当应用程序含有事务管理时,xmlApplicationContext的调试

读取通知配置的类是:TxAdviceBeanDefinitionParser。
这个类将xml中配置的通知标签读取到bean定义中去,也就是将事务属性读取到bean定义中。

	
	<tx:advice id="tx-advice">
		
		<tx:attributes>
			
			<tx:method name="add*" propagation="REQUIRED" isolation="DEFAULT" read-only="false" timeout="10"/>
		tx:attributes>
	tx:advice>

上面的配置读取到的bean定义实际是如下的TransactionInterceptor拦截器,如下图中的definition所示:
当应用程序含有事务管理时,xmlApplicationContext的调试_第1张图片
切点和切面的配置·读取,配置代码如下:


	<aop:config>
		
		<aop:pointcut id="tx-pt" expression="execution(* org.springframework.service.UserServiceImpl.*(..))"/>
		
		<aop:advisor advice-ref="tx-advice" pointcut-ref="tx-pt">aop:advisor>
	aop:config>

首先根据xml的命名空间获取对应的处理器:

public BeanDefinition parseCustomElement(Element ele, @Nullable BeanDefinition containingBd) {
		String namespaceUri = getNamespaceURI(ele);
		if (namespaceUri == null) {
			return null;
		}
		NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
		if (handler == null) {
			error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
			return null;
		}
		return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
	}

这里获取到的handler是一个AopNamespaceHandler,如下:
当应用程序含有事务管理时,xmlApplicationContext的调试_第2张图片
实际的解析,还需要调用NamespaceHandlerSupport的findParserForElement方法获取解析器:

@Override
	@Nullable
	public BeanDefinition parse(Element element, ParserContext parserContext) {
		BeanDefinitionParser parser = findParserForElement(element, parserContext);
		return (parser != null ? parser.parse(element, parserContext) : null);
	}

最终进行解析的类是ConfigBeanDefinitionParser,这个类解析的是aop的配置信息,
当应用程序含有事务管理时,xmlApplicationContext的调试_第3张图片
配置自动代理创建器:

/**
	 * Configures the auto proxy creator needed to support the {@link BeanDefinition BeanDefinitions}
	 * created by the '{@code }' tag. Will force class proxying if the
	 * '{@code proxy-target-class}' attribute is set to '{@code true}'.
	 * @see AopNamespaceUtils
	 */
	private void configureAutoProxyCreator(ParserContext parserContext, Element element) {
		AopNamespaceUtils.registerAspectJAutoProxyCreatorIfNecessary(parserContext, element);
	}
	//一下是注册自动代理创建器的方法
public static void registerAspectJAutoProxyCreatorIfNecessary(
			ParserContext parserContext, Element sourceElement) {

		BeanDefinition beanDefinition = AopConfigUtils.registerAspectJAutoProxyCreatorIfNecessary(
				parserContext.getRegistry(), parserContext.extractSource(sourceElement));
		useClassProxyingIfNecessary(parserContext.getRegistry(), sourceElement);
		registerComponentIfNecessary(beanDefinition, parserContext);
	}

当应用程序含有事务管理时,xmlApplicationContext的调试_第4张图片

private static BeanDefinition registerOrEscalateApcAsRequired(
			Class<?> cls, BeanDefinitionRegistry registry, @Nullable Object source) {

		Assert.notNull(registry, "BeanDefinitionRegistry must not be null");

		if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {
			BeanDefinition apcDefinition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);
			if (!cls.getName().equals(apcDefinition.getBeanClassName())) {
				int currentPriority = findPriorityForClass(apcDefinition.getBeanClassName());
				int requiredPriority = findPriorityForClass(cls);
				if (currentPriority < requiredPriority) {
					apcDefinition.setBeanClassName(cls.getName());
				}
			}
			return null;
		}

		RootBeanDefinition beanDefinition = new RootBeanDefinition(cls);
		beanDefinition.setSource(source);
		beanDefinition.getPropertyValues().add("order", Ordered.HIGHEST_PRECEDENCE);
		beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
		registry.registerBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME, beanDefinition);
		return beanDefinition;
	}

上述方法将注册名为:org.springframework.aop.config.internalAutoProxyCreator 的自动代理创建器。
注册配置了自动代理创建器之后,ConfigBeanDefinition的parse方法将读取aop-config的其它属性配置,如切点,通知和切面。
如下图进入解析pointcut切点的代码:
当应用程序含有事务管理时,xmlApplicationContext的调试_第5张图片
切点对应的类是: AspectJExpressionPointcut

需要注意的是这是一个原型类:
当应用程序含有事务管理时,xmlApplicationContext的调试_第6张图片
上述方法将切点bean定义注册到容器。

然后是解析aop-config标签的’通知’元素:
当应用程序含有事务管理时,xmlApplicationContext的调试_第7张图片
解析通知的方法如下:

private void parseAdvisor(Element advisorElement, ParserContext parserContext) {
		AbstractBeanDefinition advisorDef = createAdvisorBeanDefinition(advisorElement, parserContext);
		String id = advisorElement.getAttribute(ID);

		try {
			this.parseState.push(new AdvisorEntry(id));
			String advisorBeanName = id;
			if (StringUtils.hasText(advisorBeanName)) {
				parserContext.getRegistry().registerBeanDefinition(advisorBeanName, advisorDef);
			}
			else {
				advisorBeanName = parserContext.getReaderContext().registerWithGeneratedName(advisorDef);
			}

			Object pointcut = parsePointcutProperty(advisorElement, parserContext);
			if (pointcut instanceof BeanDefinition) {
				advisorDef.getPropertyValues().add(POINTCUT, pointcut);
				parserContext.registerComponent(
						new AdvisorComponentDefinition(advisorBeanName, advisorDef, (BeanDefinition) pointcut));
			}
			else if (pointcut instanceof String) {
				advisorDef.getPropertyValues().add(POINTCUT, new RuntimeBeanReference((String) pointcut));
				parserContext.registerComponent(
						new AdvisorComponentDefinition(advisorBeanName, advisorDef));
			}
		}
		finally {
			this.parseState.pop();
		}
	}

创建通知器bean定义的代码如下:

private AbstractBeanDefinition createAdvisorBeanDefinition(Element advisorElement, ParserContext parserContext) {
		RootBeanDefinition advisorDefinition = new RootBeanDefinition(DefaultBeanFactoryPointcutAdvisor.class);
		advisorDefinition.setSource(parserContext.extractSource(advisorElement));

		String adviceRef = advisorElement.getAttribute(ADVICE_REF);
		if (!StringUtils.hasText(adviceRef)) {
			parserContext.getReaderContext().error(
					"'advice-ref' attribute contains empty value.", advisorElement, this.parseState.snapshot());
		}
		else {
			advisorDefinition.getPropertyValues().add(
					ADVICE_BEAN_NAME, new RuntimeBeanNameReference(adviceRef));
		}

		if (advisorElement.hasAttribute(ORDER_PROPERTY)) {
			advisorDefinition.getPropertyValues().add(
					ORDER_PROPERTY, advisorElement.getAttribute(ORDER_PROPERTY));
		}

		return advisorDefinition;
	}

上述代码会读取通知引用,然后设置到通知器的属性“adviceBeanName”中去。

由于我们没有未通知命名,框架会自动生成一个名字:
当应用程序含有事务管理时,xmlApplicationContext的调试_第8张图片
parsePointcutProperty解析通知的切点属性:

private Object parsePointcutProperty(Element element, ParserContext parserContext) {
		if (element.hasAttribute(POINTCUT) && element.hasAttribute(POINTCUT_REF)) {
			parserContext.getReaderContext().error(
					"Cannot define both 'pointcut' and 'pointcut-ref' on  tag.",
					element, this.parseState.snapshot());
			return null;
		}
		else if (element.hasAttribute(POINTCUT)) {
			// Create a pointcut for the anonymous pc and register it.
			String expression = element.getAttribute(POINTCUT);
			AbstractBeanDefinition pointcutDefinition = createPointcutDefinition(expression);
			pointcutDefinition.setSource(parserContext.extractSource(element));
			return pointcutDefinition;
		}
		else if (element.hasAttribute(POINTCUT_REF)) {
			String pointcutRef = element.getAttribute(POINTCUT_REF);
			if (!StringUtils.hasText(pointcutRef)) {
				parserContext.getReaderContext().error(
						"'pointcut-ref' attribute contains empty value.", element, this.parseState.snapshot());
				return null;
			}
			return pointcutRef;
		}
		else {
			parserContext.getReaderContext().error(
					"Must define one of 'pointcut' or 'pointcut-ref' on  tag.",
					element, this.parseState.snapshot());
			return null;
		}
	}

完成bean的定义读取之后,在容器里有以下bean定义:
当应用程序含有事务管理时,xmlApplicationContext的调试_第9张图片
回到AbstractApplicationContext类的refresh方法,
当应用程序含有事务管理时,xmlApplicationContext的调试_第10张图片
在refresh方法的registerBeanPostProcessors方法中调用PostProcessorRegistrationDelegate的方法注册后处理器,如下:

public static void registerBeanPostProcessors(
			ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

		// WARNING: Although it may appear that the body of this method can be easily
		// refactored to avoid the use of multiple loops and multiple lists, the use
		// of multiple lists and multiple passes over the names of processors is
		// intentional. We must ensure that we honor the contracts for PriorityOrdered
		// and Ordered processors. Specifically, we must NOT cause processors to be
		// instantiated (via getBean() invocations) or registered in the ApplicationContext
		// in the wrong order.
		//
		// Before submitting a pull request (PR) to change this method, please review the
		// list of all declined PRs involving changes to PostProcessorRegistrationDelegate
		// to ensure that your proposal does not result in a breaking change:
		// https://github.com/spring-projects/spring-framework/issues?q=PostProcessorRegistrationDelegate+is%3Aclosed+label%3A%22status%3A+declined%22

		String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

		// Register BeanPostProcessorChecker that logs an info message when
		// a bean is created during BeanPostProcessor instantiation, i.e. when
		// a bean is not eligible for getting processed by all BeanPostProcessors.
		int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
		beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

		// Separate between BeanPostProcessors that implement PriorityOrdered,
		// Ordered, and the rest.
		List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
		List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
		List<String> orderedPostProcessorNames = new ArrayList<>();
		List<String> nonOrderedPostProcessorNames = new ArrayList<>();
		for (String ppName : postProcessorNames) {
			if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
				BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
				priorityOrderedPostProcessors.add(pp);
				if (pp instanceof MergedBeanDefinitionPostProcessor) {
					internalPostProcessors.add(pp);
				}
			}
			else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
				orderedPostProcessorNames.add(ppName);
			}
			else {
				nonOrderedPostProcessorNames.add(ppName);
			}
		}

		// First, register the BeanPostProcessors that implement PriorityOrdered.
		sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
		registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

		// Next, register the BeanPostProcessors that implement Ordered.
		List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
		for (String ppName : orderedPostProcessorNames) {
			BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
			orderedPostProcessors.add(pp);
			if (pp instanceof MergedBeanDefinitionPostProcessor) {
				internalPostProcessors.add(pp);
			}
		}
		sortPostProcessors(orderedPostProcessors, beanFactory);
		registerBeanPostProcessors(beanFactory, orderedPostProcessors);

		// Now, register all regular BeanPostProcessors.
		List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
		for (String ppName : nonOrderedPostProcessorNames) {
			BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
			nonOrderedPostProcessors.add(pp);
			if (pp instanceof MergedBeanDefinitionPostProcessor) {
				internalPostProcessors.add(pp);
			}
		}
		registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

		// Finally, re-register all internal BeanPostProcessors.
		sortPostProcessors(internalPostProcessors, beanFactory);
		registerBeanPostProcessors(beanFactory, internalPostProcessors);

		// Re-register post-processor for detecting inner beans as ApplicationListeners,
		// moving it to the end of the processor chain (for picking up proxies etc).
		beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
	}

在上面的中可以看到调用beanFactory的getBean方法,这里会创建后处理器postProcessor。

创建代理bean

事务代理bean的创建,在AbstractAutowireCapableBeanFactory类的protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException 方法中,调用:

		protected Object initializeBean(String beanName, 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;
	}

上述方法中applyBeanPostProcessorsAfterInitialization方法会为事务bean创建代理,创建代理的处理器就是在aop配置中配置的bean:

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

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

调用的是AbstractAutoProxyCreator的以下方法:

public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
		if (bean != null) {
			Object cacheKey = getCacheKey(bean.getClass(), beanName);
			if (this.earlyProxyReferences.remove(cacheKey) != bean) {
				return wrapIfNecessary(bean, beanName, cacheKey);
			}
		}
		return bean;
	}

在warpIfNecessary中创建代理对象。

protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
		if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
			return bean;
		}
		if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
			return bean;
		}
		if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
			this.advisedBeans.put(cacheKey, Boolean.FALSE);
			return bean;
		}

		// Create proxy if we have advice.
		Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
		if (specificInterceptors != DO_NOT_PROXY) {
			this.advisedBeans.put(cacheKey, Boolean.TRUE);
			Object proxy = createProxy(
					bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
			this.proxyTypes.put(cacheKey, proxy.getClass());
			return proxy;
		}

		this.advisedBeans.put(cacheKey, Boolean.FALSE);
		return bean;
	}

这个wrapIfNecessary会调用getAdvicesAndAdvisorsForBean,获取对应bean的通知,在这个过程中会创建通知,具体的是TransactionInterceptor实例。在创建这个拦截器实例的过程中,有一系列的匹配方法来确定这个bean是否有对应的拦截器。

Eligible:符合条件的

在后处理器中,对每一个bean,代理创建器会在后置处理器方法中判断当前类是否配置了通知,具体的匹配过程比较复杂,最终调用的方法如下(在AopUtils类中):

public static boolean canApply(Pointcut pc, Class<?> targetClass, boolean hasIntroductions) {
		Assert.notNull(pc, "Pointcut must not be null");
		if (!pc.getClassFilter().matches(targetClass)) {
			return false;
		}

		MethodMatcher methodMatcher = pc.getMethodMatcher();
		if (methodMatcher == MethodMatcher.TRUE) {
			// No need to iterate the methods if we're matching any method anyway...
			return true;
		}

		IntroductionAwareMethodMatcher introductionAwareMethodMatcher = null;
		if (methodMatcher instanceof IntroductionAwareMethodMatcher) {
			introductionAwareMethodMatcher = (IntroductionAwareMethodMatcher) methodMatcher;
		}

		Set<Class<?>> classes = new LinkedHashSet<>();
		if (!Proxy.isProxyClass(targetClass)) {
			classes.add(ClassUtils.getUserClass(targetClass));
		}
		classes.addAll(ClassUtils.getAllInterfacesForClassAsSet(targetClass));

		for (Class<?> clazz : classes) {
			Method[] methods = ReflectionUtils.getAllDeclaredMethods(clazz);
			for (Method method : methods) {
				if (introductionAwareMethodMatcher != null ?
						introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions) :
						methodMatcher.matches(method, targetClass)) {
					return true;
				}
			}
		}

		return false;
	}

对于匹配上的通知,会创建拦截器,代码如下:
当应用程序含有事务管理时,xmlApplicationContext的调试_第11张图片
可以看到,拦截器的创建也是通过beanFactory的getBean方法创建的。

为上述txUserServiceImpl找到的两个通知器如下:
当应用程序含有事务管理时,xmlApplicationContext的调试_第12张图片
回到wrapIfNecessary方法,里面的createProxy方法,具体的是调用类AbstractAutoProxyCreator的aop代理创建方法:

/**
	 * Create an AOP proxy for the given bean.
	 * @param beanClass the class of the bean
	 * @param beanName the name of the bean
	 * @param specificInterceptors the set of interceptors that is
	 * specific to this bean (may be empty, but not null)
	 * @param targetSource the TargetSource for the proxy,
	 * already pre-configured to access the bean
	 * @return the AOP proxy for the bean
	 * @see #buildAdvisors
	 */
	protected Object createProxy(Class<?> beanClass, @Nullable String beanName,
			@Nullable Object[] specificInterceptors, TargetSource targetSource) {

		if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
			AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
		}

		ProxyFactory proxyFactory = new ProxyFactory();
		proxyFactory.copyFrom(this);

		if (proxyFactory.isProxyTargetClass()) {
			// Explicit handling of JDK proxy targets and lambdas (for introduction advice scenarios)
			if (Proxy.isProxyClass(beanClass) || ClassUtils.isLambdaClass(beanClass)) {
				// Must allow for introductions; can't just set interfaces to the proxy's interfaces only.
				for (Class<?> ifc : beanClass.getInterfaces()) {
					proxyFactory.addInterface(ifc);
				}
			}
		}
		else {
			// No proxyTargetClass flag enforced, let's apply our default checks...
			if (shouldProxyTargetClass(beanClass, beanName)) {
				proxyFactory.setProxyTargetClass(true);
			}
			else {
				evaluateProxyInterfaces(beanClass, proxyFactory);
			}
		}

		Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
		proxyFactory.addAdvisors(advisors);
		proxyFactory.setTargetSource(targetSource);
		customizeProxyFactory(proxyFactory);

		proxyFactory.setFrozen(this.freezeProxy);
		if (advisorsPreFiltered()) {
			proxyFactory.setPreFiltered(true);
		}

		// Use original ClassLoader if bean class not locally loaded in overriding class loader
		ClassLoader classLoader = getProxyClassLoader();
		if (classLoader instanceof SmartClassLoader && classLoader != beanClass.getClassLoader()) {
			classLoader = ((SmartClassLoader) classLoader).getOriginalClassLoader();
		}
		return proxyFactory.getProxy(classLoader);
	}

在上面的方法中有一个判断是代理类还是接口的逻辑。

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