Spring源码分析-Bean生命周期createBean

Spring源码分析-启动流程浅析
Spring源码分析-BeanDefinition
Spring源码分析-Bean管理查找与注册(1)
Spring源码分析-Bean管理查找与注册(2)
Spring源码分析-Bean管理循环依赖和三级缓存
Spring源码分析-Bean生命周期概述
Spring源码分析-Bean生命周期createBean

Spring源码分析系列前言一、bean创建流程二、doCreateBean三、总结

bean的生命周期状态虽然比较多，但是通过梳理代码其实也不是那么复杂。再次回顾bean的生命周期：
实例化 -->属性赋值–> bean后置处理器的before方法 --> 属性后置处理afterPropertiesSet --> bean初始化过程 --> bean后置处理器的after方法 --> 对象应用 --> bean销毁过程 --> gc回收

通过流程图来，bean的创建流程也不太复杂啊

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

	// Instantiate the bean.
	BeanWrapper instanceWrapper = null;
	if (mbd.isSingleton()) {
		instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
	}
	if (instanceWrapper == null) {
		instanceWrapper = createBeanInstance(beanName, mbd, args); // 创建bean实例
	}
	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.isTraceEnabled()) {
			logger.trace("Eagerly caching bean '" + beanName +
					"' to allow for resolving potential circular references");
		}
		//先放到 三级缓存 中 这个地方是lambda表达
		//三级缓存
		addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));

		
		//Object targetBean = getEarlyBeanReference(beanName, mbd, bean);
		//earlySingletonObjects.put(beanName, targetBean); //添加二级缓存
		//registeredSingletons.add(beanName);
	}

	// Initialize the bean instance.
	Object exposedObject = bean;
	try {
		//属性赋值
		populateBean(beanName, mbd, instanceWrapper);
		//执行后置处理器BeanPostProcessor,  如果动态代理场景 则返回的是动态代理对象
		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) {
		// 这里是false，只查询一级缓存，二级缓存，不查三级缓存
		Object earlySingletonReference = getSingleton(beanName, false);
		if (earlySingletonReference != null) {
			if (exposedObject == bean) {
				exposedObject = earlySingletonReference;
			}
			else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
				String[] dependentBeans = getDependentBeans(beanName);
				Set 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 " +
							"'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");
				}
			}
		}
	}

	// Register bean as disposable.
	// 注册析构回调
	try {
		registerDisposableBeanIfNecessary(beanName, bean, mbd);
	}
	catch (BeanDefinitionValidationException ex) {
		throw new BeanCreationException(
				mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
	}
	return exposedObject;
}

主要是流程图，代码逻辑不复杂，这里不再介绍，大家可按照流程图翻看源码。