Spring 事务源码

　　Spring 的源码一般从@EnableXX 开始看，然后会导入@Enable 一般通过@Import 导入一些相关的配置类。

0. 前沿

ACID Atomicity Consistency Isolation Durabiliry

- 原子性事务要么全做要么不做
- 一致性事务前后的状态是一致的，不会造成数据不一致的状态
- 隔离性多个事务直接互相不影响
- 永久性一个事务commit 之后对数据的影响是永久性的

脏读：事务A读取到事务B未提交的数据

不可重复度：事务A两次读取同一条数据内容不一致，也就是读到了其他事务修改掉的数据

幻读/虚读：两次读取到的数据量不一致

关于隔离级别与事务问题对应关系如下：

　　对于Mysql 来说，RR 隔离级别也不存在虚读的问题，也就是Mysql 事务读取不到其他事务新增加的数据。采用多版本并发控制（MVCC）机制解决幻读问题。

测试：

表结构：

CREATE TABLE `account` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `accountName` varchar(20) DEFAULT NULL,
  `user` varchar(20) DEFAULT NULL,
  `money` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8

1. 脏读问题测试：

(1) session1:

SET tx_isolation = 'read-uncommitted';

BEGIN;

INSERT INTO account(accountName, USER, money) VALUES('zs', 'zs', 100)

ROLLBACK;

COMMIT;

(2) session2

SET tx_isolation = 'read-uncommitted';

SELECT * FROM account;

结果： session2 会读到未提交的数据

2. 不可重复读：两次读到的数据内容不一致

插入一条数据：

(1) session1 执行如下：

SET tx_isolation = 'read-committed';

BEGIN;

select * from account;

# 做其他操作
select * from account;

COMMIT;

(2) session2 如下：

SET tx_isolation = 'read-committed';

BEGIN;

update account set money = money + 1;

COMMIT;

测试：

session1 先执行第一次select，结果如下：

session2 进行update：
session1 第二次进行select，结果如下： (一次事务多次读取数据内容不一致)

3. 幻读：同一个事务两次读到的数据量不一致

(1) session1

SET tx_isolation = 'repeatable-read';

BEGIN;

select * from account;

# 另外一条事务插入数据

select * from account;

insert into account(accountName, user, money) values('zs', 'zs', 100)

select * from account;

update account set money = money + 1 where user = 'zs';

select * from account;

update account set money = money + 1 where user = 'wangwu';

select * from account;

COMMIT;

(2) session2:

SET tx_isolation = 'repeatable-read';

BEGIN;

insert into account(accountName, user, money) values('wangwu', 'wangwu', 100);

commit;

测试：

(1) 确保数据库只有一条数据: 新开事务插入一条数据

truncate table account; 
insert into account(accountName, user, money) values('lisi', 'lisi', 100);
select * from account;

(2) 执行session1 第一次查询语句之前的开启事务以及查询语句：

(3) 执行session2 的insert 操作，并且提交

(4) 新事务查询

(5) 执行session1 第二次查询语句：

(6) 执行session1 的insert 操作

(7) 再次执行session1 的第三次查询

(8) 执行session1 的修改操作

(9) 再次执行session1 的查询操作

(10) 执行session1 的第二次修改

(11) 最后再次查询，发现数据多出来一条

可以看出，update 是采用的当前读，虽然当前事务没有查到相关数据，但是update 也会成功，并且update 之后会将update 的数据加入当前事务。

1. 配置类解读

事务的入口： org.springframework.transaction.annotation.EnableTransactionManagement

package org.springframework.transaction.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.context.annotation.AdviceMode;
import org.springframework.context.annotation.Import;
import org.springframework.core.Ordered;

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(TransactionManagementConfigurationSelector.class)
public @interface EnableTransactionManagement {
    boolean proxyTargetClass() default false;

    AdviceMode mode() default AdviceMode.PROXY;


    int order() default Ordered.LOWEST_PRECEDENCE;

}

通过@Import 引入了TransactionManagementConfigurationSelector

package org.springframework.transaction.annotation;

import org.springframework.context.annotation.AdviceMode;
import org.springframework.context.annotation.AdviceModeImportSelector;
import org.springframework.context.annotation.AutoProxyRegistrar;
import org.springframework.transaction.config.TransactionManagementConfigUtils;
import org.springframework.util.ClassUtils;


public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> {
    @Override
    protected String[] selectImports(AdviceMode adviceMode) {
        switch (adviceMode) {
            case PROXY:
                return new String[] {AutoProxyRegistrar.class.getName(),
                        ProxyTransactionManagementConfiguration.class.getName()};
            case ASPECTJ:
                return new String[] {determineTransactionAspectClass()};
            default:
                return null;
        }
    }

    private String determineTransactionAspectClass() {
        return (ClassUtils.isPresent("javax.transaction.Transactional", getClass().getClassLoader()) ?
                TransactionManagementConfigUtils.JTA_TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME :
                TransactionManagementConfigUtils.TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME);
    }

}

这里会注入ProxyTransactionManagementConfiguration，自动配置类：org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration，这个类注入了几个重要的事务相关bean

package org.springframework.transaction.annotation;

import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Role;
import org.springframework.transaction.config.TransactionManagementConfigUtils;
import org.springframework.transaction.interceptor.BeanFactoryTransactionAttributeSourceAdvisor;
import org.springframework.transaction.interceptor.TransactionAttributeSource;
import org.springframework.transaction.interceptor.TransactionInterceptor;

@Configuration(proxyBeanMethods = false)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public class ProxyTransactionManagementConfiguration extends AbstractTransactionManagementConfiguration {

    @Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)
    @Role(BeanDefinition.ROLE_INFRASTRUCTURE)
    public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor(
            TransactionAttributeSource transactionAttributeSource, TransactionInterceptor transactionInterceptor) {

        BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();
        advisor.setTransactionAttributeSource(transactionAttributeSource);
        advisor.setAdvice(transactionInterceptor);
        if (this.enableTx != null) {
            advisor.setOrder(this.enableTx.<Integer>getNumber("order"));
        }
        return advisor;
    }

    @Bean
    @Role(BeanDefinition.ROLE_INFRASTRUCTURE)
    public TransactionAttributeSource transactionAttributeSource() {
        return new AnnotationTransactionAttributeSource();
    }

    @Bean
    @Role(BeanDefinition.ROLE_INFRASTRUCTURE)
    public TransactionInterceptor transactionInterceptor(TransactionAttributeSource transactionAttributeSource) {
        TransactionInterceptor interceptor = new TransactionInterceptor();
        interceptor.setTransactionAttributeSource(transactionAttributeSource);
        if (this.txManager != null) {
            interceptor.setTransactionManager(this.txManager);
        }
        return interceptor;
    }

}

(1) org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration 事务自动配置的相关类

(2) org.springframework.transaction.interceptor.BeanFactoryTransactionAttributeSourceAdvisor 可以理解为切面Aspect的角色(内部维护Point与Advisor)

(3) org.springframework.transaction.interceptor.TransactionAttributeSource 用于获取TransactionAttribute 事务属性，也就是读取@Transactional 注解上的相关属性

(4) org.springframework.transaction.interceptor.TransactionAttributeSourcePointcut#TransactionAttributeSourcePointcut (是否需要进行事务的控制是在这个类进行判断的)

(5) org.springframework.transaction.interceptor.TransactionInterceptor 事务拦截器。 (对事务的处理是在这个类)

2. 分析过程

事务的拦截器入口： org.springframework.transaction.interceptor.BeanFactoryTransactionAttributeSourceAdvisor，源码如下：

package org.springframework.transaction.interceptor;

import org.springframework.aop.ClassFilter;
import org.springframework.aop.Pointcut;
import org.springframework.aop.support.AbstractBeanFactoryPointcutAdvisor;
import org.springframework.lang.Nullable;
@SuppressWarnings("serial")
public class BeanFactoryTransactionAttributeSourceAdvisor extends AbstractBeanFactoryPointcutAdvisor {

    @Nullable
    private TransactionAttributeSource transactionAttributeSource;

    private final TransactionAttributeSourcePointcut pointcut = new TransactionAttributeSourcePointcut() {
        @Override
        @Nullable
        protected TransactionAttributeSource getTransactionAttributeSource() {
            return transactionAttributeSource;
        }
    };

    public void setTransactionAttributeSource(TransactionAttributeSource transactionAttributeSource) {
        this.transactionAttributeSource = transactionAttributeSource;
    }

    public void setClassFilter(ClassFilter classFilter) {
        this.pointcut.setClassFilter(classFilter);
    }

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

}

TransactionAttributeSource：上面配置类设置的 org.springframework.transaction.annotation.AnnotationTransactionAttributeSource, 用于获取TransactionAttribute 事务属性，也就是读取@Transactional 注解上的相关属性

pointcut 切入点: org.springframework.transaction.interceptor.TransactionAttributeSourcePointcut#TransactionAttributeSourcePointcut (是否需要进行事务的控制是在这个类进行判断的)

advice 通知: org.springframework.transaction.interceptor.TransactionInterceptor 事务拦截器。 (对事务的处理是在这个类)

3. 事务属性TransactionAttribute解析构造过程

0. 事务测试类：

package com.xm.ggn.test;

import com.xm.ggn.bean.common.Message;
import com.xm.ggn.mapper.common.MessageMapper;
import org.springframework.aop.framework.AopContext;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Service;

import javax.transaction.Transactional;
import java.sql.SQLException;

@Service
// Primary可以理解为默认优先选择,不可以同时设置多个,内部实质是设置BeanDefinition的primary属性。
@Primary
//@Transactional
public class MessageService2Impl implements MessageService2 {

    @Autowired
    private MessageMapper messageMapper;

    @Override
    @Transactional
    public void tx1() {
        // 调用tx3方法会回滚，因为这里有事务直接，会走代理，且tx3方法会加入本事务
        tx3();
    }

    @Override
    public void tx2() {
        // 调用tx3方法不会回滚，因为这里没有事务。即使tx3有事务也不会走代理，因为通过内部方法调用不会走代理。解决办法查看tx4 方法
        tx3();
    }

    @Override
    @Transactional
    public void tx3() {
        Message message = new Message();
        message.setTitle("tx3");
        messageMapper.insert(message);

        int i = 1 / 0;
    }

    //  这样进行方法内部调用AOP会生效，主启动类加@EnableAspectJAutoProxy(proxyTargetClass = true, exposeProxy = true) 注解
    @Override
    public void tx4() {
        MessageService2 messageService = (MessageService2) AopContext.currentProxy();
        // 这样调用tx3会进行回滚，走的是代理类的方法
        messageService.tx3();
    }

    @Override
    @Transactional(rollbackOn = Exception.class)
    public void tx5() throws SQLException {
        Message message = new Message();
        message.setTitle("tx3");
        messageMapper.insert(message);

        throw new SQLException("xxx");
    }
}

1. AOP程序入口 org.springframework.aop.framework.CglibAopProxy.DynamicAdvisedInterceptor#intercept

        @Nullable
        public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
            Object oldProxy = null;
            boolean setProxyContext = false;
            Object target = null;
            TargetSource targetSource = this.advised.getTargetSource();

            Object var16;
            try {
                if (this.advised.exposeProxy) {
                    oldProxy = AopContext.setCurrentProxy(proxy);
                    setProxyContext = true;
                }

                target = targetSource.getTarget();
                Class<?> targetClass = target != null ? target.getClass() : null;
                List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
                Object retVal;
                if (chain.isEmpty() && Modifier.isPublic(method.getModifiers())) {
                    Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
                    retVal = methodProxy.invoke(target, argsToUse);
                } else {
                    retVal = (new CglibAopProxy.CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy)).proceed();
                }

                retVal = CglibAopProxy.processReturnType(proxy, target, method, retVal);
                var16 = retVal;
            } finally {
                if (target != null && !targetSource.isStatic()) {
                    targetSource.releaseTarget(target);
                }

                if (setProxyContext) {
                    AopContext.setCurrentProxy(oldProxy);
                }

            }

            return var16;
        }

这里的核心是获取一个AOP调用链条， List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass); 所以是否需要事务控制只需要判断该chain 是否包含对应的Inteceptor。

(1) 针对tx1() 方法进行测试：获取到的chain 如下 = 可以看到有事务拦截器。则会用AOP进行事务处理

(2) 针对tx2() 方法进行测试：获取到的chain 如下 = 可以看到没有事务相关的拦截器，则事务不会生效

2. 获取方法对应的AOP链分析

org.springframework.aop.framework.AdvisedSupport#getInterceptorsAndDynamicInterceptionAdvice 方法根据方法获取对应的AOP处理器链

    public List<Object> getInterceptorsAndDynamicInterceptionAdvice(Method method, @Nullable Class<?> targetClass) {
        AdvisedSupport.MethodCacheKey cacheKey = new AdvisedSupport.MethodCacheKey(method);
        List<Object> cached = (List)this.methodCache.get(cacheKey);
        if (cached == null) {
            cached = this.advisorChainFactory.getInterceptorsAndDynamicInterceptionAdvice(this, method, targetClass);
            this.methodCache.put(cacheKey, cached);
        }

        return cached;
    }

　　可以看到会从缓存中拿，如果缓存中拿不到就会调用方法org.springframework.aop.framework.DefaultAdvisorChainFactory#getInterceptorsAndDynamicInterceptionAdvice 获取并且放到缓存map。所以需要从org.springframework.aop.framework.DefaultAdvisorChainFactory#getInterceptorsAndDynamicInterceptionAdvice 方法获取需要加载的AOP处理器链。

1. 分析 tx1() 方法获取AOP处理器链的过程：

最终获取的方法会打到： org.springframework.aop.framework.DefaultAdvisorChainFactory#getInterceptorsAndDynamicInterceptionAdvice

    public List<Object> getInterceptorsAndDynamicInterceptionAdvice(Advised config, Method method, @Nullable Class<?> targetClass) {
        AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();
        Advisor[] advisors = config.getAdvisors();
        List<Object> interceptorList = new ArrayList(advisors.length);
        Class<?> actualClass = targetClass != null ? targetClass : method.getDeclaringClass();
        Boolean hasIntroductions = null;
        Advisor[] var9 = advisors;
        int var10 = advisors.length;

        for(int var11 = 0; var11 < var10; ++var11) {
            Advisor advisor = var9[var11];
            if (advisor instanceof PointcutAdvisor) {
                PointcutAdvisor pointcutAdvisor = (PointcutAdvisor)advisor;
                if (config.isPreFiltered() || pointcutAdvisor.getPointcut().getClassFilter().matches(actualClass)) {
                    MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher();
                    boolean match;
                    if (mm instanceof IntroductionAwareMethodMatcher) {
                        if (hasIntroductions == null) {
                            hasIntroductions = hasMatchingIntroductions(advisors, actualClass);
                        }

                        match = ((IntroductionAwareMethodMatcher)mm).matches(method, actualClass, hasIntroductions);
                    } else {
                        match = mm.matches(method, actualClass);
                    }

                    if (match) {
                        MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
                        if (mm.isRuntime()) {
                            MethodInterceptor[] var17 = interceptors;
                            int var18 = interceptors.length;

                            for(int var19 = 0; var19 < var18; ++var19) {
                                MethodInterceptor interceptor = var17[var19];
                                interceptorList.add(new InterceptorAndDynamicMethodMatcher(interceptor, mm));
                            }
                        } else {
                            interceptorList.addAll(Arrays.asList(interceptors));
                        }
                    }
                }
            } else if (advisor instanceof IntroductionAdvisor) {
                IntroductionAdvisor ia = (IntroductionAdvisor)advisor;
                if (config.isPreFiltered() || ia.getClassFilter().matches(actualClass)) {
                    Interceptor[] interceptors = registry.getInterceptors(advisor);
                    interceptorList.addAll(Arrays.asList(interceptors));
                }
            } else {
                Interceptor[] interceptors = registry.getInterceptors(advisor);
                interceptorList.addAll(Arrays.asList(interceptors));
            }
        }

        return interceptorList;
    }

(1) config.getAdvisors(); 获取到所有的通知，获取到的通知的数组如下：

(2) 遍历上面获取的通知，然后根据方法转交给MethodMatcher判断是否需要进行AOP处理器链调用。比如对于下标为2的Advisor获取到的MethodMatcher 是：

(3) 调用org.springframework.transaction.interceptor.TransactionAttributeSourcePointcut#matches 方法判断是否需要添加此AOP

    @Override
    public boolean matches(Method method, Class<?> targetClass) {
        TransactionAttributeSource tas = getTransactionAttributeSource();
        return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
    }

-1》这里首先获取TransactionAttributeSource，这里获取到的就是AnnotationTransactionAttributeSource

-2》调用方法org.springframework.transaction.interceptor.AbstractFallbackTransactionAttributeSource#getTransactionAttribute 获取方法对应的事务属性

    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.
            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) txAttr).setDescriptor(methodIdentification);
                }
                if (logger.isTraceEnabled()) {
                    logger.trace("Adding transactional method '" + methodIdentification + "' with attribute: " + txAttr);
                }
                this.attributeCache.put(cacheKey, txAttr);
            }
            return txAttr;
        }
    }

这里先构造一个cacheKey， org.springframework.transaction.interceptor.AbstractFallbackTransactionAttributeSource#getCacheKey

    protected Object getCacheKey(Method method, @Nullable Class<?> targetClass) {
        return new MethodClassKey(method, targetClass);
    }

对于上面的方法tx1() 获取到的cacheKey 如下：

用上面获取的cacheKey 作为key 从缓存map attributeCache 中拿取，org.springframework.transaction.interceptor.AbstractFallbackTransactionAttributeSource#attributeCache如下：

    private final Map<Object, TransactionAttribute> attributeCache = new ConcurrentHashMap<>(1024);

对于上面tx1() 方法获取到的TransactionAttribute 属性如下：可以看到默认的传播行为是PROPAGATION_REQUIRED，默认的事务隔离级别是采用数据库的隔离级别

　　然后将获取到的TransactionAttribute 属性返回去。也就是获取到此对象就需要事务AOP，否则不需要。

2. org.springframework.transaction.interceptor.AbstractFallbackTransactionAttributeSource#attributeCache 存数据过程

　　这个缓存存数据的过程也就是解析方法对应的事务属性TransactionAttribute 的过程。

看是什么时候存储的，只需要查看什么时候put的，发现是在方法：org.springframework.transaction.interceptor.AbstractFallbackTransactionAttributeSource#getTransactionAttribute，断点查看调用链如下：

通过上面了解到，判断一个方法是否需要事务AOP处理是从org.springframework.transaction.interceptor.AbstractFallbackTransactionAttributeSource#attributeCache 判断的，接下来研究这个map 是什么时候存入数据的。

(1) SpringIoC 对象创建过程中会调用org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#wrapIfNecessary，

方法内部调用org.springframework.aop.framework.autoproxy.AbstractAdvisorAutoProxyCreator#getAdvicesAndAdvisorsForBean 获取Advisor[],

最终会调用到方法 org.springframework.transaction.interceptor.TransactionAttributeSourcePointcut#matches，也就是上面判断是否需要进行事务AOP，然后调用到方法org.springframework.transaction.interceptor.AbstractFallbackTransactionAttributeSource#getTransactionAttribute

    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.
            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) txAttr).setDescriptor(methodIdentification);
                }
                if (logger.isTraceEnabled()) {
                    logger.trace("Adding transactional method '" + methodIdentification + "' with attribute: " + txAttr);
                }
                this.attributeCache.put(cacheKey, txAttr);
            }
            return txAttr;
        }
    }

　　根据方法和类构造一个 cacheKey 对象(实际类型是org.springframework.core.MethodClassKey，也就是将方法和class 封装成一个对象作为key)，然后刚进来获取到的cached 为null，所以会走下面的第一次计算并且获取TransactionAttribute 对象。

(2) 接下来走 org.springframework.transaction.interceptor.AbstractFallbackTransactionAttributeSource#computeTransactionAttribute：

    protected TransactionAttribute computeTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
        // Don't allow no-public methods as required.
        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.
        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;
    }

　　这里的逻辑是：先从方法上获取，然后从类上获取。也就是先以方法的为准，然后以类上的为准。

1》首先从方法上获取注解：org.springframework.transaction.annotation.AnnotationTransactionAttributeSource#findTransactionAttribute(java.lang.reflect.Method)

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

转交给方法：org.springframework.transaction.annotation.AnnotationTransactionAttributeSource#determineTransactionAttribute

    protected TransactionAttribute determineTransactionAttribute(AnnotatedElement element) {
        for (TransactionAnnotationParser parser : this.annotationParsers) {
            TransactionAttribute attr = parser.parseTransactionAnnotation(element);
            if (attr != null) {
                return attr;
            }
        }
        return null;
    }

这里获取Set<TransactionAnnotationParser> annotationParsers ，然后遍历获取TransactionAttribute， annotationParsers 如下：

可以看到这里有两个解析器。第一个是解析Spring 包下面的Transactional注解的解析器，第二个是解析javax包下面的Transactional 注解的解析器。也就是两个注解都可以，对应两个不同的解析器。

org.springframework.transaction.annotation.SpringTransactionAnnotationParser#parseTransactionAnnotation(java.lang.reflect.AnnotatedElement) 解析个过程如下：

首先获取Spring包下面的注解：

    @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;
        }
    }

获取到之后调用方法parseTransactionAnnotation 解析并且封装事务属性，获取注解的方法委托给Spring 的工具类 org.springframework.core.annotation.AnnotatedElementUtils#findMergedAnnotationAttributes(java.lang.reflect.AnnotatedElement, java.lang.Class<? extends java.lang.annotation.Annotation>, boolean, boolean)，封装TransactionAttribute 对象的过程如下：

    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());
        rbta.setReadOnly(attributes.getBoolean("readOnly"));
        rbta.setQualifier(attributes.getString("value"));

        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;
    }

org.springframework.transaction.annotation.JtaTransactionAnnotationParser事务解析器中获取到javax.transaction.Transactional 注解封装事务属性过程如下：

org.springframework.transaction.annotation.JtaTransactionAnnotationParser#parseTransactionAnnotation(java.lang.reflect.AnnotatedElement) 方法如下：

    public TransactionAttribute parseTransactionAnnotation(AnnotatedElement element) {
        AnnotationAttributes attributes = AnnotatedElementUtils.getMergedAnnotationAttributes(
                element, javax.transaction.Transactional.class);
        if (attributes != null) {
            return parseTransactionAnnotation(attributes);
        }
        else {
            return null;
        }
    }

　　首先获取方法Transactional 注解的属性并封装到AnnotationAttributes，然后调用：调用方法org.springframework.transaction.annotation.JtaTransactionAnnotationParser#parseTransactionAnnotation(org.springframework.core.annotation.AnnotationAttributes) 组装成 TransactionAttribute

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

        // 获取事务的 传播特性
        rbta.setPropagationBehaviorName(
                RuleBasedTransactionAttribute.PREFIX_PROPAGATION + attributes.getEnum("value").toString());

        // 建立rolebackOn 和 dontRollbackOn 特性
        List<RollbackRuleAttribute> rollbackRules = new ArrayList<>();
        for (Class<?> rbRule : attributes.getClassArray("rollbackOn")) {
            rollbackRules.add(new RollbackRuleAttribute(rbRule));
        }
        for (Class<?> rbRule : attributes.getClassArray("dontRollbackOn")) {
            rollbackRules.add(new NoRollbackRuleAttribute(rbRule));
        }
        rbta.setRollbackRules(rollbackRules);

        return rbta;
    }

　　将获取到的TransactionAttribute 返回给方法org.springframework.transaction.interceptor.AbstractFallbackTransactionAttributeSource#getTransactionAttribute。然后缓存到本地的attributeCache 属性中。

4. 事务处理过程分析

　　上面研究了事务属性的解析过程，大致过程是先解析方法上是否有事务属性，也就是是否有@Transactional 注解(包含javax.transaction包和Spring包的，对应两种解析器)；如果方法没找到就从类上找，类上找的时候也会从类继承的接口上找，所以事务注解具有了继承性。找到之后存到org.springframework.transaction.interceptor.AbstractFallbackTransactionAttributeSource#attributeCache缓存Map中；如果没找到也存一个默认的空对象进去，Map的key是类和方法组成的一个对象。此缓存Map 用于之后判断某个方法在AOP调用链获取过程中判断是否需要进行事务通知的处理。接下来研究事务通知的处理过程。

1. 事务通知入口：

org.springframework.transaction.interceptor.TransactionInterceptor#invoke (该方法继承自org.aopalliance.intercept.MethodInterceptor#invoke)

    @Override
    @Nullable
    public Object invoke(MethodInvocation invocation) throws Throwable {
        // Work out the target class: may be {@code null}.
        // The TransactionAttributeSource should be passed the target class
        // as well as the method, which may be from an interface.
        Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);

        // Adapt to TransactionAspectSupport's invokeWithinTransaction...
        return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);
    }

2. 然后请求转交给父类org.springframework.transaction.interceptor.TransactionAspectSupport#invokeWithinTransaction

    @Nullable
    protected Object invokeWithinTransaction(Method method, @Nullable Class<?> targetClass,
            final InvocationCallback invocation) throws Throwable {

        // If the transaction attribute is null, the method is non-transactional.
        TransactionAttributeSource tas = getTransactionAttributeSource();
        final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
        final TransactionManager tm = determineTransactionManager(txAttr);

        if (this.reactiveAdapterRegistry != null && tm instanceof ReactiveTransactionManager) {
            ReactiveTransactionSupport txSupport = this.transactionSupportCache.computeIfAbsent(method, key -> {
                if (KotlinDetector.isKotlinType(method.getDeclaringClass()) && KotlinDelegate.isSuspend(method)) {
                    throw new TransactionUsageException(
                            "Unsupported annotated transaction on suspending function detected: " + method +
                            ". Use TransactionalOperator.transactional extensions instead.");
                }
                ReactiveAdapter adapter = this.reactiveAdapterRegistry.getAdapter(method.getReturnType());
                if (adapter == null) {
                    throw new IllegalStateException("Cannot apply reactive transaction to non-reactive return type: " +
                            method.getReturnType());
                }
                return new ReactiveTransactionSupport(adapter);
            });
            return txSupport.invokeWithinTransaction(
                    method, targetClass, invocation, txAttr, (ReactiveTransactionManager) tm);
        }

        PlatformTransactionManager ptm = asPlatformTransactionManager(tm);
        final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);

        if (txAttr == null || !(ptm instanceof CallbackPreferringPlatformTransactionManager)) {
            // Standard transaction demarcation with getTransaction and commit/rollback calls.
            TransactionInfo txInfo = createTransactionIfNecessary(ptm, txAttr, joinpointIdentification);

            Object retVal;
            try {
                // This is an around advice: Invoke the next interceptor in the chain.
                // This will normally result in a target object being invoked.
                retVal = invocation.proceedWithInvocation();
            }
            catch (Throwable ex) {
                // target invocation exception
                completeTransactionAfterThrowing(txInfo, ex);
                throw ex;
            }
            finally {
                cleanupTransactionInfo(txInfo);
            }

            if (vavrPresent && VavrDelegate.isVavrTry(retVal)) {
                // Set rollback-only in case of Vavr failure matching our rollback rules...
                TransactionStatus status = txInfo.getTransactionStatus();
                if (status != null && txAttr != null) {
                    retVal = VavrDelegate.evaluateTryFailure(retVal, txAttr, status);
                }
            }

            commitTransactionAfterReturning(txInfo);
            return retVal;
        }

        else {
            final ThrowableHolder throwableHolder = new ThrowableHolder();

            // It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.
            try {
                Object result = ((CallbackPreferringPlatformTransactionManager) ptm).execute(txAttr, status -> {
                    TransactionInfo txInfo = prepareTransactionInfo(ptm, txAttr, joinpointIdentification, status);
                    try {
                        Object retVal = invocation.proceedWithInvocation();
                        if (vavrPresent && VavrDelegate.isVavrTry(retVal)) {
                            // Set rollback-only in case of Vavr failure matching our rollback rules...
                            retVal = VavrDelegate.evaluateTryFailure(retVal, txAttr, status);
                        }
                        return retVal;
                    }
                    catch (Throwable ex) {
                        if (txAttr.rollbackOn(ex)) {
                            // A RuntimeException: will lead to a rollback.
                            if (ex instanceof RuntimeException) {
                                throw (RuntimeException) ex;
                            }
                            else {
                                throw new ThrowableHolderException(ex);
                            }
                        }
                        else {
                            // A normal return value: will lead to a commit.
                            throwableHolder.throwable = ex;
                            return null;
                        }
                    }
                    finally {
                        cleanupTransactionInfo(txInfo);
                    }
                });

                // Check result state: It might indicate a Throwable to rethrow.
                if (throwableHolder.throwable != null) {
                    throw throwableHolder.throwable;
                }
                return result;
            }
            catch (ThrowableHolderException ex) {
                throw ex.getCause();
            }
            catch (TransactionSystemException ex2) {
                if (throwableHolder.throwable != null) {
                    logger.error("Application exception overridden by commit exception", throwableHolder.throwable);
                    ex2.initApplicationException(throwableHolder.throwable);
                }
                throw ex2;
            }
            catch (Throwable ex2) {
                if (throwableHolder.throwable != null) {
                    logger.error("Application exception overridden by commit exception", throwableHolder.throwable);
                }
                throw ex2;
            }
        }
    }

所以事务的核心逻辑代码是在这个方法内部，下面着重分析这个方法的代码逻辑。也可以看到这里使用的是一个环绕通知。

测试：

$ curl http://localhost:8088/tx1
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    78    0    78    0     0      6      0 --:--:--  0:00:12 --:--:--    21{"success":false,"data":null,"msg":"系统内部错误","errorCode":"u200000"}

主要做的事情如下:

(1) 获取TransactionAttribute 对象, 获取到的对象如下：

tas.getTransactionAttribute(method, targetClass) 获取事务属性，实际最终也是调用方法 org.springframework.transaction.interceptor.AbstractFallbackTransactionAttributeSource#getTransactionAttribute 从org.springframework.transaction.interceptor.AbstractFallbackTransactionAttributeSource#attributeCache 获取

(2) createTransactionIfNecessary方法准备事务相关东西

org.springframework.transaction.interceptor.TransactionAspectSupport#createTransactionIfNecessary 方法源码如下：

    protected TransactionInfo createTransactionIfNecessary(@Nullable PlatformTransactionManager tm,
            @Nullable TransactionAttribute txAttr, final String joinpointIdentification) {

        // If no name specified, apply method identification as transaction name.
        if (txAttr != null && txAttr.getName() == null) {
            txAttr = new DelegatingTransactionAttribute(txAttr) {
                @Override
                public String getName() {
                    return joinpointIdentification;
                }
            };
        }

        TransactionStatus status = null;
        if (txAttr != null) {
            if (tm != null) {
                status = tm.getTransaction(txAttr);
            }
            else {
                if (logger.isDebugEnabled()) {
                    logger.debug("Skipping transactional joinpoint [" + joinpointIdentification +
                            "] because no transaction manager has been configured");
                }
            }
        }
        return prepareTransactionInfo(tm, txAttr, joinpointIdentification, status);
    }

tm.getTransaction(txAttr); 方法调用org.springframework.transaction.support.AbstractPlatformTransactionManager#getTransaction 获取事务

    @Override
    public final TransactionStatus getTransaction(@Nullable TransactionDefinition definition)
            throws TransactionException {

        // Use defaults if no transaction definition given.
        TransactionDefinition def = (definition != null ? definition : TransactionDefinition.withDefaults());

        Object transaction = doGetTransaction();
        boolean debugEnabled = logger.isDebugEnabled();

        if (isExistingTransaction(transaction)) {
            // Existing transaction found -> check propagation behavior to find out how to behave.
            return handleExistingTransaction(def, transaction, debugEnabled);
        }

        // Check definition settings for new transaction.
        if (def.getTimeout() < TransactionDefinition.TIMEOUT_DEFAULT) {
            throw new InvalidTimeoutException("Invalid transaction timeout", def.getTimeout());
        }

        // No existing transaction found -> check propagation behavior to find out how to proceed.
        if (def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_MANDATORY) {
            throw new IllegalTransactionStateException(
                    "No existing transaction found for transaction marked with propagation 'mandatory'");
        }
        else if (def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRED ||
                def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW ||
                def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
            SuspendedResourcesHolder suspendedResources = suspend(null);
            if (debugEnabled) {
                logger.debug("Creating new transaction with name [" + def.getName() + "]: " + def);
            }
            try {
                return startTransaction(def, transaction, debugEnabled, suspendedResources);
            }
            catch (RuntimeException | Error ex) {
                resume(null, suspendedResources);
                throw ex;
            }
        }
        else {
            // Create "empty" transaction: no actual transaction, but potentially synchronization.
            if (def.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT && logger.isWarnEnabled()) {
                logger.warn("Custom isolation level specified but no actual transaction initiated; " +
                        "isolation level will effectively be ignored: " + def);
            }
            boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
            return prepareTransactionStatus(def, null, true, newSynchronization, debugEnabled, null);
        }
    }

这里会判断是否有事务，没有事务的情况下判断事务的传播行为，然后会调用org.springframework.transaction.support.AbstractPlatformTransactionManager#startTransaction开启事务

    private TransactionStatus startTransaction(TransactionDefinition definition, Object transaction,
            boolean debugEnabled, @Nullable SuspendedResourcesHolder suspendedResources) {

        boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
        DefaultTransactionStatus status = newTransactionStatus(
                definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
        doBegin(transaction, definition);
        prepareSynchronization(status, definition);
        return status;
    }

　　首先创建DefaultTransactionStatus 会记录事务的一些属性到该对象;然后调用 org.springframework.jdbc.datasource.DataSourceTransactionManager#doBegin 开启事务

    protected void doBegin(Object transaction, TransactionDefinition definition) {
        DataSourceTransactionManager.DataSourceTransactionObject txObject = (DataSourceTransactionManager.DataSourceTransactionObject)transaction;
        Connection con = null;

        try {
            if (!txObject.hasConnectionHolder() || txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
                Connection newCon = this.obtainDataSource().getConnection();
                if (this.logger.isDebugEnabled()) {
                    this.logger.debug("Acquired Connection [" + newCon + "] for JDBC transaction");
                }

                txObject.setConnectionHolder(new ConnectionHolder(newCon), true);
            }

            txObject.getConnectionHolder().setSynchronizedWithTransaction(true);
            con = txObject.getConnectionHolder().getConnection();
            Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
            txObject.setPreviousIsolationLevel(previousIsolationLevel);
            txObject.setReadOnly(definition.isReadOnly());
            if (con.getAutoCommit()) {
                txObject.setMustRestoreAutoCommit(true);
                if (this.logger.isDebugEnabled()) {
                    this.logger.debug("Switching JDBC Connection [" + con + "] to manual commit");
                }

                con.setAutoCommit(false);
            }

            this.prepareTransactionalConnection(con, definition);
            txObject.getConnectionHolder().setTransactionActive(true);
            int timeout = this.determineTimeout(definition);
            if (timeout != -1) {
                txObject.getConnectionHolder().setTimeoutInSeconds(timeout);
            }

            if (txObject.isNewConnectionHolder()) {
                TransactionSynchronizationManager.bindResource(this.obtainDataSource(), txObject.getConnectionHolder());
            }

        } catch (Throwable var7) {
            if (txObject.isNewConnectionHolder()) {
                DataSourceUtils.releaseConnection(con, this.obtainDataSource());
                txObject.setConnectionHolder((ConnectionHolder)null, false);
            }

            throw new CannotCreateTransactionException("Could not open JDBC Connection for transaction", var7);
        }
    }

做完上面操作然后调用org.springframework.transaction.interceptor.TransactionAspectSupport#prepareTransactionInfo 将相关信息封装到一个TransactionInfo 对象中:创建对象，然后txInfo.bindToThread与当前线程进行绑定(ThreadLocal)

    protected TransactionInfo prepareTransactionInfo(@Nullable PlatformTransactionManager tm,
            @Nullable TransactionAttribute txAttr, String joinpointIdentification,
            @Nullable TransactionStatus status) {

        TransactionInfo txInfo = new TransactionInfo(tm, txAttr, joinpointIdentification);
        if (txAttr != null) {
            // We need a transaction for this method...
            if (logger.isTraceEnabled()) {
                logger.trace("Getting transaction for [" + txInfo.getJoinpointIdentification() + "]");
            }
            // The transaction manager will flag an error if an incompatible tx already exists.
            txInfo.newTransactionStatus(status);
        }
        else {
            // The TransactionInfo.hasTransaction() method will return false. We created it only
            // to preserve the integrity of the ThreadLocal stack maintained in this class.
            if (logger.isTraceEnabled()) {
                logger.trace("No need to create transaction for [" + joinpointIdentification +
                        "]: This method is not transactional.");
            }
        }

        // We always bind the TransactionInfo to the thread, even if we didn't create
        // a new transaction here. This guarantees that the TransactionInfo stack
        // will be managed correctly even if no transaction was created by this aspect.
        txInfo.bindToThread();
        return txInfo;
    }

(3) 调用业务方法

invocation.proceedWithInvocation();

(4) 如果捕捉到异常之后调用方法completeTransactionAfterThrowing 进行事务异常处理；然后将异常再向外抛(finally代码块清掉事务相关状态)

org.springframework.transaction.interceptor.TransactionAspectSupport#completeTransactionAfterThrowing 如下：

    protected void completeTransactionAfterThrowing(@Nullable TransactionInfo txInfo, Throwable ex) {
        if (txInfo != null && txInfo.getTransactionStatus() != null) {
            if (logger.isTraceEnabled()) {
                logger.trace("Completing transaction for [" + txInfo.getJoinpointIdentification() +
                        "] after exception: " + ex);
            }
            if (txInfo.transactionAttribute != null && txInfo.transactionAttribute.rollbackOn(ex)) {
                try {
                    txInfo.getTransactionManager().rollback(txInfo.getTransactionStatus());
                }
                catch (TransactionSystemException ex2) {
                    logger.error("Application exception overridden by rollback exception", ex);
                    ex2.initApplicationException(ex);
                    throw ex2;
                }
                catch (RuntimeException | Error ex2) {
                    logger.error("Application exception overridden by rollback exception", ex);
                    throw ex2;
                }
            }
            else {
                // We don't roll back on this exception.
                // Will still roll back if TransactionStatus.isRollbackOnly() is true.
                try {
                    txInfo.getTransactionManager().commit(txInfo.getTransactionStatus());
                }
                catch (TransactionSystemException ex2) {
                    logger.error("Application exception overridden by commit exception", ex);
                    ex2.initApplicationException(ex);
                    throw ex2;
                }
                catch (RuntimeException | Error ex2) {
                    logger.error("Application exception overridden by commit exception", ex);
                    throw ex2;
                }
            }
        }
    }

如果是支持回滚的异常类型会进行回滚， org.springframework.transaction.interceptor.DefaultTransactionAttribute#rollbackOn方法如下：(也就是默认是Error 和 RuntimeException 类型的异常会进行回滚)

    public boolean rollbackOn(Throwable ex) {
        return (ex instanceof RuntimeException || ex instanceof Error);
    }

调用org.springframework.transaction.support.AbstractPlatformTransactionManager#rollback 进行回滚：

    public final void rollback(TransactionStatus status) throws TransactionException {
        if (status.isCompleted()) {
            throw new IllegalTransactionStateException(
                    "Transaction is already completed - do not call commit or rollback more than once per transaction");
        }

        DefaultTransactionStatus defStatus = (DefaultTransactionStatus) status;
        processRollback(defStatus, false);
    }

org.springframework.transaction.support.AbstractPlatformTransactionManager#processRollback:

    private void processRollback(DefaultTransactionStatus status, boolean unexpected) {
        try {
            boolean unexpectedRollback = unexpected;

            try {
                triggerBeforeCompletion(status);

                if (status.hasSavepoint()) {
                    if (status.isDebug()) {
                        logger.debug("Rolling back transaction to savepoint");
                    }
                    status.rollbackToHeldSavepoint();
                }
                else if (status.isNewTransaction()) {
                    if (status.isDebug()) {
                        logger.debug("Initiating transaction rollback");
                    }
                    doRollback(status);
                }
                else {
                    // Participating in larger transaction
                    if (status.hasTransaction()) {
                        if (status.isLocalRollbackOnly() || isGlobalRollbackOnParticipationFailure()) {
                            if (status.isDebug()) {
                                logger.debug("Participating transaction failed - marking existing transaction as rollback-only");
                            }
                            doSetRollbackOnly(status);
                        }
                        else {
                            if (status.isDebug()) {
                                logger.debug("Participating transaction failed - letting transaction originator decide on rollback");
                            }
                        }
                    }
                    else {
                        logger.debug("Should roll back transaction but cannot - no transaction available");
                    }
                    // Unexpected rollback only matters here if we're asked to fail early
                    if (!isFailEarlyOnGlobalRollbackOnly()) {
                        unexpectedRollback = false;
                    }
                }
            }
            catch (RuntimeException | Error ex) {
                triggerAfterCompletion(status, TransactionSynchronization.STATUS_UNKNOWN);
                throw ex;
            }

            triggerAfterCompletion(status, TransactionSynchronization.STATUS_ROLLED_BACK);

            // Raise UnexpectedRollbackException if we had a global rollback-only marker
            if (unexpectedRollback) {
                throw new UnexpectedRollbackException(
                        "Transaction rolled back because it has been marked as rollback-only");
            }
        }
        finally {
            cleanupAfterCompletion(status);
        }
    }

最终调用到： org.springframework.jdbc.datasource.DataSourceTransactionManager#doRollback 进行回滚：

    protected void doRollback(DefaultTransactionStatus status) {
        DataSourceTransactionObject txObject = (DataSourceTransactionObject) status.getTransaction();
        Connection con = txObject.getConnectionHolder().getConnection();
        if (status.isDebug()) {
            logger.debug("Rolling back JDBC transaction on Connection [" + con + "]");
        }
        try {
            con.rollback();
        }
        catch (SQLException ex) {
            throw new TransactionSystemException("Could not roll back JDBC transaction", ex);
        }
    }

(5) 如果没有捕捉到异常，finally代码块清掉事务相关状态；然后对事务进行commit。

org.springframework.transaction.interceptor.TransactionAspectSupport#commitTransactionAfterReturning:

    protected void commitTransactionAfterReturning(@Nullable TransactionInfo txInfo) {
        if (txInfo != null && txInfo.getTransactionStatus() != null) {
            if (logger.isTraceEnabled()) {
                logger.trace("Completing transaction for [" + txInfo.getJoinpointIdentification() + "]");
            }
            txInfo.getTransactionManager().commit(txInfo.getTransactionStatus());
        }
    }

org.springframework.transaction.support.AbstractPlatformTransactionManager#commit:

    public final void commit(TransactionStatus status) throws TransactionException {
        if (status.isCompleted()) {
            throw new IllegalTransactionStateException(
                    "Transaction is already completed - do not call commit or rollback more than once per transaction");
        }

        DefaultTransactionStatus defStatus = (DefaultTransactionStatus) status;
        if (defStatus.isLocalRollbackOnly()) {
            if (defStatus.isDebug()) {
                logger.debug("Transactional code has requested rollback");
            }
            processRollback(defStatus, false);
            return;
        }

        if (!shouldCommitOnGlobalRollbackOnly() && defStatus.isGlobalRollbackOnly()) {
            if (defStatus.isDebug()) {
                logger.debug("Global transaction is marked as rollback-only but transactional code requested commit");
            }
            processRollback(defStatus, true);
            return;
        }

        processCommit(defStatus);
    }

org.springframework.transaction.support.AbstractPlatformTransactionManager#processCommit:

    private void processCommit(DefaultTransactionStatus status) throws TransactionException {
        try {
            boolean beforeCompletionInvoked = false;

            try {
                boolean unexpectedRollback = false;
                prepareForCommit(status);
                triggerBeforeCommit(status);
                triggerBeforeCompletion(status);
                beforeCompletionInvoked = true;

                if (status.hasSavepoint()) {
                    if (status.isDebug()) {
                        logger.debug("Releasing transaction savepoint");
                    }
                    unexpectedRollback = status.isGlobalRollbackOnly();
                    status.releaseHeldSavepoint();
                }
                else if (status.isNewTransaction()) {
                    if (status.isDebug()) {
                        logger.debug("Initiating transaction commit");
                    }
                    unexpectedRollback = status.isGlobalRollbackOnly();
                    doCommit(status);
                }
                else if (isFailEarlyOnGlobalRollbackOnly()) {
                    unexpectedRollback = status.isGlobalRollbackOnly();
                }

                // Throw UnexpectedRollbackException if we have a global rollback-only
                // marker but still didn't get a corresponding exception from commit.
                if (unexpectedRollback) {
                    throw new UnexpectedRollbackException(
                            "Transaction silently rolled back because it has been marked as rollback-only");
                }
            }
            catch (UnexpectedRollbackException ex) {
                // can only be caused by doCommit
                triggerAfterCompletion(status, TransactionSynchronization.STATUS_ROLLED_BACK);
                throw ex;
            }
            catch (TransactionException ex) {
                // can only be caused by doCommit
                if (isRollbackOnCommitFailure()) {
                    doRollbackOnCommitException(status, ex);
                }
                else {
                    triggerAfterCompletion(status, TransactionSynchronization.STATUS_UNKNOWN);
                }
                throw ex;
            }
            catch (RuntimeException | Error ex) {
                if (!beforeCompletionInvoked) {
                    triggerBeforeCompletion(status);
                }
                doRollbackOnCommitException(status, ex);
                throw ex;
            }

            // Trigger afterCommit callbacks, with an exception thrown there
            // propagated to callers but the transaction still considered as committed.
            try {
                triggerAfterCommit(status);
            }
            finally {
                triggerAfterCompletion(status, TransactionSynchronization.STATUS_COMMITTED);
            }

        }
        finally {
            cleanupAfterCompletion(status);
        }
    }

　　可以看到最后也是调用doCommit(status);保存事务信息。org.springframework.jdbc.datasource.DataSourceTransactionManager#doCommit：

    protected void doCommit(DefaultTransactionStatus status) {
        DataSourceTransactionManager.DataSourceTransactionObject txObject = (DataSourceTransactionManager.DataSourceTransactionObject)status.getTransaction();
        Connection con = txObject.getConnectionHolder().getConnection();
        if (status.isDebug()) {
            this.logger.debug("Committing JDBC transaction on Connection [" + con + "]");
        }

        try {
            con.commit();
        } catch (SQLException var5) {
            throw new TransactionSystemException("Could not commit JDBC transaction", var5);
        }
    }

总结：事务过程中几个重要的类

(1) org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration 事务自动配置的相关类

(2) org.springframework.transaction.interceptor.BeanFactoryTransactionAttributeSourceAdvisor 可以理解为切面Aspect的角色(内部维护Point与Advisor)

(3) org.springframework.transaction.interceptor.TransactionAttributeSource 用于获取TransactionAttribute 事务属性，也就是读取@Transactional 注解上的相关属性

(4) org.springframework.transaction.interceptor.TransactionAttributeSourcePointcut#TransactionAttributeSourcePointcut (是否需要进行事务的控制是在这个类进行判断的)

(5) org.springframework.transaction.interceptor.TransactionInterceptor 事务拦截器。 (对事务的处理是在这个类)

(6) org.springframework.transaction.interceptor.TransactionAttribute 封装事物属性的接口，也就是封装@Transactional 注解上面的属性

(7) org.springframework.transaction.interceptor.TransactionAspectSupport.TransactionInfo 封装事务信息的类，里面包括的重要属性如下：

        @Nullable
        private final PlatformTransactionManager transactionManager;

        @Nullable
        private final TransactionAttribute transactionAttribute;

        private final String joinpointIdentification;

        @Nullable
        private TransactionStatus transactionStatus;

        @Nullable
        private TransactionInfo oldTransactionInfo;

(8) org.springframework.transaction.TransactionManager 事务管理器。操作事务的方法都在这个类里面。用的最多的是org.springframework.transaction.PlatformTransactionManager 接口的实现类

补充：测试org.springframework.core.annotation.AnnotatedElementUtils#findMergedAnnotationAttributes 方法可以获取接口上的注解

1. 注解类

package com.xm.ggn.test.annotation;

import java.lang.annotation.*;

@Inherited
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnno1 {

    String value() default "111222";
}

2. 接口

package com.xm.ggn.test.annotation;

@MyAnno1("123456")
public interface Interface1 {

    void fun1();
}

3. 类1

package com.xm.ggn.test.annotation;

public class Class1 implements Interface1{

    @Override
    public void fun1() {
        System.out.println("fun1 called!!!");
    }
}

4. Client

package com.xm.ggn.test.annotation;

import org.springframework.core.annotation.AnnotatedElementUtils;
import org.springframework.core.annotation.AnnotationAttributes;

public class Client {

    public static void main(String[] args) {
        AnnotationAttributes attributes = AnnotatedElementUtils.findMergedAnnotationAttributes(
                Class1.class, MyAnno1.class, false, false);
        System.out.println(attributes);
    }
}

5. 测试结果：

补充：javax包下和Spring包下面注解@Transactional的区别

　　两者都可以实现事务的功能，是使用了两个不同的parser来进行解析。

(1) javax包下的@Transactional 注解如下： javax 提供的注解，没有提供指定隔离级别、是否只读等参数，隔离级别也是数据库默认的隔离级别、只读默认是false。参考：org.springframework.transaction.annotation.JtaTransactionAnnotationParser#parseTransactionAnnotation(java.lang.reflect.AnnotatedElement) 创建的时候默认继承自org.springframework.transaction.support.DefaultTransactionDefinition#isolationLevel

package javax.transaction;

import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import javax.enterprise.util.Nonbinding;
import javax.interceptor.InterceptorBinding;

@Inherited
@InterceptorBinding
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Transactional {
    Transactional.TxType value() default Transactional.TxType.REQUIRED;

    @Nonbinding
    Class[] rollbackOn() default {};

    @Nonbinding
    Class[] dontRollbackOn() default {};

    public static enum TxType {
        REQUIRED,
        REQUIRES_NEW,
        MANDATORY,
        SUPPORTS,
        NOT_SUPPORTED,
        NEVER;

        private TxType() {
        }
    }
}

(2) Spring 包下的Transactional 注解如下：解析方法为 org.springframework.transaction.annotation.SpringTransactionAnnotationParser#parseTransactionAnnotation(java.lang.reflect.AnnotatedElement)

package org.springframework.transaction.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.core.annotation.AliasFor;
import org.springframework.transaction.TransactionDefinition;

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Transactional {

    @AliasFor("transactionManager")
    String value() default "";

    @AliasFor("value")
    String transactionManager() default "";

    Propagation propagation() default Propagation.REQUIRED;

    Isolation isolation() default Isolation.DEFAULT;

    int timeout() default TransactionDefinition.TIMEOUT_DEFAULT;

    boolean readOnly() default false;

    Class<? extends Throwable>[] rollbackFor() default {};

    String[] rollbackForClassName() default {};

    Class<? extends Throwable>[] noRollbackFor() default {};

    String[] noRollbackForClassName() default {};

}

补充：TransactionAttribute继承自接口 TransactionDefinition, TransactionDefinition 接口定义了事务传播行为和隔离级别的一些变量：

package org.springframework.transaction;

import org.springframework.lang.Nullable;

/**
 * Interface that defines Spring-compliant transaction properties.
 * Based on the propagation behavior definitions analogous to EJB CMT attributes.
 *
 * <p>Note that isolation level and timeout settings will not get applied unless
 * an actual new transaction gets started. As only {@link #PROPAGATION_REQUIRED},
 * {@link #PROPAGATION_REQUIRES_NEW} and {@link #PROPAGATION_NESTED} can cause
 * that, it usually doesn't make sense to specify those settings in other cases.
 * Furthermore, be aware that not all transaction managers will support those
 * advanced features and thus might throw corresponding exceptions when given
 * non-default values.
 *
 * <p>The {@link #isReadOnly() read-only flag} applies to any transaction context,
 * whether backed by an actual resource transaction or operating non-transactionally
 * at the resource level. In the latter case, the flag will only apply to managed
 * resources within the application, such as a Hibernate {@code Session}.
 *
 * @author Juergen Hoeller
 * @since 08.05.2003
 * @see PlatformTransactionManager#getTransaction(TransactionDefinition)
 * @see org.springframework.transaction.support.DefaultTransactionDefinition
 * @see org.springframework.transaction.interceptor.TransactionAttribute
 */
public interface TransactionDefinition {

    /**
     * Support a current transaction; create a new one if none exists.
     * Analogous to the EJB transaction attribute of the same name.
     * <p>This is typically the default setting of a transaction definition,
     * and typically defines a transaction synchronization scope.
     */
    int PROPAGATION_REQUIRED = 0;

    /**
     * Support a current transaction; execute non-transactionally if none exists.
     * Analogous to the EJB transaction attribute of the same name.
     * <p><b>NOTE:</b> For transaction managers with transaction synchronization,
     * {@code PROPAGATION_SUPPORTS} is slightly different from no transaction
     * at all, as it defines a transaction scope that synchronization might apply to.
     * As a consequence, the same resources (a JDBC {@code Connection}, a
     * Hibernate {@code Session}, etc) will be shared for the entire specified
     * scope. Note that the exact behavior depends on the actual synchronization
     * configuration of the transaction manager!
     * <p>In general, use {@code PROPAGATION_SUPPORTS} with care! In particular, do
     * not rely on {@code PROPAGATION_REQUIRED} or {@code PROPAGATION_REQUIRES_NEW}
     * <i>within</i> a {@code PROPAGATION_SUPPORTS} scope (which may lead to
     * synchronization conflicts at runtime). If such nesting is unavoidable, make sure
     * to configure your transaction manager appropriately (typically switching to
     * "synchronization on actual transaction").
     * @see org.springframework.transaction.support.AbstractPlatformTransactionManager#setTransactionSynchronization
     * @see org.springframework.transaction.support.AbstractPlatformTransactionManager#SYNCHRONIZATION_ON_ACTUAL_TRANSACTION
     */
    int PROPAGATION_SUPPORTS = 1;

    /**
     * Support a current transaction; throw an exception if no current transaction
     * exists. Analogous to the EJB transaction attribute of the same name.
     * <p>Note that transaction synchronization within a {@code PROPAGATION_MANDATORY}
     * scope will always be driven by the surrounding transaction.
     */
    int PROPAGATION_MANDATORY = 2;

    /**
     * Create a new transaction, suspending the current transaction if one exists.
     * Analogous to the EJB transaction attribute of the same name.
     * <p><b>NOTE:</b> Actual transaction suspension will not work out-of-the-box
     * on all transaction managers. This in particular applies to
     * {@link org.springframework.transaction.jta.JtaTransactionManager},
     * which requires the {@code javax.transaction.TransactionManager} to be
     * made available it to it (which is server-specific in standard Java EE).
     * <p>A {@code PROPAGATION_REQUIRES_NEW} scope always defines its own
     * transaction synchronizations. Existing synchronizations will be suspended
     * and resumed appropriately.
     * @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager
     */
    int PROPAGATION_REQUIRES_NEW = 3;

    /**
     * Do not support a current transaction; rather always execute non-transactionally.
     * Analogous to the EJB transaction attribute of the same name.
     * <p><b>NOTE:</b> Actual transaction suspension will not work out-of-the-box
     * on all transaction managers. This in particular applies to
     * {@link org.springframework.transaction.jta.JtaTransactionManager},
     * which requires the {@code javax.transaction.TransactionManager} to be
     * made available it to it (which is server-specific in standard Java EE).
     * <p>Note that transaction synchronization is <i>not</i> available within a
     * {@code PROPAGATION_NOT_SUPPORTED} scope. Existing synchronizations
     * will be suspended and resumed appropriately.
     * @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager
     */
    int PROPAGATION_NOT_SUPPORTED = 4;

    /**
     * Do not support a current transaction; throw an exception if a current transaction
     * exists. Analogous to the EJB transaction attribute of the same name.
     * <p>Note that transaction synchronization is <i>not</i> available within a
     * {@code PROPAGATION_NEVER} scope.
     */
    int PROPAGATION_NEVER = 5;

    /**
     * Execute within a nested transaction if a current transaction exists,
     * behave like {@link #PROPAGATION_REQUIRED} otherwise. There is no
     * analogous feature in EJB.
     * <p><b>NOTE:</b> Actual creation of a nested transaction will only work on
     * specific transaction managers. Out of the box, this only applies to the JDBC
     * {@link org.springframework.jdbc.datasource.DataSourceTransactionManager}
     * when working on a JDBC 3.0 driver. Some JTA providers might support
     * nested transactions as well.
     * @see org.springframework.jdbc.datasource.DataSourceTransactionManager
     */
    int PROPAGATION_NESTED = 6;


    /**
     * Use the default isolation level of the underlying datastore.
     * All other levels correspond to the JDBC isolation levels.
     * @see java.sql.Connection
     */
    int ISOLATION_DEFAULT = -1;

    /**
     * Indicates that dirty reads, non-repeatable reads and phantom reads
     * can occur.
     * <p>This level allows a row changed by one transaction to be read by another
     * transaction before any changes in that row have been committed (a "dirty read").
     * If any of the changes are rolled back, the second transaction will have
     * retrieved an invalid row.
     * @see java.sql.Connection#TRANSACTION_READ_UNCOMMITTED
     */
    int ISOLATION_READ_UNCOMMITTED = 1;  // same as java.sql.Connection.TRANSACTION_READ_UNCOMMITTED;

    /**
     * Indicates that dirty reads are prevented; non-repeatable reads and
     * phantom reads can occur.
     * <p>This level only prohibits a transaction from reading a row
     * with uncommitted changes in it.
     * @see java.sql.Connection#TRANSACTION_READ_COMMITTED
     */
    int ISOLATION_READ_COMMITTED = 2;  // same as java.sql.Connection.TRANSACTION_READ_COMMITTED;

    /**
     * Indicates that dirty reads and non-repeatable reads are prevented;
     * phantom reads can occur.
     * <p>This level prohibits a transaction from reading a row with uncommitted changes
     * in it, and it also prohibits the situation where one transaction reads a row,
     * a second transaction alters the row, and the first transaction re-reads the row,
     * getting different values the second time (a "non-repeatable read").
     * @see java.sql.Connection#TRANSACTION_REPEATABLE_READ
     */
    int ISOLATION_REPEATABLE_READ = 4;  // same as java.sql.Connection.TRANSACTION_REPEATABLE_READ;

    /**
     * Indicates that dirty reads, non-repeatable reads and phantom reads
     * are prevented.
     * <p>This level includes the prohibitions in {@link #ISOLATION_REPEATABLE_READ}
     * and further prohibits the situation where one transaction reads all rows that
     * satisfy a {@code WHERE} condition, a second transaction inserts a row
     * that satisfies that {@code WHERE} condition, and the first transaction
     * re-reads for the same condition, retrieving the additional "phantom" row
     * in the second read.
     * @see java.sql.Connection#TRANSACTION_SERIALIZABLE
     */
    int ISOLATION_SERIALIZABLE = 8;  // same as java.sql.Connection.TRANSACTION_SERIALIZABLE;


    /**
     * Use the default timeout of the underlying transaction system,
     * or none if timeouts are not supported.
     */
    int TIMEOUT_DEFAULT = -1;


    /**
     * Return the propagation behavior.
     * <p>Must return one of the {@code PROPAGATION_XXX} constants
     * defined on {@link TransactionDefinition this interface}.
     * <p>The default is {@link #PROPAGATION_REQUIRED}.
     * @return the propagation behavior
     * @see #PROPAGATION_REQUIRED
     * @see org.springframework.transaction.support.TransactionSynchronizationManager#isActualTransactionActive()
     */
    default int getPropagationBehavior() {
        return PROPAGATION_REQUIRED;
    }

    /**
     * Return the isolation level.
     * <p>Must return one of the {@code ISOLATION_XXX} constants defined on
     * {@link TransactionDefinition this interface}. Those constants are designed
     * to match the values of the same constants on {@link java.sql.Connection}.
     * <p>Exclusively designed for use with {@link #PROPAGATION_REQUIRED} or
     * {@link #PROPAGATION_REQUIRES_NEW} since it only applies to newly started
     * transactions. Consider switching the "validateExistingTransactions" flag to
     * "true" on your transaction manager if you'd like isolation level declarations
     * to get rejected when participating in an existing transaction with a different
     * isolation level.
     * <p>The default is {@link #ISOLATION_DEFAULT}. Note that a transaction manager
     * that does not support custom isolation levels will throw an exception when
     * given any other level than {@link #ISOLATION_DEFAULT}.
     * @return the isolation level
     * @see #ISOLATION_DEFAULT
     * @see org.springframework.transaction.support.AbstractPlatformTransactionManager#setValidateExistingTransaction
     */
    default int getIsolationLevel() {
        return ISOLATION_DEFAULT;
    }

    /**
     * Return the transaction timeout.
     * <p>Must return a number of seconds, or {@link #TIMEOUT_DEFAULT}.
     * <p>Exclusively designed for use with {@link #PROPAGATION_REQUIRED} or
     * {@link #PROPAGATION_REQUIRES_NEW} since it only applies to newly started
     * transactions.
     * <p>Note that a transaction manager that does not support timeouts will throw
     * an exception when given any other timeout than {@link #TIMEOUT_DEFAULT}.
     * <p>The default is {@link #TIMEOUT_DEFAULT}.
     * @return the transaction timeout
     */
    default int getTimeout() {
        return TIMEOUT_DEFAULT;
    }

    /**
     * Return whether to optimize as a read-only transaction.
     * <p>The read-only flag applies to any transaction context, whether backed
     * by an actual resource transaction ({@link #PROPAGATION_REQUIRED}/
     * {@link #PROPAGATION_REQUIRES_NEW}) or operating non-transactionally at
     * the resource level ({@link #PROPAGATION_SUPPORTS}). In the latter case,
     * the flag will only apply to managed resources within the application,
     * such as a Hibernate {@code Session}.
     * <p>This just serves as a hint for the actual transaction subsystem;
     * it will <i>not necessarily</i> cause failure of write access attempts.
     * A transaction manager which cannot interpret the read-only hint will
     * <i>not</i> throw an exception when asked for a read-only transaction.
     * @return {@code true} if the transaction is to be optimized as read-only
     * ({@code false} by default)
     * @see org.springframework.transaction.support.TransactionSynchronization#beforeCommit(boolean)
     * @see org.springframework.transaction.support.TransactionSynchronizationManager#isCurrentTransactionReadOnly()
     */
    default boolean isReadOnly() {
        return false;
    }

    /**
     * Return the name of this transaction. Can be {@code null}.
     * <p>This will be used as the transaction name to be shown in a
     * transaction monitor, if applicable (for example, WebLogic's).
     * <p>In case of Spring's declarative transactions, the exposed name will be
     * the {@code fully-qualified class name + "." + method name} (by default).
     * @return the name of this transaction ({@code null} by default}
     * @see org.springframework.transaction.interceptor.TransactionAspectSupport
     * @see org.springframework.transaction.support.TransactionSynchronizationManager#getCurrentTransactionName()
     */
    @Nullable
    default String getName() {
        return null;
    }


    // Static builder methods

    /**
     * Return an unmodifiable {@code TransactionDefinition} with defaults.
     * <p>For customization purposes, use the modifiable
     * {@link org.springframework.transaction.support.DefaultTransactionDefinition}
     * instead.
     * @since 5.2
     */
    static TransactionDefinition withDefaults() {
        return StaticTransactionDefinition.INSTANCE;
    }

}

【当你用心写完每一篇博客之后,你会发现它比你用代码实现功能更有成就感!】

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原文地址：https://www.cnblogs.com/qlqwjy/p/14706202.html