// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);

@Component
public class MyService {
  @Autowired
  private Dao dao;

  public void query(){
    System.out.println("executing query method");
    dao.query();
  }
}

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
  //如果bdMap中存在conversionService，則進(jìn)行初始化
  //該bean可用來提供數(shù)據(jù)的轉(zhuǎn)化功能
  if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
      beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
    beanFactory.setConversionService(
        beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
  }
  if (!beanFactory.hasEmbeddedValueResolver()) {
    beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
  }
  //初始化類型為LoadTimeWeaverAware的bean
  //可用于AspectJ靜態(tài)織入過程
  String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
  for (String weaverAwareName : weaverAwareNames) {
    getBean(weaverAwareName);
  }
  //銷毀之前在prepareBeanFactory()中生成的臨時(shí)ClassLoader
  beanFactory.setTempClassLoader(null);
  //在這凍結(jié)對BeanDefinition的修改
  //防止spring在初始化的時(shí)候發(fā)生BeanDefinition的修改
  beanFactory.freezeConfiguration();
  beanFactory.preInstantiateSingletons();
}

public void preInstantiateSingletons() throws BeansException {
  if (logger.isDebugEnabled()) {
    logger.debug("Pre-instantiating singletons in " + this);
  }
  //得到所有bean的名字
  List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
  for (String beanName : beanNames) {
    //做了合并父類的BeanDefinition的操作
    //在會(huì)用xml配置bean時(shí) 有一個(gè)parent 屬性，可以繼承類名，作用域等 
    RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
    if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
      //判斷是FactoryBean
      if (isFactoryBean(beanName)) {
        //如果是FactoryBean則加上 &
        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 { //不是factoryBean的情況
        getBean(beanName);
      }
    }
  }
  ...

public interface FactoryBean<T> {
  T getObject() throws Exception;
  Class<?> getObjectType();
  default boolean isSingleton() {
    return true;
  }
}

@Component
public class MyFactoryBean implements FactoryBean {
    @Override
    public Object getObject() throws Exception {
        return new TestDao();
    }
    @Override
    public Class<?> getObjectType() {
        return TestDao.class;
    }
}

System.out.println(context.getBean("myFactoryBean"));
System.out.println(context.getBean("&myFactoryBean"));

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 {
  final String beanName = transformedBeanName(name);
  Object bean;
  //先嘗試從spring容器中獲取一次，如果為空則實(shí)例化
  Object sharedInstance = getSingleton(beanName);
  //在調(diào)用getBean時(shí)，args為空
  //如果不為空，那么意味著調(diào)用方不是希望獲取bean，而是創(chuàng)建bean
  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 + "'");
      }
    }
    /*
    *  如果是普通的單例bean，下面的方法會(huì)直接返回sharedInstance
    *  但如果是FactoryBean 類型的，則需要getObject工廠方法獲得bean實(shí)例
    *  如果想獲取FactoryBean本身，也不會(huì)做特別的處理
    * */
    bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
  }
  else {
    //如果當(dāng)前線程已經(jīng)創(chuàng)建過了prototype類型的這個(gè)bean，拋出異常
    if (isPrototypeCurrentlyInCreation(beanName)) {
      throw new BeanCurrentlyInCreationException(beanName);
    }
    // 如果對spring沒有進(jìn)行改造，這里默認(rèn) parentBeanFactory為空
    BeanFactory parentBeanFactory = getParentBeanFactory();
    if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
      String nameToLookup = originalBeanName(name);
      if (parentBeanFactory instanceof AbstractBeanFactory) {
        return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
            nameToLookup, requiredType, args, typeCheckOnly);
      }
      else if (args != null) {
        return (T) parentBeanFactory.getBean(nameToLookup, args);
      }
      else {
        return parentBeanFactory.getBean(nameToLookup, requiredType);
      }
    }
    if (!typeCheckOnly) {
      //typeCheckOnly為false，添加到alreadyCreated Set集合當(dāng)中，表示它已經(jīng)創(chuàng)建過
      //防止重復(fù)創(chuàng)建
      markBeanAsCreated(beanName);
    }
    //重點(diǎn)部分，創(chuàng)建singleton的bean，或創(chuàng)建新的prototype的bean
    try {
      final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
      checkMergedBeanDefinition(mbd, beanName, args);

      // 判斷當(dāng)前bean是否有依賴，這里指的是使用depends-on的情況，需要先實(shí)例化依賴bean
      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 + "'");
          }
          //注冊依賴關(guān)系
          registerDependentBean(dep, beanName);
          try {
            //初始化被依賴bean
            getBean(dep);
          }
          catch (NoSuchBeanDefinitionException ex) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                "'" + beanName + "' depends on missing bean '" + dep + "'", ex);
          }
        }
      } 
      //在這才真正創(chuàng)建bean的實(shí)例
      if (mbd.isSingleton()) {
        sharedInstance = getSingleton(beanName, () -> {
          try {
            //真正創(chuàng)建功能的語句
            return createBean(beanName, mbd, args);
          }
          catch (BeansException ex) {            
            destroySingleton(beanName);
            throw ex;
          }
        });
        bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
      }
      // 創(chuàng)建 prototype 的實(shí)例
      else if (mbd.isPrototype()) {        
        Object prototypeInstance = null;
        try {
          beforePrototypeCreation(beanName);
          prototypeInstance = createBean(beanName, mbd, args);
        }
        finally {
          afterPrototypeCreation(beanName);
        }
        bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
      }
      //如果不是singleto和prototype,委托給相應(yīng)的實(shí)現(xiàn)類來處理
      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);
        }
      //拋出異常，代碼省略...
  }
  //類型檢查，正常則返回，異常則拋出
  if (requiredType != null && !requiredType.isInstance(bean)) {
    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;
}

Object singletonObject = this.singletonObjects.get(beanName);

private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);

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;
  //確保 BeanDefinition 中的 Class 被加載
  Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
  if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
    mbdToUse = new RootBeanDefinition(mbd);
    mbdToUse.setBeanClass(resolvedClass);
  }
  // 處理 lookup-method 和 replace-method 配置
  // spring中把lookup-method 和 replace-method 統(tǒng)稱為method overrides
  try {
    mbdToUse.prepareMethodOverrides();
  }
  catch (BeanDefinitionValidationException ex) {
    throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
        beanName, "Validation of method overrides failed", ex);
  }
  try {
    //應(yīng)用后置處理器，如果后置處理器返回的bean不為空則直接返回
    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 {//調(diào)用doCreateBean創(chuàng)建bean
    Object beanInstance = doCreateBean(beanName, mbdToUse, args);
    if (logger.isDebugEnabled()) {
      logger.debug("Finished creating instance of bean '" + beanName + "'");
    }
    return beanInstance;
  }
  //非重要代碼省略...
}

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
    throws BeanCreationException {
  //BeanWrapper是一個(gè)包裝接口，真正實(shí)例化的是 BeanWrapperImpl
  BeanWrapper instanceWrapper = null;
  if (mbd.isSingleton()) {
    instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
  }
  if (instanceWrapper == null) {
    //創(chuàng)建bean實(shí)例，并將實(shí)例包裹在 BeanWrapper 實(shí)現(xiàn)類對象中返回
    instanceWrapper = createBeanInstance(beanName, mbd, args);
  }
  // 使用BeanWrapper 產(chǎn)生一個(gè)原生對象
  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 {
        //執(zhí)行后置處理器MergedBeanDefinitionPostProcessor
        applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
      }
      catch (Throwable ex) {
        throw new BeanCreationException(mbd.getResourceDescription(), beanName,
            "Post-processing of merged bean definition failed", ex);
      }
      mbd.postProcessed = true;
    }
  }
  //用于處理循環(huán)依賴，后面單獨(dú)分析
  boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
      isSingletonCurrentlyInCreation(beanName));
  if (earlySingletonExposure) {
    if (logger.isDebugEnabled()) {
      logger.debug("Eagerly caching bean '" + beanName +
          "' to allow for resolving potential circular references");
    }
    //執(zhí)行后置處理器    
    addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
  }
  //到此為止，還是原生對象
  Object exposedObject = bean;
  try {
    //賦值屬性,依賴，非常重要
    populateBean(beanName, mbd, instanceWrapper);
    //執(zhí)行后置處理器,變成代理對象，aop就是在這里完成的處理  
    exposedObject = initializeBean(beanName, exposedObject, mbd);
  }
  //中間非重要代碼省略...
  return exposedObject;
}

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
  //確保加載了該class
  Class<?> beanClass = resolveBeanClass(mbd, beanName);

  //檢測一個(gè)類的訪問權(quán)限 spring默認(rèn)情況下對于public的類是允許訪問的
  if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
    throw new BeanCreationException(mbd.getResourceDescription(), beanName,
        "Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
  }

  Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
  if (instanceSupplier != null) {
    return obtainFromSupplier(instanceSupplier, beanName);
  }

  /*
  *如果工廠方法不為空，則通過工廠方法構(gòu)建bean對象
  * factoryMethod基于xml，實(shí)際工作中很少使用
  *  */
  if (mbd.getFactoryMethodName() != null) {
    return instantiateUsingFactoryMethod(beanName, mbd, args);
  }

  /*
  * 從spring的原始注釋可以知道這個(gè)是一個(gè)ShortCut，當(dāng)多次構(gòu)建同一個(gè)bean時(shí)，可以使用這個(gè)ShortCut
  * 這里的resolved和 mbd.constructorArgumentsResolved 將會(huì)在bean第一次實(shí)例化的過程中被設(shè)置
  * */
  boolean resolved = false;
  boolean autowireNecessary = false;
  if (args == null) {
    synchronized (mbd.constructorArgumentLock) {
      if (mbd.resolvedConstructorOrFactoryMethod != null) {
        resolved = true;
        //如果已經(jīng)解析了構(gòu)造方法的參數(shù)，則必須要通過一個(gè)帶參數(shù)構(gòu)造方法來實(shí)例
        autowireNecessary = mbd.constructorArgumentsResolved;
      }
    }
  }
  if (resolved) {
    if (autowireNecessary) {
      //通過構(gòu)造方法自動(dòng)裝配的方式構(gòu)造bean對象
      return autowireConstructor(beanName, mbd, null, null);
    }
    else {
      //通過默認(rèn)的無參構(gòu)造方法進(jìn)行
      return instantiateBean(beanName, mbd);
    }
  }

  //spring目前不知道用什么方式實(shí)例化這個(gè)bean，所以先拿到所有的構(gòu)造方法
  //由后置處理器決定返回哪些構(gòu)造方法
  Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
  /*
  * AUTOWIRE :  0-NO  ,1-BY_NAME,2-BY_TYPE,3-CONSTRUCTOR
  * 在這里mbd.getResolvedAutowireMode()取到的是0，就是NO
  * */
  if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
      mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
    return autowireConstructor(beanName, mbd, ctors, args);
  }
  //使用默認(rèn)的無參構(gòu)造方法進(jìn)行初始化
  return instantiateBean(beanName, mbd);
}

protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
  try {
    Object beanInstance;
    final BeanFactory parent = this;
    if (System.getSecurityManager() != null) {
      beanInstance = AccessController.doPrivileged((PrivilegedAction<Object>) () ->
          getInstantiationStrategy().instantiate(mbd, beanName, parent),
          getAccessControlContext());
    }
    else {
      // getInstantiationStrategy得到類的實(shí)例化策略
      beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
    }
    BeanWrapper bw = new BeanWrapperImpl(beanInstance);
    initBeanWrapper(bw);
    return bw;
  }
  catch (Throwable ex) {
    throw new BeanCreationException(
        mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
  }
}

public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
  // 檢測bean配置中是否配置了lookup-method 或 replace-method
  //如果配置了就需使用CGLIB構(gòu)建bean對象
  if (!bd.hasMethodOverrides()) {
    Constructor<?> constructorToUse;
    synchronized (bd.constructorArgumentLock) {
      constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod;
      if (constructorToUse == null) {
        final Class<?> clazz = bd.getBeanClass();
        if (clazz.isInterface()) {
          throw new BeanInstantiationException(clazz, "Specified class is an interface");
        }
        try {
          if (System.getSecurityManager() != null) {
            constructorToUse = AccessController.doPrivileged(
                (PrivilegedExceptionAction<Constructor<?>>) clazz::getDeclaredConstructor);
          }
          else {
            //得到默認(rèn)構(gòu)造方法，即使沒有寫也會(huì)有一個(gè)
            constructorToUse = clazz.getDeclaredConstructor();
          }
          bd.resolvedConstructorOrFactoryMethod = constructorToUse;
        }
        catch (Throwable ex) {
          throw new BeanInstantiationException(clazz, "No default constructor found", ex);
        }
      }
    }               
    //使用構(gòu)造方法進(jìn)行實(shí)例化
    return BeanUtils.instantiateClass(constructorToUse);
  }
  else {
    //使用CGLIB進(jìn)行實(shí)例化
    return instantiateWithMethodInjection(bd, beanName, owner);
  }
}

//設(shè)置構(gòu)造方法為可訪問
ReflectionUtils.makeAccessible(ctor);
//反射創(chuàng)建對象
return (KotlinDetector.isKotlinType(ctor.getDeclaringClass()) ?
   KotlinDelegate.instantiateClass(ctor, args) : ctor.newInstance(args));