Spring提取@Transactional事務注解的源碼解析

聲明：本文是自己在學習spring注解事務處理源代碼時所留下的筆記； 難免有錯誤，敬請讀者諒解！！！

1、事務注解標簽

    <tx:annotation-driven />

2、tx 命名空間解析器 
事務tx命名空間解析器TxNamespaceHandler 
org.springframework.transaction.config.TxNamespaceHandler#init

3、AnnotationDrivenBeanDefinitionParser#parse 解析事務標簽

（1）、以下方法的核心邏輯主要是選擇是否使用 Aspect 方式實現代理，默認方式為 JDK 的動態代理。 
org.springframework.transaction.config.AnnotationDrivenBeanDefinitionParser#parse

public BeanDefinition parse(Element element, ParserContext parserContext) {
    String mode = element.getAttribute("mode");
    if ("aspectj".equals(mode)) {
        // mode="aspectj"
        registerTransactionAspect(element, parserContext);
    }
    else {
        // mode="proxy"   注意 AopAutoProxyConfigurer 為當前內的內部類
        AopAutoProxyConfigurer.configureAutoProxyCreator(element, parserContext);
    }
    return null;
}

（2）、進入如下方法，該方法的核心邏輯通過硬編碼的方式配置 Aop 動態代理的解析器 
AopAutoProxyConfigurer#configureAutoProxyCreator 
通過硬編碼，Spring 為我們定義了如下的 Spring BeanDefinition 對象 
(a)、AnnotationTransactionAttributeSource.class 事務注解屬性解析器BeanDefinition 對象。 
AnnotationTransactionAttributeSource 構造方法會初始化：

public AnnotationTransactionAttributeSource() {
        this(true);
}

public AnnotationTransactionAttributeSource(boolean publicMethodsOnly) {
    this.publicMethodsOnly = publicMethodsOnly;
    this.annotationParsers = new LinkedHashSet<TransactionAnnotationParser>(2);
    this.annotationParsers.add(new SpringTransactionAnnotationParser());// @Transactional 注解解析器
    if (ejb3Present) {
        this.annotationParsers.add(new Ejb3TransactionAnnotationParser());// Ejb 解析器
    }

(b)、TransactionInterceptor.class 事務攔截器BeanDefinition 對象 
(c)、BeanFactoryTransactionAttributeSourceAdvisor.class 事務切面解析器 
(d)、TransactionInterceptor.class 事務攔截器BeanDefinition 對象 
(e)、容易忽略的第一行代碼：AopNamespaceUtils.registerAutoProxyCreatorIfNecessary(parserContext, element); 在這個方法內部 Spring 為我們的注入了：InfrastructureAdvisorAutoProxyCreator.class 

private static class AopAutoProxyConfigurer {

    public static void configureAutoProxyCreator(Element element, ParserContext parserContext) {

        // 非常重要的一行代碼，在這個里面注冊了：InfrastructureAdvisorAutoProxyCreator.class 該類實現了Spring BeanProcessor 的擴展接口
        AopNamespaceUtils.registerAutoProxyCreatorIfNecessary(parserContext, element);

        String txAdvisorBeanName = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME;
        if (!parserContext.getRegistry().containsBeanDefinition(txAdvisorBeanName)) {
            Object eleSource = parserContext.extractSource(element);

            // Create the TransactionAttributeSource definition.
            RootBeanDefinition sourceDef = new RootBeanDefinition(AnnotationTransactionAttributeSource.class);// 事務注解解析器
            sourceDef.setSource(eleSource);
            sourceDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
            String sourceName = parserContext.getReaderContext().registerWithGeneratedName(sourceDef);

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

            // Create the TransactionAttributeSourceAdvisor definition.
            RootBeanDefinition advisorDef = new RootBeanDefinition(BeanFactoryTransactionAttributeSourceAdvisor.class);//事務切面解析器
            advisorDef.setSource(eleSource);
            advisorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
            advisorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
            advisorDef.getPropertyValues().add("adviceBeanName", interceptorName);
            if (element.hasAttribute("order")) {
                advisorDef.getPropertyValues().add("order", element.getAttribute("order"));
            }
            parserContext.getRegistry().registerBeanDefinition(txAdvisorBeanName, advisorDef);

            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);
        }
    }
}

4、Spring Bean 實例化創建代理對象 
（a）、AbstractAutowireCapableBeanFactory#initializeBean(Java.lang.String, java.lang.Object, org.springframework.beans.factory.support.RootBeanDefinition)

（b）、AbstractAutoProxyCreator#postProcessAfterInitialization 

還記得上面我們提到的 InfrastructureAdvisorAutoProxyCreator 的類圖吧，最后我們的 @Transactional 注解的類會執行該類中的 postProcessAfterInitialization 方法

（c）、Bean 的初始化后置處理，通過注釋可以了解到，當前方法處理后會返回一個 bean 的代理對象

/**
 * Create a proxy with the configured interceptors if the bean is
 * identified as one to proxy by the subclass.
 * @see #getAdvicesAndAdvisorsForBean
 */
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    if (bean != null) {
        Object cacheKey = getCacheKey(bean.getClass(), beanName);
        if (!this.earlyProxyReferences.containsKey(cacheKey)) {
            return wrapIfNecessary(bean, beanName, cacheKey);// 創建代理類的核心方法
        }
    }
    return bean;
}

（d）、AbstractAutoProxyCreator#wrapIfNecessary

protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
    if (beanName != null && this.targetSourcedBeans.containsKey(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.   獲取切面   獲取的過程是一個非常復雜的過程
    Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
    if (specificInterceptors != DO_NOT_PROXY) {
        this.advisedBeans.put(cacheKey, Boolean.TRUE);

        // 創建代理對象，默認的情況下會使用 JDK 的動態代理接口創建代理對象
        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;
}

（c）、獲取到的事務切面 

(d)、事務切面獲取邏輯 

(e)、委托 ProxyFactory 創建代理對象

protected Object createProxy(
        Class<?> beanClass, String beanName, Object[] specificInterceptors, TargetSource targetSource) {

    ProxyFactory proxyFactory = new ProxyFactory();
    // Copy our properties (proxyTargetClass etc) inherited from ProxyConfig.
    proxyFactory.copyFrom(this);

    if (!shouldProxyTargetClass(beanClass, beanName)) {
        // Must allow for introductions; can't just set interfaces to
        // the target's interfaces only.
        Class<?>[] targetInterfaces = ClassUtils.getAllInterfacesForClass(beanClass, this.proxyClassLoader);
        for (Class<?> targetInterface : targetInterfaces) {
            proxyFactory.addInterface(targetInterface);
        }
    }

    Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
    for (Advisor advisor : advisors) {
        proxyFactory.addAdvisor(advisor);
    }

    proxyFactory.setTargetSource(targetSource);
    customizeProxyFactory(proxyFactory);

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

    // 最終會使用：JdkDynamicAopProxy  創建事務的Aop 代理對象
    return proxyFactory.getProxy(this.proxyClassLoader);
}

(f)、最終生成代理對象 

5、代理類執行 
JdkDynamicAopProxy#invoke

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    MethodInvocation invocation;
    Object oldProxy = null;
    boolean setProxyContext = false;

    TargetSource targetSource = this.advised.targetSource;
    Class<?> targetClass = null;
    Object target = null;

    try {
        // 如果目標方法沒有實現equals
        if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
            // The target does not implement the equals(Object) method itself.
            return equals(args[0]);
        }
        // 如果目標方法沒有實現hashcode
        if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
            // The target does not implement the hashCode() method itself.
            return hashCode();
        }
        // 根據代理對象的配置來調用服務
        if (!this.advised.opaque && method.getDeclaringClass().isInterface() &&
                method.getDeclaringClass().isAssignableFrom(Advised.class)) {
            // Service invocations on ProxyConfig with the proxy config...
            return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
        }

        Object retVal;

        if (this.advised.exposeProxy) {
            // Make invocation available if necessary.
            oldProxy = AopContext.setCurrentProxy(proxy);
            setProxyContext = true;
        }

        // May be null. Get as late as possible to minimize the time we "own" the target,
        // in case it comes from a pool.
        // 獲取目標對象
        target = targetSource.getTarget();
        if (target != null) {
            targetClass = target.getClass();
        }

        // 獲取定義好的攔截器鏈
        // Get the interception chain for this method.
        List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);

        // Check whether we have any advice. If we don't, we can fallback on direct
        // reflective invocation of the target, and avoid creating a MethodInvocation.
        if (chain.isEmpty()) {
            // We can skip creating a MethodInvocation: just invoke the target directly
            // Note that the final invoker must be an InvokerInterceptor so we know it does
            // nothing but a reflective operation on the target, and no hot swapping or fancy proxying.
            // 沒有攔截鏈則直接調用target方法
            retVal = AopUtils.invokeJoinpointUsingReflection(target, method, args);
        }
        else {
            // We need to create a method invocation...
            //對攔截鏈進行封裝  得到對象ReflectiveMethodInvocation 調用 proceed 方法
            invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
            // Proceed to the joinpoint through the interceptor chain.
            retVal = invocation.proceed();// 方法內部將執行攔截器的切面直到目標方法被執行
        }

        // Massage return value if necessary.
        Class<?> returnType = method.getReturnType();
        if (retVal != null && retVal == target && returnType.isInstance(proxy) &&
                !RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
            // Special case: it returned "this" and the return type of the method
            // is type-compatible. Note that we can't help if the target sets
            // a reference to itself in another returned object.
            retVal = proxy;
        }
        else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) {
            throw new AopInvocationException(
                    "Null return value from advice does not match primitive return type for: " + method);
        }
        return retVal;
    }
    finally {
        if (target != null && !targetSource.isStatic()) {
            // Must have come from TargetSource.
            targetSource.releaseTarget(target);
        }
        if (setProxyContext) {
            // Restore old proxy.
            AopContext.setCurrentProxy(oldProxy);
        }
    }
}

7、代理會執行到： ReflectiveMethodInvocation#proceed 方法

8、最終會執行到：TransactionInterceptor#invoke 方法

9、執行 TransactionAspectSupport 事務方法 
TransactionInterceptor#invoke 方法會調用到父類的 TransactionAspectSupport#invokeWithinTransaction 方法

10、業務方法執行 

11、Spring 事務處理的流程 

（a）、開啟事務 

（b）、事務回滾 

（c）、事務提交 

 

 http://blog.csdn.net/dalinsi/article/details/53203540

 

 

聲明：本編文章是自己在查看spring提取@Transactional注解的源碼過程中隨手記下的筆記，只做了大概流程的記錄，未做詳細分析，如有錯誤還請諒解。

1、事務切面匹配處理類

AopUtils#canApply(Pointcut, Class , boolean) 
方法中會調用到 TransactionAttributeSourcePointcut#matches 方法

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

    Set<Class> classes = new HashSet<Class>(ClassUtils.getAllInterfacesForClassAsSet(targetClass));
    classes.add(targetClass);
    for (Class<?> clazz : classes) {
        Method[] methods = clazz.getMethods();
        for (Method method : methods) {
            //methodMatcher.matches(method, targetClass) 方法會匹配對應的處理類，在Transaction提取的過程中會匹配到：TransactionAttributeSourcePointcut 
            if ((introductionAwareMethodMatcher != null &&
                    introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions)) ||
                    methodMatcher.matches(method, targetClass)) {
                return true;
            }
        }
    }

    return false;
}

2、事務切點匹配

TransactionAttributeSourcePointcut#matches

在閱讀TransactionAttributeSourcePointcut內的源代碼的時候，我們發現該類是一個抽象，但是他確沒有實現的子類！！！那么這個類到底在哪被引用了呢？

abstract class TransactionAttributeSourcePointcut extends StaticMethodMatcherPointcut implements Serializable {

    public boolean matches(Method method, Class targetClass) {

        // 該處調用了 getTransactionAttributeSource() 的抽象方法，但是卻沒有子類實現這個方法，這是怎么一回事呢？
        TransactionAttributeSource tas = getTransactionAttributeSource();
        return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
    }

    @Override
    public boolean equals(Object other) {
        if (this == other) {
            return true;
        }
        if (!(other instanceof TransactionAttributeSourcePointcut)) {
            return false;
        }
        TransactionAttributeSourcePointcut otherPc = (TransactionAttributeSourcePointcut) other;
        return ObjectUtils.nullSafeEquals(getTransactionAttributeSource(), otherPc.getTransactionAttributeSource());
    }

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

    @Override
    public String toString() {
        return getClass().getName() + ": " + getTransactionAttributeSource();
    }


    /**
     * Obtain the underlying TransactionAttributeSource (may be {@code null}).
     * To be implemented by subclasses.
     */
    protected abstract TransactionAttributeSource getTransactionAttributeSource();

}

3、TransactionAttributeSourcePointcut 抽象類的應用

我們懷着上面的疑問全局搜索 TransactionAttributeSourcePointcut 可以在 BeanFactoryTransactionAttributeSourceAdvisor 里面找到如下的代碼：

public class BeanFactoryTransactionAttributeSourceAdvisor extends AbstractBeanFactoryPointcutAdvisor {

    private TransactionAttributeSource transactionAttributeSource;

    // 此處利用了匿名內部類的方式實例化了 TransactionAttributeSourcePointcut 對象，在此我們找到了上面問題的答案。
    private final TransactionAttributeSourcePointcut pointcut = new TransactionAttributeSourcePointcut() {
        @Override
        protected TransactionAttributeSource getTransactionAttributeSource() {
            return transactionAttributeSource;
        }
    };


    /**
     * Set the transaction attribute source which is used to find transaction
     * attributes. This should usually be identical to the source reference
     * set on the transaction interceptor itself.
     * @see TransactionInterceptor#setTransactionAttributeSource
     */
    public void setTransactionAttributeSource(TransactionAttributeSource transactionAttributeSource) {
        this.transactionAttributeSource = transactionAttributeSource;
    }

    /**
     * Set the {@link ClassFilter} to use for this pointcut.
     * Default is {@link ClassFilter#TRUE}.
     */
    public void setClassFilter(ClassFilter classFilter) {
        this.pointcut.setClassFilter(classFilter);
    }

    public Pointcut getPointcut() {
        return this.pointcut;
    }

}

3、TransactionAttributeSource 屬性的 Bean 定義過程

其實，在實例化 BeanFactoryTransactionAttributeSourceAdvisor 時，Spring 已經為我們的 BeanFactoryTransactionAttributeSourceAdvisor 設置了 TransactionAttributeSource 屬性，可以進入 AnnotationDrivenBeanDefinitionParser.AopAutoProxyConfigurer#configureAutoProxyCreator 方法中看源代碼：

private static class AopAutoProxyConfigurer {

    public static void configureAutoProxyCreator(Element element, ParserContext parserContext) {
        AopNamespaceUtils.registerAutoProxyCreatorIfNecessary(parserContext, element);

        String txAdvisorBeanName = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME;
        if (!parserContext.getRegistry().containsBeanDefinition(txAdvisorBeanName)) {
            Object eleSource = parserContext.extractSource(element);

            // 注解事務 transactionAttributeSource Spring 定義的Bean為： AnnotationTransactionAttributeSource 實例
            // Create the TransactionAttributeSource definition.
            RootBeanDefinition sourceDef = new RootBeanDefinition(AnnotationTransactionAttributeSource.class);
            sourceDef.setSource(eleSource);
            sourceDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
            String sourceName = parserContext.getReaderContext().registerWithGeneratedName(sourceDef);

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

            // create BeanFactoryTransactionAttributeSourceAdvisor Bean 的定義
            // Create the TransactionAttributeSourceAdvisor definition.
            RootBeanDefinition advisorDef = new RootBeanDefinition(BeanFactoryTransactionAttributeSourceAdvisor.class);
            advisorDef.setSource(eleSource);
            advisorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
            // 設置 transactionAttributeSource 屬性
            advisorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
            advisorDef.getPropertyValues().add("adviceBeanName", interceptorName);
            if (element.hasAttribute("order")) {
                advisorDef.getPropertyValues().add("order", element.getAttribute("order"));
            }
            parserContext.getRegistry().registerBeanDefinition(txAdvisorBeanName, advisorDef);

            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);
        }
    }
}

4、TransactionAttributeSource#getTransactionAttribute 方法的調用過程

通過以上的分析，我們可以確定 
TransactionAttributeSourcePointcut#getTransactionAttributeSource 返回的是：AnnotationTransactionAttributeSource 實例，AnnotationTransactionAttributeSource繼承自：AbstractFallbackTransactionAttributeSource, 故此TransactionAttributeSourcePointcut#matches 最終會調用到 AbstractFallbackTransactionAttributeSource#getTransactionAttribute 方法

abstract class TransactionAttributeSourcePointcut extends StaticMethodMatcherPointcut implements Serializable {

    public boolean matches(Method method, Class targetClass) {
        TransactionAttributeSource tas = getTransactionAttributeSource();

        // 最終會調用到 AbstractFallbackTransactionAttributeSource#getTransactionAttribute 方法
        return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
    }

    // 省略其他代碼 ……………………
}

再看 AbstractFallbackTransactionAttributeSource#getTransactionAttribute 方法

// 獲取事務屬性
public TransactionAttribute getTransactionAttribute(Method method, Class<?> targetClass) {
    // First, see if we have a cached value.
    Object cacheKey = getCacheKey(method, targetClass);
    Object 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 (TransactionAttribute) cached;
        }
    }
    else {
        // We need to work it out.  根據 method、targetClass 推算事務屬性，TransactionAttribute 
        TransactionAttribute txAtt = computeTransactionAttribute(method, targetClass);
        // Put it in the cache.
        if (txAtt == null) {
            this.attributeCache.put(cacheKey, NULL_TRANSACTION_ATTRIBUTE);
        }
        else {
            if (logger.isDebugEnabled()) {
                logger.debug("Adding transactional method '" + method.getName() + "' with attribute: " + txAtt);
            }
            this.attributeCache.put(cacheKey, txAtt);
        }
        return txAtt;
    }
}

5、事務屬性的推算過程：

// 推算事務屬性，TransactionAttribute 
private TransactionAttribute computeTransactionAttribute(Method method, Class<?> targetClass) {
    // Don't allow no-public methods as required.
    if (allowPublicMethodsOnly() && !Modifier.isPublic(method.getModifiers())) {
        return null;
    }

    // Ignore CGLIB subclasses - introspect the actual user class.
    Class<?> userClass = ClassUtils.getUserClass(targetClass);
    // 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 = ClassUtils.getMostSpecificMethod(method, userClass);
    // If we are dealing with method with generic parameters, find the original method.
    specificMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);

    // 通過上面的分析，findTransactionAttribute 該方法最終會調用到：AnnotationTransactionAttributeSource#findTransactionAttribute(java.lang.Class<?>) 

    // First try is the method in the target class. 方式1： 從目標類的方法上找 Transaction注解
    TransactionAttribute txAtt = findTransactionAttribute(specificMethod);
    if (txAtt != null) {
        return txAtt;
    }

    // Second try is the transaction attribute on the target class.  方式2： 從目標類上找 Transaction注解
    txAtt = findTransactionAttribute(specificMethod.getDeclaringClass());
    if (txAtt != null) {
        return txAtt;
    }

    if (specificMethod != method) {// 以上兩種方式如果還沒有找到 TransactionAttribute 屬性，那就要從目標類的接口開始找
        // Fallback is to look at the original method.  方式3：接口的方法上找 Transaction注解
        txAtt = findTransactionAttribute(method);
        if (txAtt != null) {
            return txAtt;
        }
        // Last fallback is the class of the original method.  方式4：接口的類上找 Transaction注解
        return findTransactionAttribute(method.getDeclaringClass());
    }
    return null;
}

６、事務注解屬性的解析

AnnotationTransactionAttributeSource#findTransactionAttribute(Java.lang.Class

7、獲取事務注解

public class SpringTransactionAnnotationParser implements TransactionAnnotationParser, Serializable {

    public TransactionAttribute parseTransactionAnnotation(AnnotatedElement ae) {
        //獲取 Transactional 注解
        Transactional ann = AnnotationUtils.getAnnotation(ae, Transactional.class);
        if (ann != null) {
            //從 @Transactional 注解上獲取事務屬性值，並包裝成 TransactionAttribute 返回
            return parseTransactionAnnotation(ann);
        }
        else {
            return null;
        }
    }

    public TransactionAttribute parseTransactionAnnotation(Transactional ann) {
        RuleBasedTransactionAttribute rbta = new RuleBasedTransactionAttribute();
        rbta.setPropagationBehavior(ann.propagation().value());
        rbta.setIsolationLevel(ann.isolation().value());
        rbta.setTimeout(ann.timeout());
        rbta.setReadOnly(ann.readOnly());
        rbta.setQualifier(ann.value());
        ArrayList<RollbackRuleAttribute> rollBackRules = new ArrayList<RollbackRuleAttribute>();
        Class[] rbf = ann.rollbackFor();
        for (Class rbRule : rbf) {
            RollbackRuleAttribute rule = new RollbackRuleAttribute(rbRule);
            rollBackRules.add(rule);
        }
        String[] rbfc = ann.rollbackForClassName();
        for (String rbRule : rbfc) {
            RollbackRuleAttribute rule = new RollbackRuleAttribute(rbRule);
            rollBackRules.add(rule);
        }
        Class[] nrbf = ann.noRollbackFor();
        for (Class rbRule : nrbf) {
            NoRollbackRuleAttribute rule = new NoRollbackRuleAttribute(rbRule);
            rollBackRules.add(rule);
        }
        String[] nrbfc = ann.noRollbackForClassName();
        for (String rbRule : nrbfc) {
            NoRollbackRuleAttribute rule = new NoRollbackRuleAttribute(rbRule);
            rollBackRules.add(rule);
        }
        rbta.getRollbackRules().addAll(rollBackRules);
        return rbta;
    }

    @Override
    public boolean equals(Object other) {
        return (this == other || other instanceof SpringTransactionAnnotationParser);
    }

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

}


http://blog.csdn.net/dalinsi/article/details/53215041