Spring BeanFacoty doCreateBean方法分析

上一篇,我们分析到了doCreateBean,现在继续:

先看看时序图

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
		// Instantiate the bean.
		BeanWrapper instanceWrapper = null;
		if (mbd.isSingleton()) {
			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
		}
		if (instanceWrapper == null) {
			//*************************5.4.1
			instanceWrapper = createBeanInstance(beanName, mbd, args);
		}
		final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
		Class beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);

		// Allow post-processors to modify the merged bean definition.
		//*************************5.4.2
		synchronized (mbd.postProcessingLock) {
			if (!mbd.postProcessed) {
				applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
				mbd.postProcessed = true;
			}
		}

		// Eagerly cache singletons to be able to resolve circular references
		// even when triggered by lifecycle interfaces like BeanFactoryAware.
		//*************************5.4.3 处理循环依赖的问题
		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, new ObjectFactory() {
				public Object getObject() throws BeansException {
					return getEarlyBeanReference(beanName, mbd, bean);
				}
			});
		}

		// Initialize the bean instance.
		Object exposedObject = bean;
		try {
			//*************************5.4.4 将mdb中的值放到instanceWrapper中
			populateBean(beanName, mbd, instanceWrapper);
			if (exposedObject != null) {
				//*************************5.4.5 正儿八经的初始化
				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);
			}
		}

		//似乎还是循环依赖的问题
		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<String>(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 {
			//*************************5.4.6 注册销毁方法
			registerDisposableBeanIfNecessary(beanName, bean, mbd);
		}
		catch (BeanDefinitionValidationException ex) {
			throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
		}

		return exposedObject;
	}

在5.4.1处

首先判断是否有factory-method属性

即:

<bean id="bar" class="...StaticBarInterfaceFactory" factory-method="getInstance"/> 

如果有就直接通过工厂方法生产之。 参见 拙作spring中工厂方法 http://blog.csdn.net/dlf123321/article/details/47856937#t6

如果没有有默认的构造方法,且bean中包含constructor-arg

<bean id="newsBean3" class="com.luhy.spring.hello.FXNewsBean" scope="singleton">
	<constructor-arg>
		<value>This is a configurable message</value>
	</constructor-arg>
</bean> 

就调用默认的含参构造方法。

否则调用instantiateBean

AbstractAutowireCapableBeanFactory.java
	protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
		try {
			Object beanInstance;
			final BeanFactory parent = this;
			if (System.getSecurityManager() != null) {
				beanInstance = AccessController.doPrivileged(new PrivilegedAction<Object>() {
					public Object run() {
						return getInstantiationStrategy().instantiate(mbd, beanName, parent);
					}
				}, getAccessControlContext());
			}
			else {
				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);
		}
	}

我们在AbstractAutowireCapableBeanFactory里可以看到

/** Strategy for creating bean instances */
private InstantiationStrategy instantiationStrategy = new CglibSubclassingInstantiationStrategy();
getInstantiationStrategy()返回的是InstantiationStrategy接口的实现类,默认是CglibSubclassingInstantiationStrategy。

通过cglib生成实例对象。

至5.4.1,BeanWrapper的生成基本清晰了。





5.4.2处是允许其他修改beanDefinition，这主要是允许其他组件提供xml不能提供的信息。如使用Annotation增强Bean定义等。这通过类ergedBeanDefinitionPostProcessor来完成，如果容器中提供了此类实现，则会调用进行bean增强。如CommonAnnotationBeanPostProcessor类，会在bean定义中追加如 @Resource之类的bean property引用信息。此代码如下所示：

	protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class beanType, String beanName)
			throws BeansException {

		try {
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				if (bp instanceof MergedBeanDefinitionPostProcessor) {
					MergedBeanDefinitionPostProcessor bdp = (MergedBeanDefinitionPostProcessor) bp;
					bdp.postProcessMergedBeanDefinition(mbd, beanType, beanName);
				}
			}
		}
		catch (Exception ex) {
			throw new BeanCreationException(mbd.getResourceDescription(), beanName,
					"Post-processing failed of bean type [" + beanType + "] failed", ex);
		}
	}

在5.4.3处,关于循环依赖问题,可以参考 http://www.iflym.com/index.php/code/201208280001.html





在5.4.4处populateBean(String beanName, AbstractBeanDefinition mbd, BeanWrapper bw)

说实话,我第一回看到这方法的时候,populate,流行的?流行的bean? 呵呵,见笑了。

在populate里面

     

  /**
	 * Populate the bean instance in the given BeanWrapper with the property values
	 * from the bean definition.
	 * @param beanName the name of the bean
	 * @param mbd the bean definition for the bean
	 * @param bw BeanWrapper with bean instance
	 */
	protected void populateBean(String beanName, AbstractBeanDefinition mbd, BeanWrapper bw) {
		PropertyValues pvs = mbd.getPropertyValues();

		if (bw == null) {
			if (!pvs.isEmpty()) {
				throw new BeanCreationException(
						mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
			}
			else {
				// Skip property population phase for null instance.
				return;
			}
		}

		// Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
		// state of the bean before properties are set. This can be used, for example,
		// to support styles of field injection.
		//*******************5.4.4.1
		boolean continueWithPropertyPopulation = true;

		if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				if (bp instanceof InstantiationAwareBeanPostProcessor) {
					InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
					if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
						continueWithPropertyPopulation = false;
						break;
					}
				}
			}
		}

		if (!continueWithPropertyPopulation) {
			return;
		}

		//*******************5.4.4.2
		if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
				mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
			MutablePropertyValues newPvs = new MutablePropertyValues(pvs);

			// Add property values based on autowire by name if applicable.
			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
				autowireByName(beanName, mbd, bw, newPvs);
			}

			// Add property values based on autowire by type if applicable.
			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
				autowireByType(beanName, mbd, bw, newPvs);
			}

			pvs = newPvs;
		}

		boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
		boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);

		//*******************5.4.4.3
		if (hasInstAwareBpps || needsDepCheck) {
			PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw);
			if (hasInstAwareBpps) {
				for (BeanPostProcessor bp : getBeanPostProcessors()) {
					if (bp instanceof InstantiationAwareBeanPostProcessor) {
						InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
						pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
						if (pvs == null) {
							return;
						}
					}
				}
			}
			if (needsDepCheck) {
				checkDependencies(beanName, mbd, filteredPds, pvs);
			}
		}
		//*******************5.4.4.4
		applyPropertyValues(beanName, mbd, bw, pvs);
	}

好长呀,慢慢来,这里大概可以分为4部分

首先5.4.4.1

如果所要获取的bean实现了InstantiationAwareBeanPostProcessor接口,就调用其postProcessAfterInstantiation方法。

<span style="white-space:pre">		</span>// Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
		// state of the bean before properties are set. This can be used, for example,
		// to support styles of field injection.
		boolean continueWithPropertyPopulation = true;

		if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				if (bp instanceof InstantiationAwareBeanPostProcessor) {
					InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
					if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
						continueWithPropertyPopulation = false;
						break;
					}
				}
			}
		}

		if (!continueWithPropertyPopulation) {
			return;
		}

多说几句,postProcessAfterInstantiation的返回值是一个boolean,如果返回值是false,就说明已经属性处理已经结束了。后面的代码就不运行了。

接着5.4.4.2

if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
				mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
			MutablePropertyValues newPvs = new MutablePropertyValues(pvs);

			// Add property values based on autowire by name if applicable.
			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
				autowireByName(beanName, mbd, bw, newPvs);
			}

			// Add property values based on autowire by type if applicable.
			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
				autowireByType(beanName, mbd, bw, newPvs);
			}

			pvs = newPvs;
		}

不需要解释了吧,就是处理autowire标签。





再然后5.4.4.3

给InstantiationAwareBeanPostProcessor机会以处理属性信息，比如在xml中描述了Annotation定义，使用了<context:annotation-config/>，那么就会使用类CommonAnnotationBeanPostProcessor进行注解类属性注入。如下代码所示：

if (hasInstAwareBpps || needsDepCheck) {
			PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw);
			if (hasInstAwareBpps) {
				for (BeanPostProcessor bp : getBeanPostProcessors()) {
					if (bp instanceof InstantiationAwareBeanPostProcessor) {
						InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
						pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
						if (pvs == null) {
							return;
						}
					}
				}
			}
			if (needsDepCheck) {
				checkDependencies(beanName, mbd, filteredPds, pvs);
			}
		}

我们看下面的解释:





最后5.4.4.4

applyPropertyValues(beanName, mbd, bw, pvs)干的事情就是填充值。

这里都干了什么事情,我举个例子。

<bean id="newsBean2" class="com.luhy.spring.hello.FXNewsBean" scope="prototype">
      <property name="p">
  	 <value>dlf</value>
      </property>
</bean> 

com.luhy.spring.hello.FXNewsBean中p这个属性是一个Person。

如何将字符串"dlf"(在xml中,所有的信息不都是字符么)转换为person呢?

我们需要下面这个类:

public class PersonEditor extends PropertyEditorSupport {
	@Override
	public void setAsText(String text) throws IllegalArgumentException {
		Person p = new Person();
		p.setName(text);
		System.out.println("setAsTest");
		setValue(p);
	}
}

那么什么时候调用这个PersonEditor呢?就在5.4.5.4的applyPropertyValues里。

当然,这里我只是举个例子。这里还包括集合类型的转换,基本类型的转换等等。

关于类型转换参见 http://blog.csdn.net/dlf123321/article/details/47905533#t3

关于5.4.5

protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
		if (System.getSecurityManager() != null) {
			AccessController.doPrivileged(new PrivilegedAction<Object>() {
				public Object run() {
					invokeAwareMethods(beanName, bean);
					return null;
				}
			}, getAccessControlContext());
		}
		else {
			//处理XXAware接口的实现
                        //beanFactoryAware这这个处理
			invokeAwareMethods(beanName, bean);
		}

		Object wrappedBean = bean;
		if (mbd == null || !mbd.isSynthetic()) {
			//处理postProcessBeforeInitialization
<span style="white-space:pre">			</span>//在这里处理ApplicationContextAware(使用ApplicationContextAwareProcessor)
			wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
		}

		try {
			//这里面调用了 InitializingBean的afterPropertiesSet
			//同时还有init-method指定的方法
			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()) {
			//postProcessAfterInitialization方法
			wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
		}
		return wrappedBean;
	}

总结一下初始化顺序

 XXAware接口的实现->postProcessBeforeInitialization->InitializingBean的afterPropertiesSet-> custom Init方法->postProcessAfterInitialization

  OK.这就是bean初始化的顺序啦！





5.4.6注册销毁方法

至此,获取对象完毕。

参考资料

http://blog.csdn.net/dlf123321/article/details/47856937#t6 spring中工厂方法

http://www.iflym.com/index.php/code/201208280001.html 循环引用

http://www.iflym.com/index.php/code/201208290001.html Spring中获取一个bean的流程-1

http://michael-softtech.iteye.com/blog/816469     spring源码分析之——spring bean的获取

http://blog.csdn.net/dlf123321/article/details/47905533#t3  关于类型转换

http://blog.csdn.net/zhoudaxia/article/details/36247883#t5   关于类型转换