Spring源码(3) Spring IoC之BeanFactory创建bean和获取bean

ApplicationContext 和 BeanFactory

可以先简单了解下 ApplicationContext 和 BeanFactory。

详情见： https://blog.csdn.net/sinat_32502451/article/details/140247662

getBean() 代码示例

首先看代码示例，调试一下。

代码详情见： https://blog.csdn.net/sinat_32502451/article/details/140155044

public class MySpring {

    public static void main(String[] args) {
        ApplicationContext context =
                new ClassPathXmlApplicationContext("classpath*:mySpring.xml");
        //在 getBean 这一行，打个断点
        Person person = context.getBean("person", Person.class);
        System.out.println("=======>"+ person.getName());
    }

}

BeanFactory 的 getBean() 源码：

public interface BeanFactory {
	//根据 bean 的名称，返回 bean对象.
	Object getBean(String name) throws BeansException;
	
	//根据 bean 名称，以及 匹配bean的类型，返回 bean对象.
	<T> T getBean(String name, @Nullable Class<T> requiredType) throws BeansException;

	Object getBean(String name, Object... args) throws BeansException;

	<T> T getBean(Class<T> requiredType) throws BeansException;

	<T> T getBean(Class<T> requiredType, Object... args) throws BeansException;

}	

bean 的作用域：

BeanFactory 中这两个方法，用于判断 bean 的作用域。

	//作用域是否为单例模式？如果是， 每次调用 getBean()方法都会返回同一个对象。
	boolean isSingleton(String name) throws NoSuchBeanDefinitionException;

	//作用域是否为原型模式？如果是， 每次调用 getBean()方法都会返回不同的对象。
	boolean isPrototype(String name) throws NoSuchBeanDefinitionException;

bean 对象的三级缓存：

bean 对象主要放在 map 里面，map 作为缓存。map 的key 是 bean对象的名称， value 是 bean 对象或者对象工厂。

Spring 使用了 三级缓存。

详情见：org.springframework.beans.factory.support.DefaultSingletonBeanRegistry

	/** 第一级缓存，里面放置的是已经实例化好的单例对象 */
	private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);

	/** 第二级缓存，里面存放的是提前曝光的单例对象 */
	private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<>(16);

	/** 第三级缓存，里面存放的是将要被实例化的对象的对象工厂 */
	private final Map<String, Object> earlySingletonObjects = new HashMap<>(16);

添加 bean 对象到缓存中 :

• 创建 bean 对象，添加 到缓存的具体方法：

重点看下这几个方法。

org.springframework.context.support.AbstractApplicationContext#refresh

----> org.springframework.context.support.AbstractApplicationContext#finishBeanFactoryInitialization

----> org.springframework.beans.factory.support.DefaultListableBeanFactory#preInstantiateSingletons

----> org.springframework.beans.factory.support.AbstractBeanFactory#getBean(java.lang.String)

----> org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean

----> org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String, org.springframework.beans.factory.ObjectFactory<?>)

接下来会 实例化bean ：

-----> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#createBean(java.lang.String, org.springframework.beans.factory.support.RootBeanDefinition, java.lang.Object[])

-----> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#doCreateBean

初始化 bean：

-----> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#initializeBean(java.lang.String, java.lang.Object, org.springframework.beans.factory.support.RootBeanDefinition)

添加 bean 对象到缓存：

----> org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#addSingleton

获取 bean对象：

----> org.springframework.beans.factory.support.AbstractBeanFactory#getBean(java.lang.String)

----> org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean

----> org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String, org.springframework.beans.factory.ObjectFactory<?>)

可以看到 实例化bean 、初始化 bean、 获取 bean对象， 都调用了 getBean() 方法。

getBean() 的具体实现：

重点看 getSingleton() 方法 和 createBean() 方法。

	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;

		// 检查单例缓存中是否有手动注册的单例
		Object sharedInstance = getSingleton(beanName);
		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);
		}

		else {
			// 如果我们已经在创建这个bean实例，则失败
			// We're assumably within a circular reference.
			if (isPrototypeCurrentlyInCreation(beanName)) {
				throw new BeanCurrentlyInCreationException(beanName);
			}

			//检查此工厂中是否存在bean定义
			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) {
				markBeanAsCreated(beanName);
			}

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

				// 保证初始化当前bean所依赖的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 + "'");
						}
						registerDependentBean(dep, beanName);
						try {
							getBean(dep);
						}
						catch (NoSuchBeanDefinitionException ex) {
							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
									"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
						}
					}
				}

				// 判断是否单例模式
				if (mbd.isSingleton()) {
					//获取单例模式的 bean，并添加到缓存中。这里可以重点看看。
					sharedInstance = getSingleton(beanName, () -> {
						try {
							//创建bean实例。。重点看看。
							return createBean(beanName, mbd, args);
						}
						catch (BeansException ex) {
							// 从单例缓存中删除实例
							destroySingleton(beanName);
							throw ex;
						}
					});
					bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
				}

				else if (mbd.isPrototype()) {
					// 如果是原型模式，就创建一个新的实例
					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;
			}
		}

		// 检查所需的类型是否与实际bean实例的类型匹配
		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;
	}

创建 bean 对象：

关键看 实例化 bean 、 初始化 bean 。

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

		BeanWrapper instanceWrapper = null;
		if (mbd.isSingleton()) {
			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
		}
		if (instanceWrapper == null) {
			instanceWrapper = createBeanInstance(beanName, mbd, args);
		}
		// 实例化 bean。 核心。
		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;
			}
		}

		// Eagerly cache singletons to be able to resolve circular references
		// even when triggered by lifecycle interfaces like BeanFactoryAware.
		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");
			}
			addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
		}

		Object exposedObject = bean;
		try {
			populateBean(beanName, mbd, instanceWrapper);
            // 初始化bean。。核心。重点看看。
			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,
								"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.");
					}
				}
			}
		}

		// Register bean as disposable.
		try {
			registerDisposableBeanIfNecessary(beanName, bean, mbd);
		}
		catch (BeanDefinitionValidationException ex) {
			throw new BeanCreationException(
					mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
		}

		return exposedObject;
	}

初始化bean：

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

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

		try {
			invokeInitMethods(beanName, wrappedBean, mbd);
		}
		catch (Throwable ex) {
			throw new BeanCreationException(
					(mbd != null ? mbd.getResourceDescription() : null),
					beanName, "Invocation of init method failed", ex);
		}
		if (mbd == null || !mbd.isSynthetic()) {
			wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
		}

		return wrappedBean;
	}

• 获取单例对象：

根据 bean 名称，返回已经注册的单例对象，

如果没有注册，则创建并注册一个新对象。

/**
  *   根据 bean 名称，返回已经注册的单例对象，如果没有注册，则创建并注册一个新对象。
  */ 
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
   Assert.notNull(beanName, "Bean name must not be null");
   //加同步锁
   synchronized (this.singletonObjects) {
   	  //根据 bean 名称，返回已经注册的单例对象
      Object singletonObject = this.singletonObjects.get(beanName);
      if (singletonObject == null) {
         if (this.singletonsCurrentlyInDestruction) {
            throw new BeanCreationNotAllowedException(beanName,
                  "Singleton bean creation not allowed while singletons of this factory are in destruction " +
                  "(Do not request a bean from a BeanFactory in a destroy method implementation!)");
         }
         if (logger.isDebugEnabled()) {
            logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
         }
         beforeSingletonCreation(beanName);
         boolean newSingleton = false;
         boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
         if (recordSuppressedExceptions) {
            this.suppressedExceptions = new LinkedHashSet<>();
         }
         try {
            singletonObject = singletonFactory.getObject();
            newSingleton = true;
         }
         catch (IllegalStateException ex) {
            singletonObject = this.singletonObjects.get(beanName);
            if (singletonObject == null) {
               throw ex;
            }
         }
         catch (BeanCreationException ex) {
            if (recordSuppressedExceptions) {
               for (Exception suppressedException : this.suppressedExceptions) {
                  ex.addRelatedCause(suppressedException);
               }
            }
            throw ex;
         }
         finally {
            if (recordSuppressedExceptions) {
               this.suppressedExceptions = null;
            }
            afterSingletonCreation(beanName);
         }
         //这一块可以重点看下。 判断是否新的单例对象。
         if (newSingleton) {
         	//前面介绍过， 如果是新的单例对象，此处将 bean 添加到 缓存中
            addSingleton(beanName, singletonObject);
         }
      }
      return singletonObject;
   }
}

• addSingleton() 方法：

如下， 将 bean 添加到 缓存中 ：

	protected void addSingleton(String beanName, Object singletonObject) {
		synchronized (this.singletonObjects) {
			//添加到缓存中。beanName值类似 上面的对象名"person" 
			//singletonObject类似具体的对象 Person(age=1, name=Tom, fullName=null, dateOfBirth=null)
			this.singletonObjects.put(beanName, singletonObject);
			this.singletonFactories.remove(beanName);
			this.earlySingletonObjects.remove(beanName);
			this.registeredSingletons.add(beanName);
		}
	}