spring原始碼學習(二)
本篇文章,來介紹finishBeanFactoryInitialization(beanFactory);這個方法主要是完成bean的例項化,
invokeBeanFactoryPostProcessors(beanFactory);負責把所有的bean掃描到beanDefinitionMap中;
下面來說是如何初始化的
org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean
我們直接從這個方法開始說起,前面的呼叫鏈簡單,就不說了
1 protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType, 2 @Nullable final Object[] args, boolean typeCheckOnly) throws BeansException { 3 4 /** 5 * 通過name獲取beanName,這裡不使用name直接作為beanName有兩個原因: 6 * 1.name可能是以&開頭的,表明呼叫者想獲取FactoryBean本身,而非FactoryBean;在beanFactory中factoryBean的儲存也是map格式 7 * <beanName,bean> 只是說,普通的beanName是沒有&這個字串的,所以,需要將name的首字母移除,這樣才能從快取中拿到factoryBean 8 * 2.還是別名的問題,需要轉換 9 */ 10 final String beanName = transformedBeanName(name); 11 Object bean; 12 13 /** 14 * 1.從單例池中獲取當前bean 15 * 2.這裡是迴圈依賴的重要方法之一 16 * 17 */ 18 // Eagerly check singleton cache for manually registered singletons. 19 Object sharedInstance = getSingleton(beanName); 20 if (sharedInstance != null && args == null) { 21 if (logger.isDebugEnabled()) { 22 if (isSingletonCurrentlyInCreation(beanName)) { 23 logger.debug("Returning eagerly cached instance of singleton bean '" + beanName + 24 "' that is not fully initialized yet - a consequence of a circular reference"); 25 } 26 else { 27 logger.debug("Returning cached instance of singleton bean '" + beanName + "'"); 28 } 29 } 30 bean = getObjectForBeanInstance(sharedInstance, name, beanName, null); 31 } 32 33 else { 34 // Fail if we're already creating this bean instance: 35 // We're assumably within a circular reference. 36 /** 37 * 這裡判斷bean是否在建立過程中,是第二次呼叫的時候 才會判斷;如果是第一次執行到這裡,set集合是空(這裡判斷的是原型bean) 38 */ 39 if (isPrototypeCurrentlyInCreation(beanName)) { 40 throw new BeanCurrentlyInCreationException(beanName); 41 } 42 43 //新增到alreadyCreated集合當中,表示當前bean已經建立過一次了 44 if (!typeCheckOnly) { 45 markBeanAsCreated(beanName); 46 } 47 48 try { 49 final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName); 50 checkMergedBeanDefinition(mbd, beanName, args); 51 52 // Guarantee initialization of beans that the current bean depends on. 53 String[] dependsOn = mbd.getDependsOn(); 54 if (dependsOn != null) { 55 for (String dep : dependsOn) { 56 if (isDependent(beanName, dep)) { 57 throw new BeanCreationException(mbd.getResourceDescription(), beanName, 58 "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'"); 59 } 60 registerDependentBean(dep, beanName); 61 try { 62 getBean(dep); 63 } 64 catch (NoSuchBeanDefinitionException ex) { 65 throw new BeanCreationException(mbd.getResourceDescription(), beanName, 66 "'" + beanName + "' depends on missing bean '" + dep + "'", ex); 67 } 68 } 69 } 70 71 // Create bean instance.如果當前bean是單例項的,就呼叫createBean 72 if (mbd.isSingleton()) { 73 sharedInstance = getSingleton(beanName, () -> { 74 try { 75 return createBean(beanName, mbd, args); 76 } 77 catch (BeansException ex) { 78 // Explicitly remove instance from singleton cache: It might have been put there 79 // eagerly by the creation process, to allow for circular reference resolution. 80 // Also remove any beans that received a temporary reference to the bean. 81 destroySingleton(beanName); 82 throw ex; 83 } 84 }); 85 bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd); 86 } 87 } 88 catch (BeansException ex) { 89 cleanupAfterBeanCreationFailure(beanName); 90 throw ex; 91 } 92 } 93 94 95 return (T) bean; 96 }
粘貼出來的方法刪減了一部分程式碼,我們只說單例項bean的初始化;
在判斷當前bean是單例項的時候,會呼叫createBean;在getSingleton這裡,有一行程式碼,是把當前bean新增到一個set集合中(這個set集合表示當前bean正在建立過程中),
這個set是用來解決迴圈依賴問題的,在後面,會單獨抽出一篇來介紹迴圈引用是如何解決的,在這裡就先跳過;
在createBean的方法中,會呼叫createBeanInstance(beanName, mbd, args); 這個方法主要是完成bean的初始化,在方法中會呼叫org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor#determineCandidateConstructors;
這個後置處理器的determineCandidateConstructors方法來推斷使用哪個建構函式來初始化;
這個方法裡面,我目前也正在學習,後續會貼出對這個方法的學習筆記,這裡先暫時跳過;(我們就認為createBeanInstance方法完成了bean的建立),
推斷出使用哪個建構函式之後,會初始化bean,返回的是一個BeanWrapper物件。這裡創建出來的僅僅是bean物件;需要經過後面的屬性注入,以及初始化,才會變成我們所說的spring bean物件;
1 protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args) 2 throws BeanCreationException { 3 4 // Instantiate the bean. 5 BeanWrapper instanceWrapper = null; 6 if (mbd.isSingleton()) { 7 instanceWrapper = this.factoryBeanInstanceCache.remove(beanName); 8 } 9 if (instanceWrapper == null) { 10 /** 11 * 建立bean例項,並將bean例項包裹在BeanWrapper實現類物件中返回, 12 * createBeanInstance中包含三種建立bean的方式 13 * 1.通過工廠方法建立bean例項 14 * 2.通過構造方法自動注入的方式建立bean例項 15 * 3.通過無參構造方法建立bean例項 16 * 17 * 如果bean的配置中配置了lookup-method和replace-method 則會使用增強bean例項 18 * 19 * 在這個方法中完成了對bean的建立(僅僅是new出來,也就是說在這個方法裡面推斷要使用哪個建構函式來建立bean物件) 20 * 然後完成bean的初始化 21 * 22 */ 23 instanceWrapper = createBeanInstance(beanName, mbd, args); 24 } 25 final Object bean = instanceWrapper.getWrappedInstance(); 26 Class<?> beanType = instanceWrapper.getWrappedClass(); 27 if (beanType != NullBean.class) { 28 mbd.resolvedTargetType = beanType; 29 } 30 31 // Allow post-processors to modify the merged bean definition. 32 synchronized (mbd.postProcessingLock) { 33 if (!mbd.postProcessed) { 34 try { 35 //mpy 第三次呼叫後置處理器 快取註解資訊 36 applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName); 37 } 38 catch (Throwable ex) { 39 throw new BeanCreationException(mbd.getResourceDescription(), beanName, 40 "Post-processing of merged bean definition failed", ex); 41 } 42 mbd.postProcessed = true; 43 } 44 } 45 46 // Eagerly cache singletons to be able to resolve circular references 47 // even when triggered by lifecycle interfaces like BeanFactoryAware. 48 boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences && 49 isSingletonCurrentlyInCreation(beanName)); 50 if (earlySingletonExposure) { 51 if (logger.isDebugEnabled()) { 52 logger.debug("Eagerly caching bean '" + beanName + 53 "' to allow for resolving potential circular references"); 54 } 55 //mpy 第四次呼叫後置處理器 獲取一個提前暴露的物件 用來解決迴圈依賴 56 addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean)); 57 } 58 59 // Initialize the bean instance. 60 Object exposedObject = bean; 61 try { 62 //在populateBean(beanName, mbd, instanceWrapper);方法中完成第五次第六次呼叫後置處理器 63 populateBean(beanName, mbd, instanceWrapper); 64 //在initialzeBean中完成第七次第八次後置處理器呼叫 65 exposedObject = initializeBean(beanName, exposedObject, mbd); 66 } 67 catch (Throwable ex) { 68 if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) { 69 throw (BeanCreationException) ex; 70 } 71 else { 72 throw new BeanCreationException( 73 mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex); 74 } 75 } 76 return exposedObject; 77 }
上面這個方法中,呼叫第四次後置處理器這裡,返回了一個object物件,這個方法是為了完成迴圈依賴的,放到後面一起講,
在populateBean中,會完成屬性的注入,比如@AutoWired,@Value這個屬性值注入
initializeBean方法,主要是呼叫bean的初始化方法
bean的初始化有三種方式:
1.@Bean註解中指定 initMethod destroyMethod
2.@PostConstruct @PreDestroy
3.實現DisposableBean和InitializingBean介面
在方法執行完之後,會把建立好的bean物件存放到singletonObjects這個map中,這個map存放的是所有例項化好的物件;如果bean是原型的,在第二次getBean的時候,會從這個map中獲取到bean物件
從狹義上來講,singletonObjects就是我們所說的spring容器
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