这篇文章将为大家详细讲解有关Java中Spring-IOC容器是什么，小编觉得挺实用的，因此分享给大家做个参考，希望大家阅读完这篇文章后可以有所收获。
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
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public void refresh() throws BeansException, IllegalStateException {
Object var1 = this.startupShutdownMonitor;
synchronized(this.startupShutdownMonitor) {
//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
this.prepareRefresh();
//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
//这个bean的载入过程 包括对xml的解析和加载为BeanDefinitions 都是从this.obtainFreshBeanFactory()这里进入
ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
/*这之后的代码都是注册容器的信息源和生命周期事件*/
//为BeanFactory配置容器特性，例如类加载器、事件处理器等
this.prepareBeanFactory(beanFactory);
try {
//为容器的某些子类指定特殊的BeanPost事件处理器
this.postProcessBeanFactory(beanFactory);
//调用所有注册的BeanFactoryPostProcessor的Bean
this.invokeBeanFactoryPostProcessors(beanFactory);
//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
this.registerBeanPostProcessors(beanFactory);
//初始化信息源，和国际化相关.
this.initMessageSource();
//初始化容器事件传播器.
this.initApplicationEventMulticaster();
//调用子类的某些特殊Bean初始化方法
this.onRefresh();
//为事件传播器注册事件监听器.
this.registerListeners();
//初始化所有剩余的单态Bean.
this.finishBeanFactoryInitialization(beanFactory);
//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
this.finishRefresh();
} catch (BeansException var9) {
if (this.logger.isWarnEnabled()) {
this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var9);
}
//销毁以创建的单态Bean
this.destroyBeans();
//取消refresh操作，重置容器的同步标识.
this.cancelRefresh(var9);
throw var9;
} finally {
this.resetCommonCaches();
}
}
}AbstractRefreshableApplicationContext 类：
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
protected final void refreshBeanFactory() throws BeansException {
//如果已经创建了BeanFactory，则销毁并关闭BeanFactory
if (this.hasBeanFactory()) {
this.destroyBeans();
this.closeBeanFactory();
}
try {
//创建了一个IOC容器
DefaultListableBeanFactory beanFactory = this.createBeanFactory();
beanFactory.setSerializationId(this.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
this.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
this.loadBeanDefinitions(beanFactory);
Object var2 = this.beanFactoryMonitor;
synchronized(this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
} catch (IOException var5) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + this.getDisplayName(), var5);
}
}AbstractXmlApplicationContext 类：
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
//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);
beanDefinitionReader.setEnvironment(this.getEnvironment());
//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.setResourceLoader(this);
//为Bean读取器设置SAX xml解析器
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
//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
this.initBeanDefinitionReader(beanDefinitionReader);
//Bean读取器真正实现加载的方法
this.loadBeanDefinitions(beanDefinitionReader);
}
protected void initBeanDefinitionReader(XmlBeanDefinitionReader reader) {
reader.setValidating(this.validating);
}
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
Resource[] configResources = this.getConfigResources();
if (configResources != null) {
reader.loadBeanDefinitions(configResources);
}
String[] configLocations = this.getConfigLocations();
if (configLocations != null) {
reader.loadBeanDefinitions(configLocations);
}
}
@Nullable
protected Resource[] getConfigResources() {
return null;
}在其抽象父类AbstractBeanDefinitionReader中定义了载入过程
public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
//获取resourceLoader
ResourceLoader resourceLoader = this.getResourceLoader();
if (resourceLoader == null) {
throw new BeanDefinitionStoreException("Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
} else {
int loadCount;
if (!(resourceLoader instanceof ResourcePatternResolver)) {
//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 完成具体的资源定位的工作
Resource resource = resourceLoader.getResource(location);
//加载资源 开始我们的第二步操作 转换为BeanDefinition对象
loadCount = this.loadBeanDefinitions((Resource)resource);
if (actualResources != null) {
actualResources.add(resource);
}
if (this.logger.isDebugEnabled()) {
this.logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
}
return loadCount;
} else {
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
//加载单个指定位置的Bean定义资源文件
Resource[] resources = ((ResourcePatternResolver)resourceLoader).getResources(location);
//加载资源 开始我们的第二步操作 转换为BeanDefinition对象
loadCount = this.loadBeanDefinitions(resources);
if (actualResources != null) {
Resource[] var6 = resources;
int var7 = resources.length;
for(int var8 = 0; var8 < var7; ++var8) {
Resource resource = var6[var8];
actualResources.add(resource);
}
}
if (this.logger.isDebugEnabled()) {
this.logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
}
return loadCount;
} catch (IOException var10) {
throw new BeanDefinitionStoreException("Could not resolve bean definition resource pattern [" + location + "]", var10);
}
}
}
}具体加载资源的方法
首先，调用资源加载器的获取资源方法resourceLoader.getResource(location)，获取到要加载的资源。
其次，真正执行加载功能是其子类XmlBeanDefinitionReader的loadBeanDefinitions方法。
资源定位到这里就结束 最终返回的是一个Resource的对象来进行BeanDefinition的载入。在定位完成后,为BeanDefinition的载入创客I/O条件，
但是具体的载入还没有开始载入。
public Resource getResource(String location) {
Assert.notNull(location, "Location must not be null");
Iterator var2 = this.protocolResolvers.iterator();
Resource resource;
do {
if (!var2.hasNext()) {
//处理/开头的定位
if (location.startsWith("/")) {
return this.getResourceByPath(location);
}
//带有classpath标识的Resource
if (location.startsWith("classpath:")) {
return new ClassPathResource(location.substring("classpath:".length()), this.getClassLoader());
}
try {
//处理URL标识的Resource定位
URL url = new URL(location);
return (Resource)(ResourceUtils.isFileURL(url) ? new FileUrlResource(url) : new UrlResource(url));
} catch (MalformedURLException var5) {
//如果不存classpath、Url、/标志的 就教给他处理
return this.getResourceByPath(location);
}
}
ProtocolResolver protocolResolver = (ProtocolResolver)var2.next();
resource = protocolResolver.resolve(location, this);
} while(resource == null);
return resource;
}protected Resource getResourceByPath(String path) {
if (path != null && 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);
}BeanDefinition的载入分成两部分,首先通过XML的解析器得到document对象，
但这些document对象没有按照spring的Bean规则进行解析。在完成XML解析后，才是按照Spring的Bean规则进行解析，这个解析的过程是在documentReader实现。
public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
//获取resourceLoader
ResourceLoader resourceLoader = this.getResourceLoader();
if (resourceLoader == null) {
throw new BeanDefinitionStoreException("Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
} else {
int loadCount;
if (!(resourceLoader instanceof ResourcePatternResolver)) {
//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 完成具体的资源定位的工作
Resource resource = resourceLoader.getResource(location);
//加载资源 开始我们的第二步操作 转换为BeanDefinition对象
loadCount = this.loadBeanDefinitions((Resource)resource);
if (actualResources != null) {
actualResources.add(resource);
}
if (this.logger.isDebugEnabled()) {
this.logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
}
return loadCount;
} else {
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
//加载单个指定位置的Bean定义资源文件
Resource[] resources = ((ResourcePatternResolver)resourceLoader).getResources(location);
//加载资源 开始我们的第二步操作 转换为BeanDefinition对象
loadCount = this.loadBeanDefinitions(resources);
if (actualResources != null) {
Resource[] var6 = resources;
int var7 = resources.length;
for(int var8 = 0; var8 < var7; ++var8) {
Resource resource = var6[var8];
actualResources.add(resource);
}
}
if (this.logger.isDebugEnabled()) {
this.logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
}
return loadCount;
} catch (IOException var10) {
throw new BeanDefinitionStoreException("Could not resolve bean definition resource pattern [" + location + "]", var10);
}
}
}
}xml文件转换为document对象 再解析BeanDefinition
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(this.logger.isInfoEnabled()) {
this.logger.info("Loading XML bean definitions from " + encodedResource.getResource());
}
Set<EncodedResource> currentResources = (Set)this.resourcesCurrentlyBeingLoaded.get();
if(currentResources == null) {
currentResources = new HashSet(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if(!((Set)currentResources).add(encodedResource)) {
throw new BeanDefinitionStoreException("Detected cyclic loading of " + encodedResource + " - check your import definitions!");
} else {
int var5;
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
var5 = this.doLoadBeanDefinitions(inputSource, encodedResource.getResource());
} finally {
//IO流的关闭
inputStream.close();
}
} catch (IOException var15) {
throw new BeanDefinitionStoreException("IOException parsing XML document from " + encodedResource.getResource(), var15);
} finally {
((Set)currentResources).remove(encodedResource);
if(((Set)currentResources).isEmpty()) {
this.resourcesCurrentlyBeingLoaded.remove();
}
}
return var5;
}
} protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException {
try {
//@1将XML文件转换为DOM对象，解析过程由documentLoader实现
Document doc = this.doLoadDocument(inputSource, resource);
//@2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 this.registerBeanDefinitions(doc, resource);
} catch (BeanDefinitionStoreException var4) {
throw var4;
} catch (SAXParseException var5) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(), "Line " + var5.getLineNumber() + " in XML document from " + resource + " is invalid", var5);
} catch (SAXException var6) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(), "XML document from " + resource + " is invalid", var6);
} catch (ParserConfigurationException var7) {
throw new BeanDefinitionStoreException(resource.getDescription(), "Parser configuration exception parsing XML from " + resource, var7);
} catch (IOException var8) {
throw new BeanDefinitionStoreException(resource.getDescription(), "IOException parsing XML document from " + resource, var8);
} catch (Throwable var9) {
throw new BeanDefinitionStoreException(resource.getDescription(), "Unexpected exception parsing XML document from " + resource, var9);
}
}@1
//使用标准的JAXP将载入的Bean定义资源转换成document对象
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 = this.createDocumentBuilderFactory(validationMode, namespaceAware);
if(logger.isDebugEnabled()) {
logger.debug("Using JAXP provider [" + factory.getClass().getName() + "]");
}
//创建文档解析器
DocumentBuilder builder = this.createDocumentBuilder(factory, entityResolver, errorHandler);
//解析Spring的Bean定义资源
return builder.parse(inputSource);
}
protected DocumentBuilderFactory createDocumentBuilderFactory(int validationMode, boolean namespaceAware) throws ParserConfigurationException {
//创建文档解析工厂
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(namespaceAware);
if(validationMode != 0) {
//设置解析XML的校验
factory.setValidating(true);
if(validationMode == 3) {
factory.setNamespaceAware(true);
try {
factory.setAttribute("http://java.sun.com/xml/jaxp/properties/schemaLanguage", "http://www.w3.org/2001/XMLSchema");
} catch (IllegalArgumentException var6) {
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(var6);
throw pcex;
}
}
}
return factory;
}Spring IoC容器根据定位的Bean定义资源文件，将其加载读入并转换成为Document对象过程完成。
下面是 Spring IoC容器将载入的Bean定义资源文件转换为Document对象之后，是如何将其解析为Spring IoC管理的Bean对象并将其注册到容器中的
@2
//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 = this.createBeanDefinitionDocumentReader();
//获得容器中注册的Bean数量
int countBefore = this.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
//@1
documentReader.registerBeanDefinitions(doc, this.createReaderContext(resource));
/统计解析的Bean数量
return this.getRegistry().getBeanDefinitionCount() - countBefore;
}
//创建BeanDefinitionDocumentReader对象，解析Document对象
protected BeanDefinitionDocumentReader createBeanDefinitionDocumentReader() {
return (BeanDefinitionDocumentReader)BeanDefinitionDocumentReader.class.cast(BeanUtils.instantiateClass(this.documentReaderClass));
}DefaultBeanDefinitionDocumentReader 解析document对象按照spring Bean的定义规则转换为BeanDefinition
@1
public class DefaultBeanDefinitionDocumentReader implements BeanDefinitionDocumentReader {
public static final String BEAN_ELEMENT = "bean";
public static final String NESTED_BEANS_ELEMENT = "beans";
public static final String ALIAS_ELEMENT = "alias";
public static final String NAME_ATTRIBUTE = "name";
public static final String ALIAS_ATTRIBUTE = "alias";
public static final String IMPORT_ELEMENT = "import";
public static final String RESOURCE_ATTRIBUTE = "resource";
public static final String PROFILE_ATTRIBUTE = "profile";
protected final Log logger = LogFactory.getLog(this.getClass());
private XmlReaderContext readerContext;
private BeanDefinitionParserDelegate delegate;
public DefaultBeanDefinitionDocumentReader() {
}
//根据Spring DTD对Bean的定义规则解析Bean定义Document对象
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
//获得XML描述符
this.readerContext = readerContext;
this.logger.debug("Loading bean definitions");
//获得Document的根元素
Element root = doc.getDocumentElement();
this.doRegisterBeanDefinitions(root);
}
protected final XmlReaderContext getReaderContext() {
return this.readerContext;
}
protected Object extractSource(Element ele) {
return this.getReaderContext().extractSource(ele);
}
//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
protected void doRegisterBeanDefinitions(Element root) {
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = this.createDelegate(this.getReaderContext(), root, parent);
if(this.delegate.isDefaultNamespace(root)) {
String profileSpec = root.getAttribute("profile");
if(StringUtils.hasText(profileSpec)) {
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(profileSpec, ",; ");
if(!this.getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
if(this.logger.isInfoEnabled()) {
this.logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec + "] not matching: " + this.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
this.preProcessXml(root);
//从Document的根元素开始进行Bean定义的Document对象
this.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
this.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, BeanDefinitionParserDelegate parentDelegate) {
BeanDefinitionParserDelegate delegate = new BeanDefinitionParserDelegate(readerContext);
//BeanDefinitionParserDelegate初始化Document根元素
delegate.initDefaults(root, parentDelegate);
return delegate;
}
//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
this.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);
}
}
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")) {
this.importBeanDefinitionResource(ele);
} else if(delegate.nodeNameEquals(ele, "alias")) {
//如果元素节点是<Alias>别名元素，进行别名解析
this.processAliasRegistration(ele);
} else if(delegate.nodeNameEquals(ele, "bean")) {
//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
this.processBeanDefinition(ele, delegate);
} else if(delegate.nodeNameEquals(ele, "beans")) {
//如果元素节点是<beans>元素注册为BeanDefintion
this.doRegisterBeanDefinitions(ele);
}
}
//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");
if(!StringUtils.hasText(location)) {
this.getReaderContext().error("Resource location must not be empty", ele);
} else {
//获取location的值
location = this.getReaderContext().getEnvironment().resolveRequiredPlaceholders(location);
Set<Resource> actualResources = new LinkedHashSet(4);
//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 var11) {
;
}
int importCount;
if(absoluteLocation) {
try {
//使用资源读入器加载给定路径的Bean定义资源
importCount = this.getReaderContext().getReader().loadBeanDefinitions(location, actualResources);
if(this.logger.isDebugEnabled()) {
this.logger.debug("Imported " + importCount + " bean definitions from URL location [" + location + "]");
}
} catch (BeanDefinitionStoreException var10) {
this.getReaderContext().error("Failed to import bean definitions from URL location [" + location + "]", ele, var10);
}
} else {
//给定的导入元素的location是相对路径
try {
Resource relativeResource = this.getReaderContext().getResource().createRelative(location);
if(relativeResource.exists()) {
//使用资源读入器加载Bean定义资源
importCount = this.getReaderContext().getReader().loadBeanDefinitions(relativeResource);
actualResources.add(relativeResource);
} else {
String baseLocation = this.getReaderContext().getResource().getURL().toString();
importCount = this.getReaderContext().getReader().loadBeanDefinitions(StringUtils.applyRelativePath(baseLocation, location), actualResources);
}
if(this.logger.isDebugEnabled()) {
this.logger.debug("Imported " + importCount + " bean definitions from relative location [" + location + "]");
}
} catch (IOException var8) {
this.getReaderContext().error("Failed to resolve current resource location", ele, var8);
} catch (BeanDefinitionStoreException var9) {
this.getReaderContext().error("Failed to import bean definitions from relative location [" + location + "]", ele, var9);
}
}
//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
Resource[] actResArray = (Resource[])actualResources.toArray(new Resource[actualResources.size()]);
this.getReaderContext().fireImportProcessed(location, actResArray, this.extractSource(ele));
}
}
//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");
//获取<Alias>别名元素中alias的属性值
String alias = ele.getAttribute("alias");
boolean valid = true;
if(!StringUtils.hasText(name)) {
this.getReaderContext().error("Name must not be empty", ele);
valid = false;
}
if(!StringUtils.hasText(alias)) {
this.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
this.getReaderContext().getRegistry().registerAlias(name, alias);
} catch (Exception var6) {
this.getReaderContext().error("Failed to register alias '" + alias + "' for bean with name '" + name + "'", ele, var6);
}
//在解析完<Alias>元素之后，发送容器别名处理完成事件
this.getReaderContext().fireAliasRegistered(name, alias, this.extractSource(ele));
}
}
//解析Bean定义资源Document对象的普通元素
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
// 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);
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if(bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
//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, this.getReaderContext().getRegistry());
} catch (BeanDefinitionStoreException var5) {
this.getReaderContext().error("Failed to register bean definition with name '" + bdHolder.getBeanName() + "'", ele, var5);
}
//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
this.getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
protected void preProcessXml(Element root) {
}
protected void postProcessXml(Element root) {
}
}通过上述Spring IoC容器对载入的Bean定义Document解析可以看出，我们使用Spring时，在Spring配置文件中可以使用<Import>元素来导入IoC容器所需要的其他资源，Spring IoC容器在解析时会首先将指定导入的资源加载进容器中。使用<Ailas>别名时，Spring IoC容器首先将别名元素所定义的别名注册到容器中。
对于既不是<Import>元素，又不是<Alias>元素的元素，即Spring配置文件中普通的<Bean>元素的解析由BeanDefinitionParserDelegate类的parseBeanDefinitionElement方法来实现。
下面是针对对Bean元素的解析过程
//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
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
//获取id属性
String id = ele.getAttribute("id");
//获取name属性
String nameAttr = ele.getAttribute("name");
List<String> aliases = new ArrayList();
//将Bean元素的name属性全部放到alias属性里面
if(StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, ",; ");
aliases.addAll(Arrays.asList(nameArr));
}
String beanName = id;
if(!StringUtils.hasText(id) && !aliases.isEmpty()) {
beanName = (String)aliases.remove(0);
if(this.logger.isDebugEnabled()) {
this.logger.debug("No XML 'id' specified - using '" + beanName + "' as bean name and " + aliases + " as aliases");
}
}
if(containingBean == null) {
//检查bean元素的id和name是否是唯一的
this.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 = this.parseBeanDefinitionElement(ele, beanName, containingBean);
if(beanDefinition != null) {
if(!StringUtils.hasText(beanName)) {
try {
if(containingBean != null) {
//判断如果没有id和name属性时候是否包含子元素的<Bean>
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//<Bean>元素，为解析的Bean使用别名向IoC容器注册
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);
}
}
if(this.logger.isDebugEnabled()) {
this.logger.debug("Neither XML 'id' nor 'name' specified - using generated bean name [" + beanName + "]");
}
} catch (Exception var9) {
this.error(var9.getMessage(), ele);
return null;
}
}
String[] aliasesArray = StringUtils.toStringArray(aliases);
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
} else {
return null;
}
}
//详细解析bean元素的地方
public AbstractBeanDefinition parseBeanDefinitionElement(Element ele, String beanName, BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
String className = null;
//是否包含class属性
if(ele.hasAttribute("class")) {
//获取class属性值 不做实例化，bean的实例化是在第一次获取bean的时候完成，这里只获取class的值
className = ele.getAttribute("class").trim();
}
try {
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")) {
parent = ele.getAttribute("parent");
}
//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 = this.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
this.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));
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, "description"));
//对<Bean>元素的meta(元信息)属性解析
this.parseMetaElements(ele, bd);
//对<Bean>元素的lookup-method属性解析
this.parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
//对<Bean>元素的replaced-method属性解析
this.parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
//解析<Bean>元素的构造方法设置
this.parseConstructorArgElements(ele, bd);
//解析<Bean>元素的<property>设置
this.parsePropertyElements(ele, bd);
//解析<Bean>元素的qualifier属性
this.parseQualifierElements(ele, bd);
bd.setResource(this.readerContext.getResource());
bd.setSource(this.extractSource(ele));
AbstractBeanDefinition var7 = bd;
return var7;
} catch (ClassNotFoundException var13) {
this.error("Bean class [" + className + "] not found", ele, var13);
} catch (NoClassDefFoundError var14) {
this.error("Class that bean class [" + className + "] depends on not found", ele, var14);
} catch (Throwable var15) {
this.error("Unexpected failure during bean definition parsing", ele, var15);
} finally {
this.parseState.pop();
}
return null;
}通过对上述源码的分析，就会明白我们在Spring配置文件中<Bean>元素的中配置的属性就是通过该方法解析和设置到Bean中去的。
注意：在解析<Bean>元素过程中没有创建和实例化Bean对象，只是创建了Bean对象的定义类BeanDefinition，将<Bean>元素中的配置信息设置到BeanDefinition中作为记录，当依赖注入时才使用这些记录信息创建和实例化具体的Bean对象。
上面方法中一些对一些配置如元信息(meta)、qualifier等的解析，我们在Spring中配置时使用的也不多，我们在使用Spring的<Bean>元素时，配置最多的是<property>属性。
调用BeanDefinitionReaderUtils的registerBeanDefinition方法向IoC容器注册解析的Bean
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if(bdHolder != null) {
//通过对document对象的解析和封装返回一个BeanDefinitionHolder
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
//通过这个holder来注册bean对象
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, this.getReaderContext().getRegistry());
} catch (BeanDefinitionStoreException var5) {
this.getReaderContext().error("Failed to register bean definition with name '" + bdHolder.getBeanName() + "'", ele, var5);
}
this.getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}当调用BeanDefinitionReaderUtils向IoC容器注册解析的BeanDefinition时，真正完成注册功能的是DefaultListableBeanFactory。
public static void registerBeanDefinition(BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry) throws BeanDefinitionStoreException {
String beanName = definitionHolder.getBeanName();
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
String[] aliases = definitionHolder.getAliases();
if(aliases != null) {
String[] var4 = aliases;
int var5 = aliases.length;
for(int var6 = 0; var6 < var5; ++var6) {
String alias = var4[var6];
registry.registerAlias(beanName, alias);
}
}
}DefaultListableBeanFactory registerBeanDefinition方法
//存储注册的俄BeanDefinition
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap(256);
//向IoC容器注册解析的BeanDefiniton
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 var9) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", var9);
}
}
BeanDefinition oldBeanDefinition = (BeanDefinition)this.beanDefinitionMap.get(beanName);
if(oldBeanDefinition != null) {
if(!this.isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName + "': There is already [" + oldBeanDefinition + "] bound.");
}
if(oldBeanDefinition.getRole() < beanDefinition.getRole()) {
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(this.hasBeanCreationStarted()) {
Map var4 = this.beanDefinitionMap;
//注册的过程中需要线程同步，以保证数据的一致性
synchronized(this.beanDefinitionMap) {
//把bean存放到map中
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 {
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if(oldBeanDefinition != null || this.containsSingleton(beanName)) {
this.resetBeanDefinition(beanName);
}
}至此，Bean定义资源文件中配置的Bean被解析过后，已经注册到IoC容器中，被容器管理起来，真正完成了IoC容器初始化所做的全部工作。现 在IoC容器中已经建立了整个Bean的配置信息，这些BeanDefinition信息已经可以使用，并且可以被检索，IoC容器的作用就是对这些注册的Bean定义信息进行处理和维护。这些的注册的Bean定义信息是IoC容器控制反转的基础，正是有了这些注册的数据，容器才可以进行依赖注入。
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