Spring AOP事务01

    //TxNameSpaceHandler 
	public void init() {
		// springboot 使用 @EnableTransactionManagement
		// 读取tx:advice ，调用父级的注册方法注册解析器
		registerBeanDefinitionParser("advice", new TxAdviceBeanDefinitionParser());
		// 读取 xml 中 tx:annotation-dirvern   调用父级的注册方法注册解析器
		registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());
        /// 调用父级的注册方法注册解析器
		registerBeanDefinitionParser("jta-transaction-manager", new JtaTransactionManagerBeanDefinitionParser());
	}

    public BeanDefinition parse(Element element, ParserContext parserContext) {
		registerTransactionalEventListenerFactory(parserContext);
		/// 解析代理模式
		String mode = element.getAttribute("mode");
        /// <tx:annotation-driven transaction-manager="transactionManager" mode="aspectj"/>
		if ("aspectj".equals(mode)) {
			// mode="aspectj" 注册切面
			registerTransactionAspect(element, parserContext);
			if (ClassUtils.isPresent("javax.transaction.Transactional", getClass().getClassLoader())) {
				registerJtaTransactionAspect(element, parserContext);
			}
		}
		else {
			// mode="proxy"
			AopAutoProxyConfigurer.configureAutoProxyCreator(element, parserContext);
		}
		return null;
	}

    /**
	 * 注册切面
	 */
	private void registerTransactionAspect(Element element, ParserContext parserContext) {
		// org.springframework.transaction.config.internalTransactionAspect
		String txAspectBeanName = TransactionManagementConfigUtils.TRANSACTION_ASPECT_BEAN_NAME;
		// org.springframework.transaction.aspectj.AnnotationTransactionAspect
		String txAspectClassName = TransactionManagementConfigUtils.TRANSACTION_ASPECT_CLASS_NAME;
		if (!parserContext.getRegistry().containsBeanDefinition(txAspectBeanName)) {
			RootBeanDefinition def = new RootBeanDefinition();
			def.setBeanClassName(txAspectClassName);
			def.setFactoryMethodName("aspectOf");
			registerTransactionManager(element, def);
			parserContext.registerBeanComponent(new BeanComponentDefinition(def, txAspectBeanName));
		}
	}

public aspect AnnotationTransactionAspect extends AbstractTransactionAspect {

	public AnnotationTransactionAspect() {
		super(new AnnotationTransactionAttributeSource(false));
	}

	/**
	 * Matches the execution of any public method in a type with the Transactional
	 * annotation, or any subtype of a type with the Transactional annotation.
     * 查找所有带有@Transactional注解的或者子类中有的
	 */
	private pointcut executionOfAnyPublicMethodInAtTransactionalType() :
		execution(public * ((@Transactional *)+).*(..)) && within(@Transactional *);

	/**
	 * Matches the execution of any method with the Transactional annotation.
	 */
	private pointcut executionOfTransactionalMethod() :
		execution(@Transactional * *(..));

	/**
	 * Definition of pointcut from super aspect - matched join points
	 * will have Spring transaction management applied.
	 */
	protected pointcut transactionalMethodExecution(Object txObject) :
		(executionOfAnyPublicMethodInAtTransactionalType() || executionOfTransactionalMethod() ) && this(txObject);

}

public abstract aspect AbstractTransactionAspect extends TransactionAspectSupport implements DisposableBean {

	/**
	 * Construct the aspect using the given transaction metadata retrieval strategy.
	 * @param tas TransactionAttributeSource implementation, retrieving Spring
	 * transaction metadata for each joinpoint. Implement the subclass to pass in
	 * {@code null} if it is intended to be configured through Setter Injection.
	 */
	protected AbstractTransactionAspect(TransactionAttributeSource tas) {
		setTransactionAttributeSource(tas);
	}

	@Override
	public void destroy() {
        /// 调用 TransactionAspectSupport#clearTransactionManagerCache
		// An aspect is basically a singleton -> cleanup on destruction
		clearTransactionManagerCache();
	}

    /// 这个就是 @around注解要干的事情了
	@SuppressAjWarnings("adviceDidNotMatch")
	Object around(final Object txObject): transactionalMethodExecution(txObject) {
		MethodSignature methodSignature = (MethodSignature) thisJoinPoint.getSignature();
		// Adapt to TransactionAspectSupport's invokeWithinTransaction...
		try {
            /// 调用 TransactionAspectSupport 里面的 invokeWithinTransaction
			return invokeWithinTransaction(methodSignature.getMethod(), txObject.getClass(), new InvocationCallback() {
				public Object proceedWithInvocation() throws Throwable {
					return proceed(txObject);
				}
			});
		}
		catch (RuntimeException | Error ex) {
			throw ex;
		}
		catch (Throwable thr) {
			Rethrower.rethrow(thr);
			throw new IllegalStateException("Should never get here", thr);
		}
	}

	/**
	 * Concrete subaspects must implement this pointcut, to identify
	 * transactional methods. For each selected joinpoint, TransactionMetadata
	 * will be retrieved using Spring's TransactionAttributeSource interface.
	 */
	protected abstract pointcut transactionalMethodExecution(Object txObject);


	/**
	 * Ugly but safe workaround: We need to be able to propagate checked exceptions,
	 * despite AspectJ around advice supporting specifically declared exceptions only.
	 */
	private static class Rethrower {

		public static void rethrow(final Throwable exception) {
			class CheckedExceptionRethrower<T extends Throwable> {
				@SuppressWarnings("unchecked")
				private void rethrow(Throwable exception) throws T {
					throw (T) exception;
				}
			}
			new CheckedExceptionRethrower<RuntimeException>().rethrow(exception);
		}
	}

}

/*
    *  此方法主要作用是注册四个类到容器中 
    *  AnnotationTransactionAttributeSource 用于读取 @Transactional
    *  TransactionInterceptor  切面aspect
    *  BeanFactoryTransactionAttributeSourceAdvisor advisor 
    *  InfrastructureAdvisorAutoProxyCreator 用于创建代理对象
    */
public static void configureAutoProxyCreator(Element element, ParserContext parserContext) {
    // 向IOC注册 registerAutoProxyCreatorIfNecessary 这个类型的Bean  InfrastructureAdvisorAutoProxyCreator
    // 具体是在 AopConfigUtils 的 registerAutoProxyCreatorIfNecessary 方法中定义的 registerAutoProxyCreatorIfNecessary
    AopNamespaceUtils.registerAutoProxyCreatorIfNecessary(parserContext, element);
    // org.springframework.transaction.config.internalTransactionAdvisor
    String txAdvisorBeanName = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME;
    if (!parserContext.getRegistry().containsBeanDefinition(txAdvisorBeanName)) {
        Object eleSource = parserContext.extractSource(element);

        // Create the TransactionAttributeSource definition.
        /// 注册 TransactionAttributeSource
        RootBeanDefinition sourceDef = new RootBeanDefinition(
                "org.springframework.transaction.annotation.AnnotationTransactionAttributeSource");
        sourceDef.setSource(eleSource);
        sourceDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        String sourceName = parserContext.getReaderContext().registerWithGeneratedName(sourceDef);

        // Create the TransactionInterceptor definition.
        // 注册TransactionInterceptor
        RootBeanDefinition interceptorDef = new RootBeanDefinition(TransactionInterceptor.class);
        interceptorDef.setSource(eleSource);
        interceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        registerTransactionManager(element, interceptorDef);
        // 注入 AnnotationTransactionAttributeSource
        interceptorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
        String interceptorName = parserContext.getReaderContext().registerWithGeneratedName(interceptorDef);

        // Create the TransactionAttributeSourceAdvisor definition.
        // 注册 TransactionAttributeSourceAdvisor
        RootBeanDefinition advisorDef = new RootBeanDefinition(BeanFactoryTransactionAttributeSourceAdvisor.class);
        advisorDef.setSource(eleSource);
        advisorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        // 注入AnnotationTransactionAttributeSource，提供pointcut，切点
        advisorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
        // 注入TransactionInterceptor 的beanname
        advisorDef.getPropertyValues().add("adviceBeanName", interceptorName);
        if (element.hasAttribute("order")) {
            advisorDef.getPropertyValues().add("order", element.getAttribute("order"));
        }
        // 注册BeanFactoryTransactionAttributeSourceAdvisor BeanDefinition
        parserContext.getRegistry().registerBeanDefinition(txAdvisorBeanName, advisorDef);

        // 构建CompositeComponentDefinition完成以上Bean注册
        CompositeComponentDefinition compositeDef = new CompositeComponentDefinition(element.getTagName(), eleSource);
        compositeDef.addNestedComponent(new BeanComponentDefinition(sourceDef, sourceName));
        compositeDef.addNestedComponent(new BeanComponentDefinition(interceptorDef, interceptorName));
        compositeDef.addNestedComponent(new BeanComponentDefinition(advisorDef, txAdvisorBeanName));
        parserContext.registerComponent(compositeDef);
    }
}

// AbstractAutoProxyCreator#postProcessAfterInitialization
/**
	 * 创建代理
	 * Create a proxy with the configured interceptors if the bean is
	 * identified as one to proxy by the subclass.
	 * @see #getAdvicesAndAdvisorsForBean
	 */
@Override
public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
    if (bean != null) {
        /// 生成一个key 如果beanName不为空，则为 &+beanName,否则为 bean的Class
        Object cacheKey = getCacheKey(bean.getClass(), beanName);
        if (this.earlyProxyReferences.remove(cacheKey) != bean) {
            return wrapIfNecessary(bean, beanName, cacheKey);
        }
    }
    return bean;
}

// AbstractAutoProxyCreator#wrapIfNecessary
/**
 * Wrap the given bean if necessary, i.e. if it is eligible for being proxied.
 * @param bean the raw bean instance
 * @param beanName the name of the bean
 * @param cacheKey the cache key for metadata access
 * @return a proxy wrapping the bean, or the raw bean instance as-is
 */
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
    // 如果已经处理过
    if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
        return bean;
    }
    // 无需增强
    if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
        return bean;
    }
    // 给定的bean类是否是一个基础设施类，基础设施类不应该被代理，或者配置了指定的bean不需要代理
    if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
        this.advisedBeans.put(cacheKey, Boolean.FALSE);
        return bean;
    }

    // Create proxy if we have advice.
    *  TransactionInterceptor  切面aspect
    /// 先查找 Advisor 主要包括两种 IntroductionAdvisor 和 PointcutAdvisor,这里会将前面注入的  BeanFactoryTransactionAttributeSourceAdvisor 返回
    Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
    if (specificInterceptors != DO_NOT_PROXY) {
        this.advisedBeans.put(cacheKey, Boolean.TRUE);
        /// 生成代理对象
        Object proxy = createProxy(
                bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
        this.proxyTypes.put(cacheKey, proxy.getClass());
        return proxy;
    }
    /// 标识不能代理
    this.advisedBeans.put(cacheKey, Boolean.FALSE);
    return bean;
}

/**
 * AbstractAdvisorAutoProxyCreator#getAdvicesAndAdvisorsForBean
 */
@Override
@Nullable
protected Object[] getAdvicesAndAdvisorsForBean(
        Class<?> beanClass, String beanName, @Nullable TargetSource targetSource) {

    List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
    if (advisors.isEmpty()) {
        return DO_NOT_PROXY;
    }
    return advisors.toArray();
}

/**
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
 * AbstractAdvisorAutoProxyCreator#
 * 获取所有符合条件的Advisor用于后续自动代理使用，会返回 BeanFactoryTransactionAttributeSourceAdvisor
 * Find all eligible Advisors for auto-proxying this class.
 * @param beanClass the clazz to find advisors for
 * @param beanName the name of the currently proxied bean
 * @return the empty List, not {@code null},
 * if there are no pointcuts or interceptors
 * @see #findCandidateAdvisors
 * @see #sortAdvisors
 * @see #extendAdvisors
 */
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
    List<Advisor> candidateAdvisors = findCandidateAdvisors();
    List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
    extendAdvisors(eligibleAdvisors);
    if (!eligibleAdvisors.isEmpty()) {
        eligibleAdvisors = sortAdvisors(eligibleAdvisors);
    }
    return eligibleAdvisors;
}

/**
 * AbstractAdvisorAutoProxyCreator#findCandidateAdvisors
 * Find all candidate Advisors to use in auto-proxying.
 * @return the List of candidate Advisors
 */
protected List<Advisor> findCandidateAdvisors() {
    Assert.state(this.advisorRetrievalHelper != null, "No BeanFactoryAdvisorRetrievalHelper available");
    return this.advisorRetrievalHelper.findAdvisorBeans();
}

/**
 * AbstractAdvisorAutoProxyCreator#findCandidateAdvisors
 * Search the given candidate Advisors to find all Advisors that
 * can apply to the specified bean.
 * @param candidateAdvisors the candidate Advisors
 * @param beanClass the target's bean class
 * @param beanName the target's bean name
 * @return the List of applicable Advisors
 * @see ProxyCreationContext#getCurrentProxiedBeanName()
 */
protected List<Advisor> findAdvisorsThatCanApply(
        List<Advisor> candidateAdvisors, Class<?> beanClass, String beanName) {

    ProxyCreationContext.setCurrentProxiedBeanName(beanName);
    try {
        return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
    }
    finally {
        ProxyCreationContext.setCurrentProxiedBeanName(null);
    }
}

/**
 * BeanFactoryAdvisorRetrievalHelper#findAdvisorBeans
 * Find all eligible Advisor beans in the current bean factory,
 * ignoring FactoryBeans and excluding beans that are currently in creation.
 * @return the list of {@link org.springframework.aop.Advisor} beans
 * @see #isEligibleBean
 */
public List<Advisor> findAdvisorBeans() {
    // Determine list of advisor bean names, if not cached already.
    String[] advisorNames = this.cachedAdvisorBeanNames;
    if (advisorNames == null) {
        // Do not initialize FactoryBeans here: We need to leave all regular beans
        // uninitialized to let the auto-proxy creator apply to them!
        /// 查找所有的 Advisor Bean
        advisorNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(this.beanFactory, Advisor.class, true, false);
        this.cachedAdvisorBeanNames = advisorNames;
    }
    if (advisorNames.length == 0) {
        return new ArrayList<>();
    }

    List<Advisor> advisors = new ArrayList<>();
    for (String name : advisorNames) {
        if (isEligibleBean(name)) {
            if (this.beanFactory.isCurrentlyInCreation(name)) {
                if (logger.isTraceEnabled()) {
                    logger.trace("Skipping currently created advisor '" + name + "'");
                }
            }
            else {
                try {
                    /// 进行实例化
                    advisors.add(this.beanFactory.getBean(name, Advisor.class));
                }
                catch (BeanCreationException ex) {
                    Throwable rootCause = ex.getMostSpecificCause();
                    if (rootCause instanceof BeanCurrentlyInCreationException) {
                        BeanCreationException bce = (BeanCreationException) rootCause;
                        String bceBeanName = bce.getBeanName();
                        if (bceBeanName != null && this.beanFactory.isCurrentlyInCreation(bceBeanName)) {
                            if (logger.isTraceEnabled()) {
                                logger.trace("Skipping advisor '" + name +
                                        "' with dependency on currently created bean: " + ex.getMessage());
                            }
                            // Ignore: indicates a reference back to the bean we're trying to advise.
                            // We want to find advisors other than the currently created bean itself.
                            continue;
                        }
                    }
                    throw ex;
                }
            }
        }
    }
    return advisors;
}

/**
 * Determine the sublist of the {@code candidateAdvisors} list
 * that is applicable to the given class.
 * @param candidateAdvisors the Advisors to evaluate
 * @param clazz the target class
 * @return sublist of Advisors that can apply to an object of the given class
 * (may be the incoming List as-is)
 */
public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) {
    if (candidateAdvisors.isEmpty()) {
        return candidateAdvisors;
    }
    List<Advisor> eligibleAdvisors = new ArrayList<>();
    for (Advisor candidate : candidateAdvisors) {
        // IntroductionAdvisor 用于增加类方法,创建代理对象后，代理对象实现新的接口方法，进行判断
        if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {
            eligibleAdvisors.add(candidate);
        }
    }
    boolean hasIntroductions = !eligibleAdvisors.isEmpty();
    for (Advisor candidate : candidateAdvisors) {
        if (candidate instanceof IntroductionAdvisor) {
            // already processed
            continue;
        }
        if (canApply(candidate, clazz, hasIntroductions)) {
            eligibleAdvisors.add(candidate);
        }
    }
    return eligibleAdvisors;
}

/**
	 * Can the given pointcut apply at all on the given class?
	 * <p>This is an important test as it can be used to optimize
	 * out a pointcut for a class.
	 * @param pc the static or dynamic pointcut to check
	 * @param targetClass the class to test
	 * @return whether the pointcut can apply on any method
	 */
	public static boolean canApply(Pointcut pc, Class<?> targetClass) {
		return canApply(pc, targetClass, false);
	}

	/**
     * 这里会调用 BeanFactoryTransactionAttributeSourceAdvisor ，判断是否需要进行代理
	 * Can the given pointcut apply at all on the given class?
	 * <p>This is an important test as it can be used to optimize
	 * out a pointcut for a class.
	 * @param pc the static or dynamic pointcut to check  参数为 AnnotationTransactionAttributeSource
	 * @param targetClass the class to test
	 * @param hasIntroductions whether the advisor chain
	 * for this bean includes any introductions
	 * @return whether the pointcut can apply on any method
	 */
	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));
		}
		//获取对应类的所有接口
		classes.addAll(ClassUtils.getAllInterfacesForClassAsSet(targetClass));
		/// 遍历
		for (Class<?> clazz : classes) {
			/// 获取所有方法
			Method[] methods = ReflectionUtils.getAllDeclaredMethods(clazz);
			for (Method method : methods) {
				if (introductionAwareMethodMatcher != null ?
						/// 判断是否符合pointcut 
                        /// 调用 TransactionAttributeSourcePointcut#matches
						introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions) :
						methodMatcher.matches(method, targetClass)) {
					return true;
				}
			}
		}

		return false;
	}

	/**
	 * Can the given advisor apply at all on the given class?
	 * This is an important test as it can be used to optimize
	 * out an advisor for a class.
	 * @param advisor the advisor to check
	 * @param targetClass class we're testing
	 * @return whether the pointcut can apply on any method
	 */
	public static boolean canApply(Advisor advisor, Class<?> targetClass) {
		return canApply(advisor, targetClass, false);
	}

	/**
	 * Can the given advisor apply at all on the given class?
	 * <p>This is an important test as it can be used to optimize out an advisor for a class.
	 * This version also takes into account introductions (for IntroductionAwareMethodMatchers).
	 * @param advisor the advisor to check
	 * @param targetClass class we're testing
	 * @param hasIntroductions whether the advisor chain for this bean includes
	 * any introductions
	 * @return whether the pointcut can apply on any method
	 */
	public static boolean canApply(Advisor advisor, Class<?> targetClass, boolean hasIntroductions) {
        /// 看下是不是IntroductionAdvisor
		if (advisor instanceof IntroductionAdvisor) {
			return ((IntroductionAdvisor) advisor).getClassFilter().matches(targetClass);
		}
		else if (advisor instanceof PointcutAdvisor) { // 查看BeanFactoryTransactionAttributeSourceAdvisor 是否支持
			PointcutAdvisor pca = (PointcutAdvisor) advisor;
            /// BeanFactoryTransactionAttributeSourceAdvisor 的 getPointcut返回的是 TransactionAttributeSourcePointcut, TransactionAttributeSourcePointcut的TransactionAttributeSource在前面注册了
			return canApply(pca.getPointcut(), targetClass, hasIntroductions);
		}
		else {
			// It doesn't have a pointcut so we assume it applies.
			return true;
		}
	}

/**
 * TransactionAttributeSourcePointcut#matches
 */
@Override
public Boolean matches(Method method, Class<?> targetClass) {
    // 自定义标签解析时注入,前面注入的 AnnotationTransactionAttributeSource
    TransactionAttributeSource tas = getTransactionAttributeSource();
    return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
}

/**
 * AnnotationTransactionAttributeSource#getTransactionAttributeSource 调用父类 AbstractFallbackTransactionAttributeSource#getTransactionAttributeSource
 * Determine the transaction attribute for this method invocation.
 * <p>Defaults to the class's transaction attribute if no method attribute is found.
 * @param method the method for the current invocation (never {@code null})
 * @param targetClass the target class for this invocation (may be {@code null})
 * @return a TransactionAttribute for this method, or {@code null} if the method
 * is not transactional
 */
@Override
@Nullable
public TransactionAttribute getTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
    if (method.getDeclaringClass() == Object.class) {
        return null;
    }

    // First, see if we have a cached value.
    Object cacheKey = getCacheKey(method, targetClass);
    TransactionAttribute cached = this.attributeCache.get(cacheKey);
    if (cached != null) {
        // Value will either be canonical value indicating there is no transaction attribute,
        // or an actual transaction attribute.
        if (cached == NULL_TRANSACTION_ATTRIBUTE) {
            return null;
        }
        else {
            return cached;
        }
    }
    else {
        // We need to work it out.
        /// 如果没有缓存，就找一下
        TransactionAttribute txAttr = computeTransactionAttribute(method, targetClass);
        // Put it in the cache.
        if (txAttr == null) {
            this.attributeCache.put(cacheKey, NULL_TRANSACTION_ATTRIBUTE);
        }
        else {
            String methodIdentification = ClassUtils.getQualifiedMethodName(method, targetClass);
            if (txAttr instanceof DefaultTransactionAttribute) {
                DefaultTransactionAttribute dta = (DefaultTransactionAttribute) txAttr;
                dta.setDescriptor(methodIdentification);
                dta.resolveAttributeStrings(this.embeddedValueResolver);
            }
            if (logger.isTraceEnabled()) {
                logger.trace("Adding transactional method '" + methodIdentification + "' with attribute: " + txAttr);
            }
            this.attributeCache.put(cacheKey, txAttr);
        }
        return txAttr;
    }
}

/**
 * AbstractFallbackTransactionAttributeSource#computeTransactionAttribute
 * Same signature as {@link #getTransactionAttribute}, but doesn't cache the result.
 * {@link #getTransactionAttribute} is effectively a caching decorator for this method.
 * <p>As of 4.1.8, this method can be overridden.
 * @since 4.1.8
 * @see #getTransactionAttribute
 */
@Nullable
protected TransactionAttribute computeTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
    // Don't allow non-public methods, as configured. 非public方法，不管
    if (allowPublicMethodsOnly() && !Modifier.isPublic(method.getModifiers())) {
        return null;
    }

    // The method may be on an interface, but we need attributes from the target class.
    // If the target class is null, the method will be unchanged.
    Method specificMethod = AopUtils.getMostSpecificMethod(method, targetClass);

    // First try is the method in the target class.
    /// 看下是不是在目标类中
    TransactionAttribute txAttr = findTransactionAttribute(specificMethod);
    if (txAttr != null) {
        return txAttr;
    }
    // 
    // Second try is the transaction attribute on the target class.
    txAttr = findTransactionAttribute(specificMethod.getDeclaringClass());
    if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {
        return txAttr;
    }

    if (specificMethod != method) {
        // Fallback is to look at the original method.
        txAttr = findTransactionAttribute(method);
        if (txAttr != null) {
            return txAttr;
        }
        // Last fallback is the class of the original method.
        txAttr = findTransactionAttribute(method.getDeclaringClass());
        if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {
            return txAttr;
        }
    }

    return null;
}

/// 查找事务属性，都在 AnnotationTransactionAttributeSource
@Override
	@Nullable
	protected TransactionAttribute findTransactionAttribute(Class<?> clazz) {
		return determineTransactionAttribute(clazz);
	}

	@Override
	@Nullable
	protected TransactionAttribute findTransactionAttribute(Method method) {
		return determineTransactionAttribute(method);
	}

	/**
	 * Determine the transaction attribute for the given method or class.
	 * <p>This implementation delegates to configured
	 * {@link TransactionAnnotationParser TransactionAnnotationParsers}
	 * for parsing known annotations into Spring's metadata attribute class.
	 * Returns {@code null} if it's not transactional.
	 * <p>Can be overridden to support custom annotations that carry transaction metadata.
	 * @param element the annotated method or class
	 * @return the configured transaction attribute, or {@code null} if none was found
	 */
	@Nullable
	protected TransactionAttribute determineTransactionAttribute(AnnotatedElement element) {
        /// annotationParsers是在AnnotationTransactionAttributeSource初始化时加载的
		for (TransactionAnnotationParser parser : this.annotationParsers) {
			TransactionAttribute attr = parser.parseTransactionAnnotation(element);
			if (attr != null) {
				return attr;
			}
		}
		return null;
	}

/**
 *  初始化，加载annotationParsers
	 * Create a custom AnnotationTransactionAttributeSource, supporting
	 * public methods that carry the {@code Transactional} annotation
	 * or the EJB3 {@link javax.ejb.TransactionAttribute} annotation.
	 * @param publicMethodsOnly whether to support public methods that carry
	 * the {@code Transactional} annotation only (typically for use
	 * with proxy-based AOP), or protected/private methods as well
	 * (typically used with AspectJ class weaving)
	 */
	public AnnotationTransactionAttributeSource(boolean publicMethodsOnly) {
		this.publicMethodsOnly = publicMethodsOnly;
		if (jta12Present || ejb3Present) {
			this.annotationParsers = new LinkedHashSet<>(4);
			this.annotationParsers.add(new SpringTransactionAnnotationParser());
			if (jta12Present) {
				this.annotationParsers.add(new JtaTransactionAnnotationParser());
			}
			if (ejb3Present) {
				this.annotationParsers.add(new Ejb3TransactionAnnotationParser());
			}
		}
		else {
			this.annotationParsers = Collections.singleton(new SpringTransactionAnnotationParser());
		}
	}

/*
 * Copyright 2002-2020 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.transaction.annotation;

import java.io.Serializable;
import java.lang.reflect.AnnotatedElement;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import org.springframework.core.annotation.AnnotatedElementUtils;
import org.springframework.core.annotation.AnnotationAttributes;
import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.lang.Nullable;
import org.springframework.transaction.interceptor.NoRollbackRuleAttribute;
import org.springframework.transaction.interceptor.RollbackRuleAttribute;
import org.springframework.transaction.interceptor.RuleBasedTransactionAttribute;
import org.springframework.transaction.interceptor.TransactionAttribute;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

/**
 * Strategy implementation for parsing Spring's {@link Transactional} annotation.
 *
 * @author Juergen Hoeller
 * @author Mark Paluch
 * @since 2.5
 */
@SuppressWarnings("serial")
public class SpringTransactionAnnotationParser implements TransactionAnnotationParser, Serializable {

	@Override
	public boolean isCandidateClass(Class<?> targetClass) {
		return AnnotationUtils.isCandidateClass(targetClass, Transactional.class);
	}

	@Override
	@Nullable
	public TransactionAttribute parseTransactionAnnotation(AnnotatedElement element) {
		AnnotationAttributes attributes = AnnotatedElementUtils.findMergedAnnotationAttributes(
				element, Transactional.class, false, false);
		if (attributes != null) {
			return parseTransactionAnnotation(attributes);
		}
		else {
			return null;
		}
	}

	public TransactionAttribute parseTransactionAnnotation(Transactional ann) {
		return parseTransactionAnnotation(AnnotationUtils.getAnnotationAttributes(ann, false, false));
	}

	protected TransactionAttribute parseTransactionAnnotation(AnnotationAttributes attributes) {
		RuleBasedTransactionAttribute rbta = new RuleBasedTransactionAttribute();

		Propagation propagation = attributes.getEnum("propagation");
		rbta.setPropagationBehavior(propagation.value());
		Isolation isolation = attributes.getEnum("isolation");
		rbta.setIsolationLevel(isolation.value());

		rbta.setTimeout(attributes.getNumber("timeout").intValue());
		String timeoutString = attributes.getString("timeoutString");
		Assert.isTrue(!StringUtils.hasText(timeoutString) || rbta.getTimeout() < 0,
				"Specify 'timeout' or 'timeoutString', not both");
		rbta.setTimeoutString(timeoutString);

		rbta.setReadOnly(attributes.getBoolean("readOnly"));
		rbta.setQualifier(attributes.getString("value"));
		rbta.setLabels(Arrays.asList(attributes.getStringArray("label")));

		List<RollbackRuleAttribute> rollbackRules = new ArrayList<>();
		for (Class<?> rbRule : attributes.getClassArray("rollbackFor")) {
			rollbackRules.add(new RollbackRuleAttribute(rbRule));
		}
		for (String rbRule : attributes.getStringArray("rollbackForClassName")) {
			rollbackRules.add(new RollbackRuleAttribute(rbRule));
		}
		for (Class<?> rbRule : attributes.getClassArray("noRollbackFor")) {
			rollbackRules.add(new NoRollbackRuleAttribute(rbRule));
		}
		for (String rbRule : attributes.getStringArray("noRollbackForClassName")) {
			rollbackRules.add(new NoRollbackRuleAttribute(rbRule));
		}
		rbta.setRollbackRules(rollbackRules);

		return rbta;
	}


	@Override
	public boolean equals(@Nullable Object other) {
		return (other instanceof SpringTransactionAnnotationParser);
	}

	@Override
	public int hashCode() {
		return SpringTransactionAnnotationParser.class.hashCode();
	}

}