Spring5.0源碼深度解析之SpringBean的生命週期

時間 2019-11-13

標籤 spring5.0 spring 源碼深度解析 springbean 生命週期欄目 Spring 简体版

原文原文鏈接

SpringBean的生命週期

一：單例與多例對象是如何初始化

單例默認狀況下是在容器被加載的時候就會初始化spring

多例是在每次獲取Bean對象的時候初始化設計模式

代碼驗證：緩存

@Component
public class UserEntity {
    public UserEntity() {
        System.out.println(">>>>UserEntity無參數構造函數執行...");
    }

@Configuration
@ComponentScan("com.mayikt.entity")
public class MyConfig {
}

>>>>UserEntity無參數構造函數執行...app

當加上@Scope("prototype")，沒有輸出結果ide

@Component
@Scope("prototype")
public class UserEntity {
    public UserEntity() {
        System.out.println(">>>>UserEntity無參數構造函數執行...");
    }

說明單例默認是在容器被加載的時候初始化，多例是在每次獲取Bean對象的時候初始化。函數

二：Bean對象的初始化與銷燬過程01

Bean初始化：指的就是對象已經建立，裏面的全部set方法都已經執行完畢了。源碼分析

舉個例子：post

@Configuration
@ComponentScan("com.mayikt.entity")
public class MyConfig {

    /**
     * initMethod：指定初始化方法執行
     * destroyMethod：指定銷燬方法
     * @return
     */
    @Bean(initMethod = "initMethod",destroyMethod = "destroyMethod")
    public UserEntity userEntity(){
        return new UserEntity();
    }
}

@Component
public class UserEntity {
    public UserEntity() {
        System.out.println(">>>>UserEntity無參數構造函數執行...");
    }
    /**
     * 思考：initMethod是在無參構造函數以前執行仍是後執行..
     */
    private void initMethod() {
        System.out.println(">>>>UserEntity initMethod 執行...");
    }
    private void destroyMethod() {
        System.out.println(">>>>UserEntity destroyMethod 執行...");
    }
}

public static void main(String[] args) {
    /**
     * IOC容器初始化單例對象都是循環遍歷調用getBean方法
     */
    AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MyConfig.class);
    applicationContext.close();

返回結果ui

>>>>UserEntity無參數構造函數執行...
>>>>UserEntity initMethod 執行...
>>>>UserEntity destroyMethod 執行...this

構造函數：Bean的建立，Map集合存儲對象

initMethod：表示對象已經建立成功以後執行

destroyMethod：表示對象被銷燬以後執行，clean

destroyMethod方法執行時，至關於調用了close方法去銷燬Bean

applicationContext.close();

public void close() {
   synchronized (this.startupShutdownMonitor) {
      doClose();
      // If we registered a JVM shutdown hook, we don't need it anymore now:
      // We've already explicitly closed the context.
      if (this.shutdownHook != null) {
         try {
            Runtime.getRuntime().removeShutdownHook(this.shutdownHook);
         }
         catch (IllegalStateException ex) {
            // ignore - VM is already shutting down
         }
      }
   }
}

protected void doClose() {
   if (this.active.get() && this.closed.compareAndSet(false, true)) {
     ....
      // Destroy all cached singletons in the context's BeanFactory.
      destroyBeans();

      // Close the state of this context itself.
      closeBeanFactory();

      // Let subclasses do some final clean-up if they wish...
      onClose();

      this.active.set(false);
   }
}

protected void destroyBeans() {
   getBeanFactory().destroySingletons();
}

public void destroySingletons() {
    super.destroySingletons();
    this.manualSingletonNames.clear();
    this.clearByTypeCache();
}

private void clearByTypeCache() {
    this.allBeanNamesByType.clear();
    this.singletonBeanNamesByType.clear();
}

上面執行了clear操做，再回到前面

這裏給用戶自定義關閉操做：模板方法設計模式

protected void onClose() {
   // For subclasses: do nothing by default.
}

再把活躍狀態設置爲false。

三：Bean對象的初始化與銷燬過程02

1.實現InitializingBean,DisposableBean兩個接口

@Component
public class MemberEntity implements InitializingBean,DisposableBean{
    //     implements InitializingBean, DisposableBean
    public MemberEntity() {
        System.out.println("無參構造函數執行..");
    }
    // afterPropertiesSet initMet hod
    // 1.對象建立 對象屬性賦值 set方法所有走完
    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("MemberEntity >>>afterPropertiesSet");
    }
    @Override
    public void destroy() throws Exception {
        System.out.println("MemberEntity >>> destroy");
    }
}

輸出結果：

無參構造函數執行..
MemberEntity >>>afterPropertiesSet
MemberEntity >>> destroy

2.使用Java封裝的註解方式@PostConstruct， @PreDestroy

@Component
public class MemberEntity{
    //     implements InitializingBean, DisposableBean
    public MemberEntity() {
        System.out.println("無參構造函數執行..");
    }
    // afterPropertiesSet initMet hod
    // 1.對象建立 對象屬性賦值 set方法所有走完
   @PostConstruct
    public void afterPropertiesSet() throws Exception {
        System.out.println("MemberEntity >>>afterPropertiesSet");
    }
    @PreDestroy
    public void destroy() throws Exception {
        System.out.println("MemberEntity >>> destroy");
    }
}

輸出結果

無參構造函數執行..
MemberEntity >>>afterPropertiesSet
MemberEntity >>> destroy

四：如今咱們開始分析SpringBean的生命週期

SpringBean生命週期有個很好的理念就是後置處理器BeanPostProcessor

後置處理器：BeanPostProcessor

BeanPostProcessor引入：

@Component
public class MyApplicationContext implements ApplicationContextAware {
    private ApplicationContext applicationContext;
    /**
     * spring底層中爲何可以實現ApplicationContextAware接口 就可以拿到ApplicationContext
     * @param applicationContext
     * @throws BeansException
     */
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        MemberEntity memberEntity = applicationContext.getBean("memberEntity", MemberEntity.class);
        System.out.println("memberEntity：" + memberEntity);
    }
}

@Configuration
@ComponentScan("com.mayikt.entity")
@Import(MyApplicationContext.class)//這裏注入到spring容器中
public class MyConfig {}

輸出結果：對象初始化，賦值完畢，就能夠經過setApplicationContext拿到bean對象

memberEntity：com.mayikt.entity.MemberEntity@11e21d0e

思考問題：spring底層中爲何可以實現ApplicationContextAware接口就可以拿到ApplicationContext

關鍵就是在於：BeanPostProcessor

下面咱們開始分析：BeanPostProcessor後置處理器（很是重要！！！）

AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MyConfig.class);

public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) {
   this();
   register(annotatedClasses);
   refresh();
}

public void refresh() throws BeansException, IllegalStateException {
   synchronized (this.startupShutdownMonitor) {
    ....
      try {
      ....
         // Instantiate all remaining (non-lazy-init) singletons.
         finishBeanFactoryInitialization(beanFactory);
      }
....
}

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
 ....
   // Instantiate all remaining (non-lazy-init) singletons.
   beanFactory.preInstantiateSingletons();
}

@Override
public void preInstantiateSingletons() throws BeansException {
    ....
   List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

   for (String beanName : beanNames) {
      RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
      if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
         if (isFactoryBean(beanName)) {
            final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
            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 {
            getBean(beanName);
         }
      }
   }
....
}

@Override
public Object getBean(String name) throws BeansException {
   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 {
....
   Object sharedInstance = getSingleton(beanName);//檢測緩存中或者實例工廠中是否有對應的實例
   if (sharedInstance != null && args == null) {
      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 + "'");
         }
      }
      bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);//返回對應的實例，有時候存在諸如BeanFactory的狀況並非直接返回實例自己而是返回指定方法返回的實例
   }

   else {
      // Fail if we're already creating this bean instance:
      // We're assumably within a circular reference.
      if (isPrototypeCurrentlyInCreation(beanName)) {//只有在單例狀況下才會去嘗試解決循環依賴
         throw new BeanCurrentlyInCreationException(beanName);
      }

      // Check if bean definition exists in this factory.
      BeanFactory parentBeanFactory = getParentBeanFactory();
      if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {//若是beaanDefinitionMap中也就是在全部已經加載的類中不包括beanName則嘗試從parentBeanFactory中檢測
         // Not found -> check parent.
         String nameToLookup = originalBeanName(name);
         if (parentBeanFactory instanceof AbstractBeanFactory) {
            return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
                  nameToLookup, requiredType, args, typeCheckOnly);
         }
         else if (args != null) {//遞歸到BeanFactory中尋找
            // 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) {//若是不是僅僅作類型檢查，則是建立Bean，這裏進行記錄
         markBeanAsCreated(beanName);
      }

      try {
         final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);//轉換爲RootBeanDefinition
         checkMergedBeanDefinition(mbd, beanName, args);

         // Guarantee initialization of beans that the current bean depends on.
         String[] dependsOn = mbd.getDependsOn();
         if (dependsOn != null) {//若存在依賴則須要遞歸實例化依賴的Bean
            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);//緩存依賴調用
               getBean(dep);
            }
         }

         // Create bean instance.
         if (mbd.isSingleton()) {//實例化依賴的bean後，即可實例化mbd自己了，單例模式的建立
            sharedInstance = getSingleton(beanName, () -> {
               try {
                  return createBean(beanName, mbd, args);
               }
               catch (BeansException ex) {
                  destroySingleton(beanName);
                  throw ex;
               }
            });
            bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
         }

         else if (mbd.isPrototype()) {//prototype模式的建立
            // 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;
      }
   }

   // Check if required type matches the type of the actual bean instance.
   if (requiredType != null && !requiredType.isInstance(bean)) {//檢測須要的類型是否符合實際bean的類型
      try {
         T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
         if (convertedBean == null) {
            throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
         }
         return convertedBean;
      }
      catch (TypeMismatchException ex) {
         if (logger.isDebugEnabled()) {
            logger.debug("Failed to convert bean '" + name + "' to required type '" +
                  ClassUtils.getQualifiedName(requiredType) + "'", ex);
         }
         throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
      }
   }
   return (T) bean;
}

步驟大體以下：

1.轉換BeanName

2.嘗試從緩存中加載單例bean

3.Bean的實例化

4.原型模式的依賴檢查

5.檢查parentBeanFactory

6.將存儲XML配置文件的GernericBeanDefinition轉換爲RootBeanDefinition

7.尋找依賴

8.針對不一樣的scope進行bean的建立

9.類型轉換

判斷是單例：

if (mbd.isSingleton()) {
   sharedInstance = getSingleton(beanName, () -> {
      try {
         return createBean(beanName, mbd, args);
      }
      catch (BeansException ex) {
         destroySingleton(beanName);
         throw ex;
      }
   });
   bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}

@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
      throws BeanCreationException {
....
      Object beanInstance = doCreateBean(beanName, mbdToUse, args);
   ....
}

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
      throws BeanCreationException {

   final Object bean = instanceWrapper.getWrappedInstance();
....
   Object exposedObject = bean;
   try {
      populateBean(beanName, mbd, instanceWrapper);//循環給屬性賦值
      exposedObject = initializeBean(beanName, exposedObject, mbd);
   }
....
}

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
    if (System.getSecurityManager() != null) {
        AccessController.doPrivileged(() -> {
            this.invokeAwareMethods(beanName, bean);
            return null;
        }, this.getAccessControlContext());
    } else {
        this.invokeAwareMethods(beanName, bean);
    }

    Object wrappedBean = bean;
    if (mbd == null || !mbd.isSynthetic()) {
        wrappedBean = this.applyBeanPostProcessorsBeforeInitialization(bean, beanName);
    }

    try {
        this.invokeInitMethods(beanName, wrappedBean, mbd);//執行自定義的init方法
    } catch (Throwable var6) {
        throw new BeanCreationException(mbd != null ? mbd.getResourceDescription() : null, beanName, "Invocation of init method failed", var6);
    }

    if (mbd == null || !mbd.isSynthetic()) {
        wrappedBean = this.applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
    }

    return wrappedBean;
}

private void invokeAwareMethods(String beanName, Object bean) {
    if (bean instanceof Aware) {
        if (bean instanceof BeanNameAware) {    //判斷類型並設置beanName
            ((BeanNameAware)bean).setBeanName(beanName);
        }

        if (bean instanceof BeanClassLoaderAware) {
            ClassLoader bcl = this.getBeanClassLoader();
            if (bcl != null) {
                ((BeanClassLoaderAware)bean).setBeanClassLoader(bcl);
            }
        }
        if (bean instanceof BeanFactoryAware) {
            ((BeanFactoryAware)bean).setBeanFactory(this);
        }
    }
}

咱們就明白了：IOC容器初始化單例對象都是循環遍歷調用getBean方法。

下面咱們手寫看下springBean的生命週期

@Component
public class PayEntity implements BeanNameAware, BeanFactoryAware, InitializingBean, ApplicationContextAware {
    public PayEntity() {
        System.out.println("1.對象的實例化完成..");
    }

    @Override
    public void setBeanName(String name) {
        System.out.println("2.對象beanName:" + name);
    }
    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        System.out.println("3.beanFactory:" + beanFactory);
    }
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        System.out.println("4.獲取到applicationContext對象");
    }
    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("5.bean init方法執行..");
    }

輸出結果

1.對象的實例化完成..
2.對象beanName:payEntity
3.beanFactory:org.springframework.beans.factory.support.DefaultListableBeanFactory@55f3ddb1: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.event.internalEventListenerProcessor,org.springframework.context.event.internalEventListenerFactory,myConfig,payEntity]; root of factory hierarchy
4.獲取到applicationContext對象
5.bean init方法執行..

BeanPostProcessor的做用

protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
 ....
   if (mbd == null || !mbd.isSynthetic()) {
      wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);//init以前處理操做
   }
....
   try {
      invokeInitMethods(beanName, wrappedBean, mbd);//init執行邏輯
   }
 ....
   if (mbd == null || !mbd.isSynthetic()) {
      wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);//init以後處理操做
   }

   return wrappedBean;
}

BeanPostProcessor後置處理器的前置處理邏輯和後置處理邏輯:

public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
      throws BeansException {
   for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
      Object current = beanProcessor.postProcessBeforeInitialization(result, beanName);
   ...
}

public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
      throws BeansException {
   for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
      Object current = beanProcessor.postProcessAfterInitialization(result, beanName);
     ...
}

咱們自定義類實現BeanPostProcessor

@Component
public class MyBeanPostProcessor implements BeanPostProcessor {
    //BeanPostProcessor 後置處理器 對咱們bean的對象實現加強
    @Override
    // 執行自定義init方法以前處理
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("執行init方法以前處理 : " + beanName);
        return bean;
    }

    @Override
    // 執行自定義init方法以後處理
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("執行init方法以後處理 :" + beanName);
        return bean;
    }
    //BeanPostProcessor  後置處理
    // Aware    實現
}

輸出結果：

執行init方法以前處理 : org.springframework.context.event.internalEventListenerProcessor
執行init方法以後處理 :org.springframework.context.event.internalEventListenerProcessor
執行init方法以前處理 : org.springframework.context.event.internalEventListenerFactory
執行init方法以後處理 :org.springframework.context.event.internalEventListenerFactory
執行init方法以前處理 : myConfig
執行init方法以後處理 :myConfig
1.對象的實例化完成..
2.對象beanName:payEntity
3.beanFactory:org.springframework.beans.factory.support.DefaultListableBeanFactory@55f3ddb1: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.event.internalEventListenerProcessor,org.springframework.context.event.internalEventListenerFactory,myConfig,payEntity,com.mayikt.processor.MyBeanPostProcessor]; root of factory hierarchy
4.獲取到applicationContext對象
執行init方法以前處理 : payEntity
5.bean init方法執行..
執行init方法以後處理 :payEntity

ApplicationAware接口原理

實現ApplicationAware接口怎麼就能夠setApplicationContext呢？

@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
    System.out.println("4.獲取到applicationContext對象");
}

public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
      throws BeansException {

   Object result = existingBean;
   for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
      Object current = beanProcessor.postProcessAfterInitialization(result, beanName);
      if (current == null) {
         return result;
      }
      result = current;
   }
   return result;
}

@Override
public Object postProcessAfterInitialization(Object bean, String beanName) {
   return bean;
}

發現BeanPostProcessor後置處理器的postProcessAfterInitialization後置處理什麼也沒作:

再去前置找：

public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
      throws BeansException {

   Object result = existingBean;
   for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
      Object current = beanProcessor.postProcessBeforeInitialization(result, beanName);
      if (current == null) {
         return result;
      }
      result = current;
   }
   return result;
}

public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {
   AccessControlContext acc = null;

   if (System.getSecurityManager() != null &&
         (bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
               bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
               bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) {
      acc = this.applicationContext.getBeanFactory().getAccessControlContext();
   }

   if (acc != null) {
      AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
         invokeAwareInterfaces(bean);
         return null;
      }, acc);
   }
   else {
      invokeAwareInterfaces(bean);
   }

   return bean;
}

private void invokeAwareInterfaces(Object bean) {
   if (bean instanceof Aware) {
      if (bean instanceof EnvironmentAware) {
         ((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
      }
      if (bean instanceof EmbeddedValueResolverAware) {
         ((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
      }
      if (bean instanceof ResourceLoaderAware) {
         ((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
      }
      if (bean instanceof ApplicationEventPublisherAware) {
         ((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
      }
      if (bean instanceof MessageSourceAware) {
         ((MessageSourceAware) bean).setMessageSource(this.applicationContext);
      }
      if (bean instanceof ApplicationContextAware) {//判斷ApplicationContextAware類型，賦值
         ((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
      }
   }
}

看到沒有，最後判斷：bean instanceof ApplicationContextAware類型，再賦值

咱們就能夠知道上面提出的這個問題：實現ApplicationAware接口怎麼就能夠setApplicationContext？

因此咱們知道ApplicationContextAware是經過BeanPostProcessor後置處理器的postProcessBeforeInitialization前置處理實現的。

SpringBean的生命週期總結

源碼分析流程：

1.進入到刷新refresh（）方法

2.finishBeanFactoryInitialization（）初始化全部單例對象

3.preInstantiateSingletons（）初始化全部的單例對象：注意是非懶加載

4.getBean（）-》doGetBean（）先查詢該對象是否有初始化過，沒有的化就建立註冊到IOC容器中

5.createBean（）判斷對象若是是單例的狀況下，就調用該方法去建立對象

6.doCreateBean（）建立IOC對象

7.createBeanInstance（）使用Java的反射機制實例化咱們的對象

8.populateBean（）給對象的set屬性賦值

9.initializeBean（）執行初始化方法（也能夠本身定義初始化的方法）

10.invokeAwareMethods（）判斷bean的類型是不是Aware相關依賴，若是存在的狀況回調方法

11.applyBeanPostProcessorsBeforeInitialization（）在初始化方法以前執行處理（加強）

12.invokeInitMethods（）調用自定義的init方法，Java反射技術

13.applyBeanPostProcessorsAfterInitialization（）在初始化方法以後執行處理（加強）

14.正常是用咱們初始化好的這個Bean對象

15.銷燬bean