This article brings you an introduction to the Spring-IOC container (with code). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.
The loading of Bean definition resources by the Spring IoC container starts from the refresh() function. refresh() is a template method. The function of the refresh() method is: before creating the IoC container, if there is already If the container exists, you need to destroy and close the existing container to ensure that the newly established IoC container is used after refresh. The function of refresh is similar to restarting the IoC container. It initializes the container in the newly created container and loads the Bean definition resources.
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 Class:
AbstractRefreshableApplicationContext only defines abstract ones loadBeanDefinitions method, what the container actually calls is the implementation of this method by its subclass AbstractXmlApplicationContext
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 Class:
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;
}The loading process is defined in its abstract parent class AbstractBeanDefinitionReader
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);
}
}
}
}Specific method of loading resources
First, call the resource loader's resource acquisition method resourceLoader.getResource(location) to obtain the resource to be loaded.
Secondly, the actual loading function is the loadBeanDefinitions method of its subclass XmlBeanDefinitionReader.
The resource location ends here. What is finally returned is a Resource object for loading BeanDefinition. After the positioning is completed, the maker I/O conditions are loaded for the BeanDefinition,
but the specific loading has not yet started.
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);
}The loading of BeanDefinition is divided into two parts. First, the document object is obtained through the XML parser.
But these document objects are not parsed according to spring's Bean rules. After XML parsing is completed, it is parsed according to Spring's Bean rules. This parsing process is implemented in documentReader.
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);
}
}
}
}Convert the xml file into a document object and then parse the BeanDefinition
Here is the method of loading the Bean definition resource file in XML form
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 container based on The located Bean definition resource file is loaded, read and converted into a Document object. The process is completed.
The following is how the Spring IoC container converts the loaded Bean definition resource file into a Document object, then parses it into a Spring IoC managed Bean object and registers it in the container
@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 parses the document object and converts it into BeanDefinition according to the definition rules of spring Bean
@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) {
}
}As can be seen from the above Spring IoC container parsing the loaded Bean definition Document, we When using Spring, you can use the
For elements that are neither
The following is the parsing process for the Bean element
//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;
}Through the analysis of the above source code, you will understand that the attributes we configure in the
Note: During the process of parsing the
In the above method, some of the parsing of some configurations such as meta information (meta), qualifier, etc. are not used much when configuring in Spring. When we use Spring's
Call the registerBeanDefinition method of BeanDefinitionReaderUtils to register the parsed Bean with the IoC container
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));
}
}When calling BeanDefinitionReaderUtils to register the parsed BeanDefinition with the IoC container, it is the DefaultListableBeanFactory that actually completes the registration function.
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 method
//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);
}
}At this point, after the beans configured in the Bean definition resource file have been parsed, they have been registered in the IoC container and managed by the container, truly completing the IoC container initialization. All the work done. Now the entire Bean configuration information has been established in the IoC container. This BeanDefinition information is already available and can be retrieved. The role of the IoC container is to process and maintain these registered Bean definition information. These registered Bean definition information are the basis for IoC container inversion of control. It is with these registered data that the container can perform dependency injection.
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