【spring5源码分析】IoC部分

定位阶段

​ 1. 构造器中初始化。

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public ClassPathXmlApplicationContext(
String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
throws BeansException {

super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}
  1. 调用 setConfigLocations(),解析定义资源文件的路径,将其保存到字符串数组。
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//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;
}
}
  1. 调用 refresh(),启动容器。
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@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
//1、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.
//2、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.
//3、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.
//4、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.
//5、调用所有注册的BeanFactoryPostProcessor的Bean
invokeBeanFactoryPostProcessors(beanFactory);

// Register bean processors that intercept bean creation.
//6、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.
//7、初始化信息源,和国际化相关.
initMessageSource();

// Initialize event multicaster for this context.
//8、初始化容器事件传播器.
initApplicationEventMulticaster();

// Initialize other special beans in specific context subclasses.
//9、调用子类的某些特殊Bean初始化方法
onRefresh();

// Check for listener beans and register them.
//10、为事件传播器注册事件监听器.
registerListeners();

// Instantiate all remaining (non-lazy-init) singletons.
//11、初始化所有剩余的单例Bean
finishBeanFactoryInitialization(beanFactory);

// Last step: publish corresponding event.
//12、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.
//13、销毁已创建的Bean
destroyBeans();

// Reset 'active' flag.
//14、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...
//15、重设公共缓存
resetCommonCaches();
}
}
}
  1. 在 refresh() 中,调用 AbstractApplicationContext 类的 obtainFreshBeanFactory() 方法。
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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;
}
  1. 使用委派模式,在子类中调用 refreshBeanFactory() 方法,启动beanFactory。
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@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);
}
}
加载阶段
  1. 使用委派模式,调用 loadBeanDefinitions() 方法。
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//实现父类抽象的载入Bean定义方法
@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);
}
  1. 调用自己的 loadBeanDefinitions() 方法。
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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);
}
}
  1. 调用 AbstractBeanDefinitionReader 类的 loadBeanDefinitions() 方法。
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@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;
}
  1. 调用 XmlBeanDefinitionReader 类的 loadBeanDefinitions() 方法。
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//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();
}
}
}
  1. 调用自己的 doLoadBeanDefinitions() 方法。
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//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);
}
}
  1. 调用自己的 registerBeanDefinitions() 方法。
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//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;
}
  1. 调用 DefaultBeanDefinitionDocumentReader 类的 registerBeanDefinitions() 方法,根据Spring DTD对Bean的定义规则解析Bean定义Document对象。
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@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);
}
  1. 调用自己的 doRegisterBeanDefinitions() 方法。注册beanDefinition。
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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,
//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
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;
}
注册阶段
  1. 调用 DefaultBeanDefinitionDocumentReader 类的 parseBeanDefinitions() 方法。
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/**
* 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) {
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));
}
}
  1. 调用 BeanDefinitionReaderUtils 的 registerBeanDefinition() 方法,将解析的BeanDefinitionHold注册到容器中。
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//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
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);
}
}
}
  1. 向IoC容器注册BeanDefinition,将注册信息存入beanDefinitionMap 中
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//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);

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 + "]");
}
}
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
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;
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);
}
}


The End.