Spring Core -- IOC原始碼解析
阿新 • • 發佈:2019-12-31
這篇文章主要對Core包中的流程進行梳理,註解。
其中包括各個主要類之間的聯絡,以及對實現Bean解析的Refresh()、createBean()、getBean()方法的剖析。
Core包中類關係
refresh方法解析
@Override
public void refresh() throws BeansException,IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
//準備所有需要初始化的資源
// 1. 設定開始時間
// 2. 初始化配置檔案 -- 空實現,預設不作處理
// 3. 新增環境中沒有的配置
// 4. 儲存應用監聽器
// 5. 初始化earlyApplicationEvents,在multicaster可用時釋出事件
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
// 1. 銷燬所有單例Beans,關閉當前工廠
// 2. 新建DefaultListableBeanFactory工廠並設定
// 3. loadBeanDefinitions方法載入BeanDefinitions到工廠
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
// 1. 讓工廠使用環境類的類載入器,新增Spring EL解析器,新增配置編輯器註冊商(其為PropertyEditor註冊器陣列,它的職責是用來註冊PropertyEditor,而PropertyEditor可以定義如何解析配置,比如將2019-08-18解析成java.util.date.class)
// 2. 新增ApplicationContextAwareProcessor到工廠,主要用於在bean建立時,例項化後,初始化前,檢查bean上是否實現了某個Aware介面,有的話做相應呼叫。
// 3. 忽略EnvironmentAware、EmbeddedValueResolverAware、ResourceLoaderAware、ApplicationEventPublisherAware、MessageSourceAware、ApplicationContextAware介面自動注入的依賴。這裡解釋一下為什麼要忽略這些注入:Spring自動建立Bean,但Bean是無狀態的,也就是說Bean不知道Spring容器BeanFactory的任何資訊,包括Bean自己的名稱name,Spring這樣做的目的是為了Spring容器和Bean的解耦。那麼如果Bean要想定製化的做一些操作,就必須要獲取BeanFactory中的資訊,在Spring Bean的生命週期中我們都知道實現一些列介面去觀察Bean建立過程中的一些資訊。所以我們在建立Bean的過程中通過實現一些介面的方式去獲取BeanDefinition資訊。但這裡我們需要正常例項化一個Bean並不需要去拿到這些資訊,所以忽略掉這些介面。
// 4. 建立一些沒有註冊到工廠中的自動裝配Bean對映關聯關係(BeanFactory、ResourceLoader、ApplicationEventPublisher、ApplicationContext) 即:有些物件並不在BeanFactory中,但是我們依然想讓它們可以被裝配。
// 5. 新增ApplicationListenerDetector到工廠,用於探測是應用監聽器的內部Bean
// 6. 判斷是否包含了類載入時期的程式碼織入(AspectJ)。包含則新增LoadTimeWeaverAwareProcessor(用於給LoadTimeWeaverAware Bean新增loadTimeWeaver類)到工廠
// 7. 不存在則註冊環境、系統配置、系統環境Bean到工廠
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
// 允許子類在所有的bean尚未初始化之前註冊BeanPostProcessor,空實現且沒有子類覆蓋。
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
// 允許我們在bean正式初始化之前改變其值。有兩種方式:
// 通過程式碼的方式:context.addBeanFactoryPostProcessor
// 通過xml配置的方式:<bean class="base.SimpleBeanFactoryPostProcessor" />
// 具體怎麼實現的這裡不贅訴了,主要原始碼在PostProcessorRegistrationDelegate中,通過使用BeanFactory的getBeanNamesForType方法獲取相應的BeanDefinition的name陣列,之後逐一呼叫getBean方法獲取到bean(初始化),這裡有一個優先順序的概念,如果你的BeanFactoryPostProcessor同時實現了Ordered或者是PriorityOrdered介面,那麼會被首先執行。下面registerBeanPostProcessors也是一樣的
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
// 簡述一下就是在BeanDefinitions中尋找BeanPostProcessor,之後呼叫BeanFactory.addBeanPostProcessor方法儲存在一個List中,新增的時侯有優先順序的概念,優先順序高的在前面。
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
// 初始化國際化資源
// 1. 如果工廠包含messageSource Bean,就呼叫getBean方法完成其初始化並將其儲存在AbstractApplicationContext內部messageSource成員變數中,用來處理getMessage呼叫。此處使用了委託模式。
// 2. 如果沒有配置此bean,那麼初始化一個DelegatingMessageSource物件,使用一個空實現用以處理getMessage呼叫請求。
initMessageSource();
// Initialize event multicaster for this context.
// 1. 在BeanFactory中尋找ApplicationEventMulticaster的bean,如果找到,那麼呼叫getBean方法將其初始化,同樣這裡將applicationEventMulticaster儲存在變數中,並使用委託模式來處理呼叫publishEvent時,對委託物件的multicastEvent方法的間接呼叫。
// 2. 如果找不到那麼使用SimpleApplicationEventMulticaster。
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
// 模版方法,允許子類在進行bean初始化之前進行一些定製操作。預設空實現。
onRefresh();
// Check for listener beans and register them.
// 1. 新增當前AbstractAppContext環境的應用監聽器到ApplicationEventMulticaster中
// 2. 儲存所有Bean名稱到AbstractApplicationEventMulticaster內部類istenerRetriever.applicationListenerBeans屬性中
// 3. 釋出early application events,如果不為空
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
// 1. 如果包含conversionService Bean那麼就設定ConversionService(其作用和PropertyEditor一致都是轉換用)到工廠
// 2. 如果不包含embeddedValueResolver(用於解析註解的值),設定預設值
// 3. 初始化LoadTimeWeaverAware Bean,用以能完成轉譯類
// 4. 停止使用臨時類載入器,凍結且快取工廠配置不允許修改,
// 5. 初始化所有預載入的單例Bean
// 1. 通過beanDefinitionNames遍歷beans
// 2. 如果當前遍歷的bean不是抽象、不是懶載入、是單例的那麼就判斷當前bean是否是FactoryBean,如果是就給每個bean加上字首“&”,並通過getBean初始化bean,如果此bean是FactoryBean型別還是SmartFactoryBean型別,那麼需要判斷是否需要eagerInit馬上進行初始化。
// 3. 如果當前bean不是FactoryBean,就直接呼叫getBean進行初始化
// 4. 待遍歷所有bean初始化完成後還需要遍歷所有是SmartInitializingSingleton型別的bean來觸發該型別介面的afterSingletonsInstantiated方法。(這裡的應用場景主要是在所有單例 bean 建立完成之後,可以在該回撥中做一些事情。)
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
// 1. 清理資源快取
// 2. 如果存在初始化生命週期處理器,則建立lifecycleProcessor bean,否則建立預設的DefaultLifecycleProcessor bean
// 3. 委託給LifecycleProcessor去呼叫所有實現了SmartLifecycle bean的start方法 (這裡SmartLifecycle的使用場景主要是在Spring載入和初始化所有bean後,接著執行一些任務或者啟動需要的非同步服務)
// 4. 釋出最後的訊息
// 5. 將環境註冊到LiveBeansView:如果存在spring.liveBeansView.mbeanDomain配置則註冊LiveBeansView到MBeanServer中(其實現了LiveBeansViewMBean介面的getSnapshotAsJson,主要用於將環境轉換為json)
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.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core,since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
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CreateBean -- 建立Bean例項解析
// 先說一下createBean
// 經過resolveBeforeInstantiation方法後,如果建立了代理(即重寫了InstantiationAwareBeanPostProcessor的postProcessBeforeInstantiation方法並且在方法中改變了bean)直接返回即可,否則進行常規bean的建立
@Override
AbstractAutowireCapableBeanFactory.createBean(String beanName,RootBeanDefinition mbd,@Nullable Object[] args){
}
// 常規執行建立bean的邏輯
// 這裡BeanWrapper相當於一個代理器,Spring委託BeanWrapper完成Bean屬性的填充工作。在Bean例項被InstantiatioonStrategy創建出來之後,容器主控程式將Bean例項通過BeanWrapper包裝起來
protected Object doCreateBean(final String beanName,final RootBeanDefinition mbd,final Object[] args){
//Instantiate the bean
BeanWrapper instanceWrapper = null;
if(mbd.isSingleton()){
// 清理快取中的bean
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if(instanceWrapper == null){
// 使用對應的策略建立新的例項:工廠方法,建構函式自動注入,簡單初始化
instanceWrapper = createBeanInstance(beanName,mbd,args);
}
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 {
// MergedBeanDefinitionPostProcessor介面是在合併處理Bean定義的時候的回撥
// 這兒方法是將MergedBeanDefinitionPostProcessor應用到這個特定的bean定義上
applyMergedBeanDefinitionPostProcessors(mbd,beanType,beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(),beanName,"Post-processing of merged bean definition failed",ex);
}
mbd.postProcessed = true;
}
}
//是否需要提前曝光:單例&允許迴圈依賴&bean正在建立
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences && isSingletonCurrentlyInCreation(beanName));
if(earlySingletonExposure){
addSingletonFactory(beanName,new ObjectFactory(){public Object getObject() throws BeansException{
//對bean再一次依賴引用,主要引用SmartInstantiationAwareBeanPostProcessor,
//AOP就是在這裡將advice動態織入bean中,若沒有直接返回bean.
return getEarlyBeanReference(beanName,bean);
}});
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
//對bean進行填充,將各個屬性值注入,可能存在依賴於其他bean的屬性,遞迴依賴bean
populateBean(beanName,instanceWrapper);
//呼叫初始化方法 如 init-method
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(),"Initialization of bean failed",ex);
}
}
if(earlySingletonExposure){
Object earlySingletonReference = getSingleton(beanName,false);
// 如果有迴圈依賴
if(earlySingletonReference != null){
//沒有被代理增強
if(exposedObject == bean){
exposedObject = earlySingletonReference;
}else if(!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)){
String[] dependentBeans = getDependentBeans(beanName);
Set<String> actualDependentBeans = new LinkedHashSet<String>(dependentBeans.length);
for(String dependentBean : dependentBeans){
//檢測依賴
if(!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)){
actualDependentBeans.add(dependentBean);
}
}
//如果actualDependentBeans不為空表示當前bean建立後其依賴的bean卻沒有建立完,說明存在迴圈依賴
if (!actualDependentBeans.isEmpty()) {
throw new BeanCurrentlyInCreationException(beanName,"Bean with name '" + beanName + "' has been injected into other beans [" +
StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
"] in its raw version as part of a circular reference,but has eventually been " +
"wrapped. This means that said other beans do not use the final version of the " +
"bean. This is often the result of over-eager type matching - consider using " +
"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off,for example.");
}
}
}
try{
//註冊為一次性可銷燬的bean
registerDisposableBeanIfNecessary(beanName,bean,mbd);
}catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(),"Invalid destruction signature",ex);
}
return exposedObject;
}
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GetBean -- 解析Bean的初始化
// 重點解析Bean的初始化 -- getBean(name) 為例
@Override
public Object getBean(String name) throws BeansException {
return doGetBean(name,null,false);
}
// 四個引數:第一個為傳入的beanName,第二個為bean的Class型別,第三個表示建立bean需要的引數,最後一個表示不需要進行型別檢查。
protected <T> T doGetBean(final String name,@Nullable final Class<T> requiredType,@Nullable final Object[] args,boolean typeCheckOnly) throws BeansException {
// 將是factoryBean的名稱去掉 之前加的 “&” 符號
final String beanName = transformedBeanName(name);
Object bean;
// 1. 檢測是不是Spring手動註冊的那些單例bean
// 2. 如果是,那麼再檢測是不是工廠bean,如果是返回其工廠方法返回的例項,如果不是返回bean本身。
// Eagerly check singleton cache for manually registered singletons.
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
if (logger.isTraceEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +
"' that is not fully initialized yet - a consequence of a circular reference");
}
else {
logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
}
}
bean = getObjectForBeanInstance(sharedInstance,name,null);
}
else {
// Fail if we're already creating this bean instance:
// We're assumably within a circular reference.
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// 如果父容器存在,並且存在此bean定義,那麼交由其父容器初始化bean
// Check if bean definition exists in this factory.
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
// 將是factoryBean的name前加上 “&” ,因為在父容器中又會再次進行這個轉換操作,所以這裡還需要加上 &
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {
return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
nameToLookup,requiredType,args,typeCheckOnly);
}
// 下面都是交給父容器去載入
else if (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup,args);
}
else if (requiredType != null) {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup,requiredType);
}
else {
return (T) parentBeanFactory.getBean(nameToLookup);
}
}
// 這裡使用了synchronized的雙重校驗來將這個beanName加入到alreadyCreated中,用以防止有其他程式在同一時間建立
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
try {
// 獲取到具有父子關係的bean定義的根節點
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd,args);
// 拿到這個bean所依賴的所有bean定義根節點,並遞迴呼叫初始化它們
// Guarantee initialization of beans that the current bean depends on.
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dep : dependsOn) {
// registerDependentBean進行了依賴關係的註冊,這麼做的原因是Spring在即進行bean銷燬的時候會首先銷燬被依賴的bean。依賴關係的儲存是通過一個ConcurrentHashMap<String,Set>完成的,key是bean名字。
if (isDependent(beanName,dep)) {
throw new BeanCreationException(mbd.getResourceDescription(),"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
registerDependentBean(dep,beanName);
try {
// getBean方法是包括了所有scope的初始化的
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(),"'" + beanName + "' depends on missing bean '" + dep + "'",ex);
}
}
}
// Create bean instance.
if (mbd.isSingleton()) {
//
// 1. getSingleton首先會嘗試去獲取這個Bean
// 2. 然後判斷是否為空,是否正在建立中,如果是則跳過,直接返回獲取到的Bean
// 3. 如果都沒有,則嘗試createBean去建立Bean
// 4. 然後就是一些收尾工作,把Bean加到singletonObjects中
sharedInstance = getSingleton(beanName,() -> {
try {
return createBean(beanName,args);
}
catch (BeansException ex) {
// Explicitly remove instance from singleton cache: It might have been put there
// eagerly by the creation process,to allow for circular reference resolution.
// Also remove any beans that received a temporary reference to the bean.
destroySingleton(beanName);
throw ex;
}
});
bean = getObjectForBeanInstance(sharedInstance,mbd);
}
else if (mbd.isPrototype()) {
// It's a prototype -> create a new instance.
Object prototypeInstance = null;
try {
// 確保在同一時刻只有一個Bean在初始化
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName,args);
}
finally {
// 標記此bean已經沒有處於例項化時段了
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance,mbd);
}
// 其餘諸如:request、session這樣的Scope的初始化,這裡就和前面的單例初始化比較雷同,不講了
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,args);
}
finally {
afterPrototypeCreation(beanName);
}
});
bean = getObjectForBeanInstance(scopedInstance,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;
}
}
// Check if required type matches the type of the actual bean instance.
if (requiredType != null && !requiredType.isInstance(bean)) {
try {
T convertedBean = getTypeConverter().convertIfNecessary(bean,requiredType);
if (convertedBean == null) {
throw new BeanNotOfRequiredTypeException(name,bean.getClass());
}
return convertedBean;
}
catch (TypeMismatchException ex) {
if (logger.isTraceEnabled()) {
logger.trace("Failed to convert bean '" + name + "' to required type '" +
ClassUtils.getQualifiedName(requiredType) + "'",ex);
}
throw new BeanNotOfRequiredTypeException(name,bean.getClass());
}
}
return (T) bean;
}
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