last,
* after we finished processing the bean definitions. This method is a natural
* extension point for any other custom post-processing of the XML.
* <p>The default implementation is empty. Subclasses can override this method to
* convert custom elements into standard Spring bean definitions, for example.
* Implementors have access to the parser's bean definition reader and the
* underlying XML resource, through the corresponding accessors.
* @see #getReaderContext()
*/
protected void postProcessXml(Element root) {
}
import和alias的元素都在本类中完成解析，并发送容器处理完成事件,其他类型元素，即普通的<bean>元素则由BeanDefinitionParserDelegate解析
/**
* 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}.
*/
//解析<Bean>元素的入口
@Nullable
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}.
*/
//解析Bean定义资源文件中的<Bean>元素，这个方法中主要处理<Bean>元素的id，name和别名属性
@Nullable
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
//获取<Bean>元素中的id属性值
String id = ele.getAttribute(ID_ATTRIBUTE);
//获取<Bean>元素中的name属性值
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
//获取<Bean>元素中的alias属性值
List<String> aliases = new ArrayList<>();
//将<Bean>元素中的所有name属性值存放到别名中
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
aliases.addAll(Arrays.asList(nameArr));
}
String beanName = id;
//如果<Bean>元素中没有配置id属性时，将别名中的第一个值赋值给beanName
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");
}
}
//检查<Bean>元素所配置的id或者name的唯一性，containingBean标识<Bean>
//元素中是否包含子<Bean>元素
if (containingBean == null) {
//检查<Bean>元素所配置的id、name或者别名是否重复
checkNameUniqueness(beanName, aliases, ele);
}
//详细对<Bean>元素中配置的Bean定义进行解析的地方
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
if (beanDefinition != null) {
if (!StringUtils.hasText(beanName)) {
try {
if (containingBean != null) {
//如果<Bean>元素中没有配置id、别名或者name，且没有包含子元素
//<Bean>元素，为解析的Bean生成一个唯一beanName并注册
beanName = BeanDefinitionReaderUtils.generateBeanName(
beanDefinition, this.readerContext.getRegistry(), true);
}
else {
//如果<Bean>元素中没有配置id、别名或者name，且包含了子元素
//<Bean>元素，为解析的Bean生成一个别名以便后续向IOC容器注册
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.
//为解析的Bean使用别名注册时，为了向后兼容
//Spring1.2/2.0，给别名添加类名后缀
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);
}
//当解析出错时，返回null
return null;
}
/**
* Parse the bean definition itself, without regard to name or aliases. May return
* {@code null} if problems occurred during the parsing of the bean definition.
*/
//详细对<Bean>元素中配置的Bean定义其他属性进行解析
//由于上面的方法中已经对Bean的id、name和别名等属性进行了处理
//该方法中主要处理除这三个以外的其他属性数据
//ps:此处没有实例化bean，只是将bean的配置信息载入BeanDefinition，以供后续实例化时使用
@Nullable
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, @Nullable BeanDefinition containingBean) {
//记录解析的<Bean>
this.parseState.push(new BeanEntry(beanName));
String className = null;
//这里只读取<Bean>元素中配置的class名字，然后载入到BeanDefinition中去
//只是记录配置的class名字，不做实例化，对象的实例化在依赖注入时完成
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
String parent = null;
//如果<Bean>元素中配置了parent属性，则获取parent属性的值
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
try {
//根据<Bean>元素配置的class名称和parent属性值创建BeanDefinition
//为载入Bean定义信息做准备
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
//对当前的<Bean>元素中配置的一些属性进行解析和设置，如配置的单态(singleton)属性等
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
//为<Bean>元素解析的Bean设置description信息
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
//对<Bean>元素的meta(元信息)属性解析
parseMetaElements(ele, bd);
//对<Bean>元素的lookup-method属性解析
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
//对<Bean>元素的replaced-method属性解析
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
//解析<Bean>元素的构造方法设置
parseConstructorArgElements(ele, bd);
//解析<Bean>元素的<property>设置
parsePropertyElements(ele, bd);
//解析<Bean>元素的qualifier属性
parseQualifierElements(ele, bd);
//为当前解析的Bean设置所需的资源和依赖对象
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();
}
//解析<Bean>元素出错时，返回null
return null;
}
以<property>的解析为例
/**
* Parse property sub-elements of the given bean element.
*/
//解析<Bean>元素中的<property>子元素
public void parsePropertyElements(Element beanEle, BeanDefinition bd) {
//获取<Bean>元素中所有的子元素
NodeList nl = beanEle.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
//如果子元素是<property>子元素，则调用解析<property>子元素方法解析
if (isCandidateElement(node) && nodeNameEquals(node, PROPERTY_ELEMENT)) {
parsePropertyElement((Element) node, bd);
}
}
}
/**
* Parse a property element.
*/
//解析<property>元素
public void parsePropertyElement(Element ele, BeanDefinition bd) {
//获取<property>元素的名字
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 {
//如果一个Bean中已经有同名的property存在，则不进行解析，直接返回。
//即如果在同一个Bean中配置同名的property，则只有第一个起作用
if (bd.getPropertyValues().contains(propertyName)) {
error("Multiple 'property' definitions for property '" + propertyName + "'", ele);
return;
}
//解析获取property的值
Object val = parsePropertyValue(ele, bd, propertyName);
//根据property的名字和值创建property实例
PropertyValue pv = new PropertyValue(propertyName, val);
//解析<property>元素中的属性
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.
*/
//解析获取property值
@Nullable
public Object parsePropertyValue(Element ele, BeanDefinition bd, @Nullable String propertyName) {
String elementName = (propertyName != null) ?
"<property> element for property '" + propertyName + "'" :
"<constructor-arg> element";
// Should only have one child element: ref, value, list, etc.
//获取<property>的所有子元素，只能是其中一种类型:ref,value,list,etc等
NodeList nl = ele.getChildNodes();
Element subElement = null;
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
//子元素不是description和meta属性
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 {
//当前<property>元素包含有子元素
subElement = (Element) node;
}
}
}
//判断property的属性值是ref还是value，不允许既是ref又是value
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);
}
//如果属性是ref，创建一个ref的数据对象RuntimeBeanReference
//这个对象封装了ref信息
if (hasRefAttribute) {
String refName = ele.getAttribute(REF_ATTRIBUTE);
if (!StringUtils.hasText(refName)) {
error(elementName + " contains empty 'ref' attribute", ele);
}
//一个指向运行时所依赖对象的引用
RuntimeBeanReference ref = new RuntimeBeanReference(refName);
//设置这个ref的数据对象是被当前的property对象所引用
ref.setSource(extractSource(ele));
return ref;
}
//如果属性是value，创建一个value的数据对象TypedStringValue
//这个对象封装了value信息
else if (hasValueAttribute) {
//一个持有String类型值的对象
TypedStringValue valueHolder = new TypedStringValue(ele.getAttribute(VALUE_ATTRIBUTE));
//设置这个value数据对象是被当前的property对象所引用
valueHolder.setSource(extractSource(ele));
return valueHolder;
}
//如果当前<property>元素还有子元素
else if (subElement != null) {
//解析<property>的子元素
return parsePropertySubElement(subElement, bd);
}
else {
// Neither child element nor "ref" or "value" attribute found.
//propery属性中既不是ref，也不是value属性，解析出错返回null
error(elementName + " must specify a ref or value", ele);
return null;
}
}
如上
ref 被封装为指向依赖对象的引用
-
value 被封装为持有value字符串值的对象
最后都通过 setSource 关联起来
当<property>还有子元素时，解析子元素
/**
* 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
*/
//解析<property>元素中ref,value或者集合等子元素
@Nullable
public Object parsePropertySubElement(Element ele, @Nullable BeanDefinition bd, @Nullable String defaultValueType) {
//如果<property>没有使用Spring默认的命名空间，则使用用户自定义的规则解析内嵌元素
if (!isDefaultNamespace(ele)) {
return parseNestedCustomElement(ele, bd);
}
//如果子元素是bean，则使用解析<Bean>元素的方法解析
else if (nodeNameEquals(ele, BEAN_ELEMENT)) {
BeanDefinitionHolder nestedBd = parseBeanDefinitionElement(ele, bd);
if (nestedBd != null) {
nestedBd = decorateBeanDefinitionIfRequired(ele, nestedBd, bd);
}
return nestedBd;
}
//如果子元素是ref，ref中只能有以下3个属性：bean、local、parent
else if (nodeNameEquals(ele, REF_ELEMENT)) {
// A generic reference to any name of any bean.
//可以不再同一个Spring配置文件中，具体请参考Spring对ref的配置规则
String refName = ele.getAttribute(BEAN_REF_ATTRIBUTE);
boolean toParent = false;
if (!StringUtils.hasLength(refName)) {
// A reference to the id of another bean in a parent context.
//获取<property>元素中parent属性值，引用父级容器中的Bean
refName = ele.getAttribute(PARENT_REF_ATTRIBUTE);
toParent = true;
if (!StringUtils.hasLength(refName)) {
error("'bean' or 'parent' is required for <ref> element", ele);
return null;
}
}
if (!StringUtils.hasText(refName)) {
error("<ref> element contains empty target attribute", ele);
return null;
}
//创建ref类型数据，指向被引用的对象
RuntimeBeanReference ref = new RuntimeBeanReference(refName, toParent);
//设置引用类型值是被当前子元素所引用
ref.setSource(extractSource(ele));
return ref;
}
//如果子元素是<idref>，使用解析ref元素的方法解析
else if (nodeNameEquals(ele, IDREF_ELEMENT)) {
return parseIdRefElement(ele);
}
//如果子元素是<value>，使用解析value元素的方法解析
else if (nodeNameEquals(ele, VALUE_ELEMENT)) {
return parseValueElement(ele, defaultValueType);
}
//如果子元素是null，为<property>设置一个封装null值的字符串数据
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;
}
//如果子元素是<array>，使用解析array集合子元素的方法解析
else if (nodeNameEquals(ele, ARRAY_ELEMENT)) {
return parseArrayElement(ele, bd);
}
//如果子元素是<list>，使用解析list集合子元素的方法解析
else if (nodeNameEquals(ele, LIST_ELEMENT)) {
return parseListElement(ele, bd);
}
//如果子元素是<set>，使用解析set集合子元素的方法解析
else if (nodeNameEquals(ele, SET_ELEMENT)) {
return parseSetElement(ele, bd);
}
//如果子元素是<map>，使用解析map集合子元素的方法解析
else if (nodeNameEquals(ele, MAP_ELEMENT)) {
return parseMapElement(ele, bd);
}
//如果子元素是<props>，使用解析props集合子元素的方法解析
else if (nodeNameEquals(ele, PROPS_ELEMENT)) {
return parsePropsElement(ele);
}
//既不是ref，又不是value，也不是集合，则子元素配置错误，返回null
else {
error("Unknown property sub-element: [" + ele.getNodeName() + "]", ele);
return null;
}
}
子元素具体解析以List为例
/**
* Parse a list element.
*/
//解析<list>集合子元素
public List<Object> parseListElement(Element collectionEle, @Nullable BeanDefinition bd) {
//获取<list>元素中的value-type属性，即获取集合元素的数据类型
String defaultElementType = collectionEle.getAttribute(VALUE_TYPE_ATTRIBUTE);
//获取<list>集合元素中的所有子节点
NodeList nl = collectionEle.getChildNodes();
//Spring中将List封装为ManagedList
ManagedList<Object> target = new ManagedList<>(nl.getLength());
target.setSource(extractSource(collectionEle));
//设置集合目标数据类型
target.setElementTypeName(defaultElementType);
target.setMergeEnabled(parseMergeAttribute(collectionEle));
//具体的<list>元素解析
parseCollectionElements(nl, target, bd, defaultElementType);
return target;
}
//具体解析<list>集合元素，<array>、<list>和<set>都使用该方法解析
protected void parseCollectionElements(
NodeList elementNodes, Collection<Object> target, @Nullable BeanDefinition bd, String defaultElementType) {
//遍历集合所有节点
for (int i = 0; i < elementNodes.getLength(); i++) {
Node node = elementNodes.item(i);
//节点不是description节点
if (node instanceof Element && !nodeNameEquals(node, DESCRIPTION_ELEMENT)) {
//将解析的元素加入集合中，递归调用下一个子元素
target.add(parsePropertySubElement((Element) node, bd, defaultElementType));
}
}
}
<font color='gren'>经过上述步骤的解析，资源文件中的Document对象解析为BeanDefinition。</font><font color="red">但是还没有将这些Bean定义信息注册到 IOC 容器中。</font>
回到刚才进行解析的地方（DefaultBeanDefinitionDocumentReader 中的processBeanDefinition)继续往下
/**
* Process the given bean element, parsing the bean definition
* and registering it with the registry.
*/
//解析Bean定义资源Document对象的普通元素
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
// 开始普通元素的解析
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
// BeanDefinitionHolder是对BeanDefinition的封装，即Bean定义的封装类
//对Document对象中<Bean>元素的解析由BeanDefinitionParserDelegate实现
// BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
//---------------解析得到bdHolder------------------
try {
// Register the final decorated instance.
//向Spring IOC容器注册解析得到的Bean定义，这是Bean定义向IOC容器注册的入口
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// Send registration event.
//在完成向Spring IOC容器注册解析得到的Bean定义之后，发送注册事件
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
/**
* Register the given bean definition with the given bean factory.
* @param definitionHolder the bean definition including name and aliases
* @param registry the bean factory to register with
* @throws BeanDefinitionStoreException if registration failed
*/
//将解析的BeanDefinitionHold注册到容器中
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
// Register bean definition under primary name.
//获取解析的BeanDefinition的名称
String beanName = definitionHolder.getBeanName();
//向IOC容器注册BeanDefinition
//到DefaultListableBeanFactory的对应方法中~
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
// Register aliases for bean name, if any.
//如果解析的BeanDefinition有别名，向容器为其注册别名
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias);
}
}
}
实际调用DefaultListableBeanFactory中的方法进行注册，把注册的bean信息放在一个ConcurrentHashMap中
/** Map of bean definition objects, keyed by bean name */
//存储注册信息的BeanDefinition
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);
//---------------------------------------------------------------------
// Implementation of BeanDefinitionRegistry interface
//---------------------------------------------------------------------
//向IOC容器注册解析的BeanDefiniton
@Override
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
throws BeanDefinitionStoreException {
Assert.hasText(beanName, "Bean name must not be empty");
Assert.notNull(beanDefinition, "BeanDefinition must not be null");
//校验解析的BeanDefiniton
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
BeanDefinition oldBeanDefinition;
oldBeanDefinition = this.beanDefinitionMap.get(beanName);
// 存在旧值，考虑是否允许覆盖
if (oldBeanDefinition != null) {
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
"': There is already [" + oldBeanDefinition + "] bound.");
}
else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (this.logger.isWarnEnabled()) {
this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +
"' with a framework-generated bean definition: replacing [" +
oldBeanDefinition + "] with [" + beanDefinition + "]");
}
}
else if (!beanDefinition.equals(oldBeanDefinition)) {
if (this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
//过了前面一系列验证，覆盖老的重名bean
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
if (hasBeanCreationStarted()) {
// Cannot modify startup-time collection elements anymore (for stable iteration)
// 注册的过程中需要线程同步，以保证数据的一致性
// 锁一个concurrentHashMap的意义在哪？讲道理和其他地方有联动，暂时看不出来...
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
//如果单例模式的bean名单中有该bean的name，那么移除掉它。
//也就是说着，将一个原本是单例模式的bean重新注册成一个普通的bean
if (this.manualSingletonNames.contains(beanName)) {
Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
}
else {
// Still in startup registration phase
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}
//检查是否有同名的BeanDefinition已经在IOC容器中注册
if (oldBeanDefinition != null || containsSingleton(beanName)) {
//重置所有已经注册过的BeanDefinition的缓存
resetBeanDefinition(beanName);
}
}
<font color="red">注册结束，资源文件中的Bean相关信息载入到 IOC 容器中。 IOC 容器初始化完成</font>
回顾一下容器初始化的大致流程：
定位找到资源文件，并将资源文件载入->解析资源文件，把文件解析成为Document->将解析后的Document再次解析，成为容器能识别的Bean信息->把Bean信息注册到容器中
关于BeanFactory 和 FactoryBean 的区别这边略过。
初看源码，虽然是跟着已有的教程走的，感觉还是不够深入。蛮多地方还是心存疑问的。希望在看完后续的源码后再回头能有新的理解。
同时也再次认识到——真！的！好！菜！啊！
