Spring容器的初始化流程
一、創建BeanFactory流程
1、流程入口
創建BeanFactory的流程是從refresh方法的第二步開始的,通過調用obtainFreshBeanFactory方法完成流程。
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
2、流程分析
創建BeanFactory的流程是從第二步開始的,調用AbstractApplicationContext類中的obtainFreshBeanFactory方法:
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() { // 主要是通過該方法完成IoC容器的刷新 refreshBeanFactory(); ConfigurableListableBeanFactory beanFactory = getBeanFactory(); if (logger.isDebugEnabled()) { logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory); } return beanFactory; }
調用AbstractRefreshableApplicationContext中的refreshBeanFactory方法:
protected final void refreshBeanFactory() throws BeansException { // 如果之前有IoC容器,則銷毀 if (hasBeanFactory()) { destroyBeans(); closeBeanFactory(); } try { // 創建IoC容器,也就是DefaultListableBeanFactory DefaultListableBeanFactory beanFactory = createBeanFactory(); beanFactory.setSerializationId(getId()); // 設置工廠的屬性:是否允許BeanDefinition覆蓋和是否允許循環依賴 customizeBeanFactory(beanFactory); // 調用載入BeanDefinition的方法,在當前類中只定義了抽象的loadBeanDefinitions方法,具體的實現調用子類容器 loadBeanDefinitions(beanFactory); synchronized (this.beanFactoryMonitor) { this.beanFactory = beanFactory; } } catch (IOException ex) { throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex); } }
其中調用createBeanFactory方法創建IoC容器。這裏創建的是DefaultListableBeanFactory,它是真正用於管理Bean實例及BeanDefeation的工廠。
二、加載BeanDefeation流程
1、流程入口
此流程是從AbstractRefreshableApplicationContext的refreshBeanFactory方法開始的,代碼如上所示,通過loadBeanDefinitions(beanFactory)
進行BeanDefeation的加載。
loadBeanDefinitions(beanFactory);
2、流程圖
這裏的調用較為復雜,可通過下面流程圖進行說明:
3、流程分析
在創建完Ioc容器之後,調用AbstractXmlApplicationContext的loadBeanDefinitions進行beanDefeation的加載,其代碼如下:
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// 創建一個BeanDefinition閱讀器,通過閱讀XML文件,真正完成BeanDefinition的加載和註冊
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
initBeanDefinitionReader(beanDefinitionReader);
// 委托給BeanDefinition閱讀器去加載BeanDefinition
loadBeanDefinitions(beanDefinitionReader);
}
再調用其重載方法loadBeanDefinitions,代碼如下:
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
// 獲取資源的定位
// 這裏getConfigResources是一個空實現,真正實現是調用子類的獲取資源定位的方法
// 比如:ClassPathXmlApplicationContext中進行了實現,而FileSystemXmlApplicationContext沒有使用該方法
Resource[] configResources = getConfigResources();
if (configResources != null) {
// XML Bean讀取器調用其父類AbstractBeanDefinitionReader讀取定位的資源
reader.loadBeanDefinitions(configResources);
}
// 如果子類中獲取的資源定位為空,則獲取FileSystemXmlApplicationContext構造方法中setConfigLocations方法設置的資源
String[] configLocations = getConfigLocations();
if (configLocations != null) {
// XML Bean讀取器調用其父類AbstractBeanDefinitionReader讀取定位的資源
reader.loadBeanDefinitions(configLocations);
}
}
再調用的方法,代碼如下:
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
// 將讀入的XML資源進行特殊編碼處理
return loadBeanDefinitions(new EncodedResource(resource));
}
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 {
// 將資源文件轉為InputStream的IO流
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
// 從InputStream中得到XML的解析源
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
// 這裏是具體的讀取過程
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}
finally {
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();
}
}
}
具體的讀取過程在doLoadBeanDefinitions方法中進行,將讀取的beanDefinition信息進行註冊:
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
// 通過DOM4J加載解析XML文件,最終形成Document對象
Document doc = doLoadDocument(inputSource, resource);
// 通過對Document對象的操作,完成BeanDefinition的加載和註冊工作
return registerBeanDefinitions(doc, resource);
}
//拋出異常。。。
}
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
// 創建BeanDefinitionDocumentReader來解析Document對象,完成BeanDefinition解析
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
// 獲得容器中已經註冊的BeanDefinition數量
int countBefore = getRegistry().getBeanDefinitionCount();
//解析過程入口,BeanDefinitionDocumentReader只是個接口,具體的實現過程在DefaultBeanDefinitionDocumentReader完成
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
// 統計新的的BeanDefinition數量
return getRegistry().getBeanDefinitionCount() - countBefore;
}
在上面的registerBeanDefinitions方法中,關註兩個方法:
createReaderContext(),主要用於獲取NameSpaceResolver
registerBeanDefinitions(),通過獲取的獲取NameSpaceResolver查找對應的NameSpaceHandler,解析文檔,得到BeanDefinition,並進行註冊。
註:這裏是通過/src/main/resources/META-INF/spring.handlers文件進行匹配的
首先查看createReaderContext方法:
public XmlReaderContext createReaderContext(Resource resource) {
return new XmlReaderContext(resource, this.problemReporter, this.eventListener, this.sourceExtractor, this, getNamespaceHandlerResolver());
}
public NamespaceHandlerResolver getNamespaceHandlerResolver() {
if (this.namespaceHandlerResolver == null) {
this.namespaceHandlerResolver = createDefaultNamespaceHandlerResolver();
}
return this.namespaceHandlerResolver;
}
protected NamespaceHandlerResolver createDefaultNamespaceHandlerResolver() {
ClassLoader cl = (getResourceLoader() != null ? getResourceLoader().getClassLoader() : getBeanClassLoader());
return new DefaultNamespaceHandlerResolver(cl);
}
通過這三個方法,將NamespaceHandlerResolver初始化成功。
再查看DefaultBeanDefinitionDocumentReader的registerBeanDefinitions方法,代碼如下:
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
// 獲得Document的根元素<beans>標簽
Element root = doc.getDocumentElement();
// 真正實現BeanDefinition解析和註冊工作
doRegisterBeanDefinitions(root);
}
這裏的doRegisterBeanDefinitions是真正進行BeanDefinition解析和註冊工作的。
protected void doRegisterBeanDefinitions(Element root) {
// 這裏使用了委托模式,將具體的BeanDefinition解析工作交給了BeanDefinitionParserDelegate去完成
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = createDelegate(getReaderContext(), root, parent);
// 判斷該根標簽是否包含http://www.springframework.org/schema/beans默認命名空間
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定義之前,進行自定義的解析,增強解析過程的可擴展性
preProcessXml(root);
// 委托給BeanDefinitionParserDelegate,從Document的根元素開始進行BeanDefinition的解析
parseBeanDefinitions(root, this.delegate);
// 在解析Bean定義之後,進行自定義的解析,增加解析過程的可擴展性
postProcessXml(root);
this.delegate = parent;
}
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
// 加載的Document對象是否使用了Spring默認的XML命名空間(beans命名空間)
if (delegate.isDefaultNamespace(root)) {
// 獲取Document對象根元素的所有子節點(bean標簽、import標簽、alias標簽和其他自定義標簽context、aop等)
NodeList nl = root.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (node instanceof Element) {
Element ele = (Element) node;
// bean標簽、import標簽、alias標簽,則使用默認解析規則
if (delegate.isDefaultNamespace(ele)) {
parseDefaultElement(ele, delegate);
}
else {//像context標簽、aop標簽、tx標簽,則使用用戶自定義的解析規則解析元素節點
delegate.parseCustomElement(ele);
}
}
}
}
else {
// 如果不是默認的命名空間,則使用用戶自定義的解析規則解析元素節點
delegate.parseCustomElement(root);
}
}
這裏根據是否默認的命名空間和標簽進行不同的處理,我們先關註默認的處理。
如下,在parseDefaultElement中進行默認標簽的解析:
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
// 解析<import>標簽
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
// 解析<alias>標簽
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
// 解析<bean>標簽
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
// 解析內置<bean>標簽
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// 遞歸調用
doRegisterBeanDefinitions(ele);
}
}
這裏重點關註一下bean標簽的解析,如上,調用processBeanDefinition方法。
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
// 解析<bean>標簽,獲取BeanDefinition
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
// 如果需要,則裝飾BeanDefinition對象
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// Register the final decorated instance.
// 註冊最終的BeanDefinition到BeanDefinitionRegistry(DefaultListableBeanFactory)
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name ‘" +
bdHolder.getBeanName() + "‘", ele, ex);
}
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
這裏通過對bean的解析獲取BeanDefinition對象,並對其進行裝飾,最終將BeanDefinition註冊到DefaultListableBeanFactory中,通過Map集合的方式進行存儲。
這裏調用BeanDefinitionParserDelegate中的三個重載方法parseBeanDefinitionElement方法進行bean標簽的解析,代碼如下:
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) {
// 解析<bean>標簽,獲取BeanDefinition對象
return parseBeanDefinitionElement(ele, null);
}
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
// 獲取bean的id
String id = ele.getAttribute(ID_ATTRIBUTE);
// 獲取bean的name
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
List<String> aliases = new ArrayList<>();
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
aliases.addAll(Arrays.asList(nameArr));
}
String beanName = id;
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");
}
}
if (containingBean == null) {
// 檢查bean的id或者name是否唯一
checkNameUniqueness(beanName, aliases, ele);
}
// 解析<bean>標簽,獲取BeanDefinition對象
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
if (beanDefinition != null) {
if (!StringUtils.hasText(beanName)) {
try {
if (containingBean != null) {
beanName = BeanDefinitionReaderUtils.generateBeanName(
beanDefinition, this.readerContext.getRegistry(), true);
}
else {
beanName = this.readerContext.generateBeanName(beanDefinition);
String beanClassName = beanDefinition.getBeanClassName();
if (beanClassName != null &&
beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
!this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
aliases.add(beanClassName);
}
}
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);
// 將BeanDefinition對象和BeanName封裝到BeanDefinitionHolder對象中
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}
return null;
}
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, @Nullable BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
String className = null;
// 獲取bean標簽的class屬性
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
String parent = null;
// 獲取bean標簽的parent屬性
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
try {
// 創建BeanDefinition對象GenericBeanDefinition
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
// 解析<bean>標簽的屬性
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
/** 解析<bean>標簽的子標簽 --- begin**/
// 解析<description>標簽
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
// 解析<meta>標簽
parseMetaElements(ele, bd);
// 解析<lookup-method>標簽
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
// 解析<replaced-method>標簽
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
// 解析<constructor-arg>標簽
parseConstructorArgElements(ele, bd);
// 解析<property>標簽
parsePropertyElements(ele, bd);
// 解析<qualifier>標簽
parseQualifierElements(ele, bd);
/** 解析<bean>標簽的子標簽 --- end**/
bd.setResource(this.readerContext.getResource());
bd.setSource(extractSource(ele));
return bd;
}
//拋出異常。。。
return null;
}
三、創建Bean流程
1、流程入口
創建Bean的流程是refresh方法中的第11步:
// 實例化剩余的單例bean(非懶加載方式)
// 註意事項:Bean的IoC、DI和AOP都是發生在此步驟
finishBeanFactoryInitialization(beanFactory);
2、流程圖
sequenceDiagram AbstractApplicationContext->>DefaultListableBeanFactory:preInstantiateSingletons DefaultListableBeanFactory->>AbstractBeanFactory:getBean AbstractBeanFactory->>AbstractBeanFactory:doGetBean AbstractBeanFactory->>AbstractAutowireCapableBeanFactory:createBean AbstractAutowireCapableBeanFactory->>AbstractAutowireCapableBeanFactory:doCreateBean3、流程分析
首先通過finishBeanFactoryInitialization方法,進入DefaultListableBeanFactory的preInstantiateSingletons方法中,代碼如下:
public void preInstantiateSingletons() throws BeansException {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Pre-instantiating singletons in " + this);
}
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// 觸發所有非懶加載方式的單例bean的創建
for (String beanName : beanNames) {
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
// 如果bean不是抽象的,而且是單例的,同時還不是懶加載的,則進行下面的操作
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
// 如果bean是一個工廠bean,則走下面的方法
if (isFactoryBean(beanName)) {
Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
if (bean instanceof FactoryBean) {
final FactoryBean<?> factory = (FactoryBean<?>) bean;
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>)
((SmartFactoryBean<?>) factory)::isEagerInit,
getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
}
else { // 普通bean走下面的方法
getBean(beanName);
}
}
}
這裏主要關註普通bean的創建,進入AbstractBeanFactory中的getBean方法:
public Object getBean(String name) throws BeansException {
// 獲取Bean的實例
return doGetBean(name, null, null, false);
}
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType, @Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
// 獲取bean名稱
final String beanName = transformedBeanName(name);
Object bean;
// 從緩存中獲取單例bean
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) { //如果獲取到單例bean,則走下面代碼
if (logger.isDebugEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
logger.debug("Returning eagerly cached instance of singleton bean ‘" + beanName +
"‘ that is not fully initialized yet - a consequence of a circular reference");
}
else {
logger.debug("Returning cached instance of singleton bean ‘" + beanName + "‘");
}
}
// 如果取出來的Bean實例是FactoryBean的Bean實例,則需要從FactoryBean實例中產生一個對象實例。
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {//如果沒有獲取到單例bean,則走下面代碼
// 如果原型模式的Bean發生循環引用,則直接不處理,拋出異常
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory.
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {
return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
nameToLookup, requiredType, args, typeCheckOnly);
}
else if (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
}
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
try {
// 獲取要實例化的bean的BeanDefinition對象
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
// 檢查該BeanDefinition對象對應的Bean是否是抽象的
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dep : dependsOn) {
if (isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between ‘" + beanName + "‘ and ‘" + dep + "‘");
}
registerDependentBean(dep, beanName);
try {
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"‘" + beanName + "‘ depends on missing bean ‘" + dep + "‘", ex);
}
}
}
// 如果是單例的Bean,請下面的代碼
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, () -> {
try {
// 創建單例Bean的主要方法
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
destroySingleton(beanName);
throw ex;
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
else if (mbd.isPrototype()) {
// It‘s a prototype -> create a new instance.
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {
String scopeName = mbd.getScope();
final Scope scope = this.scopes.get(scopeName);
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope name ‘" + scopeName + "‘");
}
try {
Object scopedInstance = scope.get(beanName, () -> {
beforePrototypeCreation(beanName);
try {
return createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
});
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
catch (IllegalStateException ex) {
throw new BeanCreationException(beanName,
"Scope ‘" + scopeName + "‘ is not active for the current thread; consider " +
"defining a scoped proxy for this bean if you intend to refer to it from a singleton",
ex);
}
}
}
catch (BeansException ex) {
cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
}
這裏主要關註單例Bean的的創建,進入AbstractAutowireCapableBeanFactory中的createBean方法,跳轉到doCreateBean方法中,這裏是進行bean創建的核心代碼:
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
if (logger.isDebugEnabled()) {
logger.debug("Creating instance of bean ‘" + beanName + "‘");
}
RootBeanDefinition mbdToUse = mbd;
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
// Prepare method overrides.
// 處理方法覆蓋
try {
mbdToUse.prepareMethodOverrides();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
beanName, "Validation of method overrides failed", ex);
}
try {
// 獲取BeanPostProcessor代理對象
Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
if (bean != null) {
return bean;
}
}
catch (Throwable ex) {
throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
"BeanPostProcessor before instantiation of bean failed", ex);
}
try {
// 完成Bean實例的創建(實例化、填充屬性、初始化)
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isDebugEnabled()) {
logger.debug("Finished creating instance of bean ‘" + beanName + "‘");
}
return beanInstance;
}
catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
throw ex;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
}
}
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
// bean初始化第一步:默認調用無參構造實例化Bean
// 構造參數依賴註入,就是發生在這一步
if (instanceWrapper == null) {
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
// 實例化後的Bean對象
final Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
// Allow post-processors to modify the merged bean definition.
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}
// 解決循環依賴的關鍵步驟
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences && isSingletonCurrentlyInCreation(beanName));
// 如果需要提前暴露單例Bean,則將該Bean放入三級緩存中
if (earlySingletonExposure) {
if (logger.isDebugEnabled()) {
logger.debug("Eagerly caching bean ‘" + beanName + "‘ to allow for resolving potential circular references");
}
// 將剛創建的bean放入三級緩存中singleFactories(key是beanName,value是FactoryBean)
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
// bean初始化第二步:填充屬性(DI依賴註入發生在此步驟)
populateBean(beanName, mbd, instanceWrapper);
// bean初始化第三步:調用初始化方法,完成bean的初始化操作(AOP發生在此步驟)
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
catch (Throwable ex) {
if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
throw (BeanCreationException) ex;
}
else {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
}
}
if (earlySingletonExposure) {
Object earlySingletonReference = getSingleton(beanName, false);
if (earlySingletonReference != null) {
if (exposedObject == bean) {
exposedObject = earlySingletonReference;
}
else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
String[] dependentBeans = getDependentBeans(beanName);
Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
for (String dependentBean : dependentBeans) {
if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
actualDependentBeans.add(dependentBean);
}
}
if (!actualDependentBeans.isEmpty()) {
throw new BeanCurrentlyInCreationException(beanName, "...");
}
}
}
}
// Register bean as disposable.
try {
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}
這裏通過三步實現Bean的創建,具體的實現會再後面文章進行說明。
Spring容器的初始化流程