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spring5.1.x源码解析之八(事务处理)_getcompositetransaction() returning null!

作者：我家自动化 | 2024-04-16 05:47:39

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getcompositetransaction() returning null!

文章目录


Advisor增强器:封装拦截器的获取
PointcutAdvisor:封装Pointcut获得
Pointcut:封装MethodMatcher获得
MethodMatcher:方法匹配
TransactionAttributeSource:提取事务属性
Interceptor:Advice的子类拦截器的获取

导入配置

sql

DROP TABLE IF EXISTS `t_user`;
CREATE TABLE `t_user`  (
  `id` int(11) UNSIGNED NOT NULL AUTO_INCREMENT,
  `name` varchar(64) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT '' COMMENT '用户名',
  `passwd` varchar(64) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT '' COMMENT '密码',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 20 CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

SET FOREIGN_KEY_CHECKS = 1;


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PO

package org.example.jdbc;


import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;


@Data
@AllArgsConstructor
public class User {
    private Long id;
    private String name;
    private String passwd;
}


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配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/tx
        http://www.springframework.org/schema/tx/spring-tx.xsd
                http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd
">
    <bean id="dataSource" class="org.apache.commons.dbcp2.BasicDataSource" destroy-method="close">
        <property name="driverClassName" value="com.mysql.cj.jdbc.Driver"></property>
        <property name="url" value="jdbc:mysql:///test?serverTimezone=UTC"></property>
        <!--<property name="url" value="jdbc:mysql://localhost:3306/test?serverTimezone=UTC"></property>-->
        <property name="username" value="root"></property>
        <property name="password" value="root"></property>
        <property name="initialSize" value="1"></property>
        <property name="maxIdle" value="2"></property>
        <property name="minIdle" value="1"></property>
    </bean>

    <bean id="txManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager" >
        <property name="dataSource" ref="dataSource"></property>
    </bean>
    <tx:annotation-driven transaction-manager="txManager"/>

    <bean id="userService" class="org.example.tx.TXUserServiceImpl">
        <property name="dataSource" ref="dataSource"/>
    </bean>
</beans>

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service

package org.example.tx;

import org.example.jdbc.User;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;

import java.util.List;


public interface TXUserService {
    public void save(User user);

}


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package org.example.tx;

import org.example.jdbc.User;
import org.example.jdbc.UserRowMapper;
import org.example.jdbc.UserService;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;

import javax.sql.DataSource;
import java.sql.Types;
import java.util.List;

//可设置接口,具体实现类,方法上,都生效
@Transactional(propagation = Propagation.REQUIRED)
public class TXUserServiceImpl implements TXUserService   {
    private JdbcTemplate jdbcTemplate;

    public void setDataSource(DataSource dataSource) {
        this.jdbcTemplate = new JdbcTemplate(dataSource);
    }

    @Override
    public void save(User user)  {
        jdbcTemplate.update("insert into t_user(`name`,passwd) values (?,?)",
                new Object[]{user.getName(),user.getPasswd()},
                new int[]{Types.VARCHAR,Types.VARCHAR});
 //只对RuntimeException有效回滚,如果没自定义异常接受的话
        // 后续源码解答
        throw new RuntimeException();
    }

}


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解析tx标签

在这里插入图片描述
进入命名空间解析器,查找annotation-driven对应解析器

	@Override
	public void init() {
		registerBeanDefinitionParser("advice", new TxAdviceBeanDefinitionParser());
		registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());
		registerBeanDefinitionParser("jta-transaction-manager", new JtaTransactionManagerBeanDefinitionParser());
	}

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/*
	注册事务事件监听器
	默认aop-proxy事务切入
	 */
	public BeanDefinition parse(Element element, ParserContext parserContext) {
		//注册事务事件监听器
		registerTransactionalEventListenerFactory(parserContext);
		String mode = element.getAttribute("mode");
		if ("aspectj".equals(mode)) {
			// mode="aspectj",使用aspectj进行事务切入
			registerTransactionAspect(element, parserContext);
			if (ClassUtils.isPresent("javax.transaction.Transactional", getClass().getClassLoader())) {
				registerJtaTransactionAspect(element, parserContext);
			}
		}
		else {
			// mode="proxy",默认
			AopAutoProxyConfigurer.configureAutoProxyCreator(element, parserContext);
		}
		return null;
	}

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/*
		注册InfrastructureAdvisorAutoProxyCreator:bean初始化后执行,主要对advisor的处理,封装增强后的对象
		创建sourceDef:接口上是否有事务注解声明进行匹配,以及获取TransactionAttribute
		interceptorDef:进行事务增强
		advisorDef:aop的入口,以及封装sourceDef的获取方法
		创建CompositeComponentDefinition
		 */
		public static void configureAutoProxyCreator(Element element, ParserContext parserContext) {
			//注册InfrastructureAdvisorAutoProxyCreator
			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.
				//创建TransactionAttributeSource bean
				//解析注解
				RootBeanDefinition sourceDef = new RootBeanDefinition(
						"org.springframework.transaction.annotation.AnnotationTransactionAttributeSource");
				sourceDef.setSource(eleSource);
				sourceDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
				//注册bean并使用Spring定义规则生成beanName
				String sourceName = parserContext.getReaderContext().registerWithGeneratedName(sourceDef);

				// Create the TransactionInterceptor definition.
				//创建TransactionInterceptor
				RootBeanDefinition interceptorDef = new RootBeanDefinition(TransactionInterceptor.class);
				interceptorDef.setSource(eleSource);
				interceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
				//RootBeanDefinition设置transactionManagerBeanName
				registerTransactionManager(element, interceptorDef);
				//将sourceName对象注入interceptorDef的transactionAttributeSource属性中
				interceptorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
				String interceptorName = parserContext.getReaderContext().registerWithGeneratedName(interceptorDef);

				// Create the TransactionAttributeSourceAdvisor definition.
				//创建TransactionAttributeSourceAdvisor的bean
				RootBeanDefinition advisorDef = new RootBeanDefinition(BeanFactoryTransactionAttributeSourceAdvisor.class);
				advisorDef.setSource(eleSource);
				advisorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
				//将sourceName对象注入advisor的transactionAttributeSource属性中
				advisorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
				//将interceptorName注入advisor的adviceBeanName属性中
				advisorDef.getPropertyValues().add("adviceBeanName", interceptorName);
				//如果配置了order,则加入bean中
				if (element.hasAttribute("order")) {
					advisorDef.getPropertyValues().add("order", element.getAttribute("order"));
				}
				//注册advisorDef到spring容器
				parserContext.getRegistry().registerBeanDefinition(txAdvisorBeanName, advisorDef);

				//创建CompositeComponentDefinition
				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);
			}
		}

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	/*
	TX事务
	 */
	public static void registerAutoProxyCreatorIfNecessary(
			ParserContext parserContext, Element sourceElement) {

		//注册InfrastructureAdvisorAutoProxyCreator
		BeanDefinition beanDefinition = AopConfigUtils.registerAutoProxyCreatorIfNecessary(
				parserContext.getRegistry(), parserContext.extractSource(sourceElement));
		//对于proxy-target-class以及expose-proxy属性的处理
		useClassProxyingIfNecessary(parserContext.getRegistry(), sourceElement);
		//注册组件并通知,便于监听器做进一步处理
		registerComponentIfNecessary(beanDefinition, parserContext);
	}

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	@Nullable
	public static BeanDefinition registerAutoProxyCreatorIfNecessary(
			BeanDefinitionRegistry registry, @Nullable Object source) {

		//注册InfrastructureAdvisorAutoProxyCreator
		return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
	}


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	/*
	创建org.springframework.aop.config.internalAutoProxyCreator
	 */
	private static BeanDefinition registerOrEscalateApcAsRequired(
			Class<?> cls, BeanDefinitionRegistry registry, @Nullable Object source) {

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

		//如果已经存在了自动代理创建器且存在的创建器与现在的不一致那么需要根据优先级判断到底使用哪个
		if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {
			BeanDefinition apcDefinition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);
			if (!cls.getName().equals(apcDefinition.getBeanClassName())) {
				int currentPriority = findPriorityForClass(apcDefinition.getBeanClassName());
				int requiredPriority = findPriorityForClass(cls);
				//根据优先级判断使用哪个
				if (currentPriority < requiredPriority) {
					//改变bean所对应的className属性
					apcDefinition.setBeanClassName(cls.getName());
				}
			}
			//如果已经存在自动代理创建器并且与将要创建的一致,那么无需创建
			return null;
		}
		//声明AnnotationAwareAspectJAutoProxyCreator注册为新的RootBeanDefinition
		RootBeanDefinition beanDefinition = new RootBeanDefinition(cls);
		beanDefinition.setSource(source);
		beanDefinition.getPropertyValues().add("order", Ordered.HIGHEST_PRECEDENCE);
		beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
		registry.registerBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME, beanDefinition);
		return beanDefinition;
	}

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对advisor的处理,封装增强后的对象

InfrastructureAdvisorAutoProxyCreator

结构层次
在这里插入图片描述
查看继承了BeanPostProcessor接口,其实这个方法在AOP篇已经见过

	/*
	构建key
	封装对象
	 */
	public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
		if (bean != null) {
			//构建key,工厂bean格式&beanName
			Object cacheKey = getCacheKey(bean.getClass(), beanName);
			//创建对象完成后赋值之前,利用工厂创建了bean,同时添加到了earlyProxyReferences进行代理,主要避免循环依赖
			//主要看org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean
			//但该对象创建完成后,表明不在需要利用工厂创建对象,从而避免循环依赖的问题,于是该对象可以删除
			//如果删除对象和bean一致,说明对象一样,不需要进行代理
			if (this.earlyProxyReferences.remove(cacheKey) != bean) {
				//封装指定bean
				return wrapIfNecessary(bean, beanName, cacheKey);
			}
		}
		return bean;
	}

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/*
		获取缓存bean
		判断是否增强
		判断是否基础设施类
		获取增强方法并进行代理
		加入缓存
	 */
	protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
		//如果已经处理过
		if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
			return bean;
		}
		//无需增强
		if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
			return bean;
		}
		//给定的bean类是否代表一个基础设施类,基础设施类不应代理,或者配置了指定的bean不需要代理
		if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
			this.advisedBeans.put(cacheKey, Boolean.FALSE);
			return bean;
		}

		//如果存在增强方法则创建代理
		// Create proxy if we have advice.
		//获取增强方法
		Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
		//如果获取了增强则需要针对增强创建代理
		if (specificInterceptors != DO_NOT_PROXY) {
			this.advisedBeans.put(cacheKey, Boolean.TRUE);
			//创建代理
			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;
	}

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@Override
	@Nullable
	protected Object[] getAdvicesAndAdvisorsForBean(
			Class<?> beanClass, String beanName, @Nullable TargetSource targetSource) {
		//寻找代理切面
		List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
		if (advisors.isEmpty()) {
			return DO_NOT_PROXY;
		}
		return advisors.toArray();
	}

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寻找匹配的增强器

	/*
	寻找匹配的增强器
	并执行子类覆盖扩展
	排序返回
	 */
	protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
		//获取所有增强器
		List<Advisor> candidateAdvisors = findCandidateAdvisors();
		//寻找匹配增强器
		List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
		//执行扩展,子类可覆盖
		extendAdvisors(eligibleAdvisors);
		if (!eligibleAdvisors.isEmpty()) {
			//排序
			eligibleAdvisors = sortAdvisors(eligibleAdvisors);
		}
		return eligibleAdvisors;
	}


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	protected List<Advisor> findCandidateAdvisors() {
		Assert.state(this.advisorRetrievalHelper != null, "No BeanFactoryAdvisorRetrievalHelper available");
		//寻找候选增强器
		return this.advisorRetrievalHelper.findAdvisorBeans();
	}


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在这里一步中,实际上找到了advisorDef这个增强器

public List<Advisor> findAdvisorBeans() {
		// Determine list of advisor bean names, if not cached already.
		String[] advisorNames = this.cachedAdvisorBeanNames;
		if (advisorNames == null) {
			// Do not initialize FactoryBeans here: We need to leave all regular beans
			// uninitialized to let the auto-proxy creator apply to them!
			advisorNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
					this.beanFactory, Advisor.class, true, false);
			this.cachedAdvisorBeanNames = advisorNames;
		}
		if (advisorNames.length == 0) {
			return new ArrayList<>();
		}

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

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匹配增强器

/*
	过滤已经得到的advisors
	 */
	protected List<Advisor> findAdvisorsThatCanApply(
			List<Advisor> candidateAdvisors, Class<?> beanClass, String beanName) {
		//设置当前代理的名称
		ProxyCreationContext.setCurrentProxiedBeanName(beanName);
		try {
			//过滤已经得到的advisors
			return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
		}
		finally {
			//clear代理的名称
			ProxyCreationContext.setCurrentProxiedBeanName(null);
		}
	}

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/*
	空判断
	处理引介增强和普通增强器
	 */
	public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) {
		//空判断
		if (candidateAdvisors.isEmpty()) {
			return candidateAdvisors;
		}
		List<Advisor> eligibleAdvisors = new ArrayList<>();
		//首先处理引介增强,引介增强与其他普通增强处理不一样,所以单独处理
		for (Advisor candidate : candidateAdvisors) {
			if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {
				eligibleAdvisors.add(candidate);
			}
		}
		boolean hasIntroductions = !eligibleAdvisors.isEmpty();
		for (Advisor candidate : candidateAdvisors) {
			//引介增强已经处理
			if (candidate instanceof IntroductionAdvisor) {
				// already processed
				continue;
			}
			//对于普通bean的处理,canApply主要做匹配
			if (canApply(candidate, clazz, hasIntroductions)) {
				eligibleAdvisors.add(candidate);
			}
		}
		return eligibleAdvisors;
	}

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接口上是否有事务注解声明进行匹配,以及获取TransactionAttribute

advisorDef这个增强器的继承结构如下
可以发现继承了PointcutAdvisor这个接口
在这里插入图片描述

/*
	转换成原型并匹配
	 */
	public static boolean canApply(Advisor advisor, Class<?> targetClass, boolean hasIntroductions) {
		if (advisor instanceof IntroductionAdvisor) {
			return ((IntroductionAdvisor) advisor).getClassFilter().matches(targetClass);
		}
		else if (advisor instanceof PointcutAdvisor) {
			PointcutAdvisor pca = (PointcutAdvisor) advisor;
			//事务获取的是这个
			// org.springframework.transaction.interceptor.BeanFactoryTransactionAttributeSourceAdvisor.pointcut
			return canApply(pca.getPointcut(), targetClass, hasIntroductions);
		}
		else {
			// It doesn't have a pointcut so we assume it applies.
			return true;
		}
	}

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这里getPointCut()实际上
在这里插入图片描述
这个transactionAttributeSource实际上就是之前在命名空间解析的时候创建的三个对象
在这里插入图片描述
在这里插入图片描述

/*
	遍历类以及接口所有方法匹配
	 */
	public static boolean canApply(Pointcut pc, Class<?> targetClass, boolean hasIntroductions) {
		Assert.notNull(pc, "Pointcut must not be null");
		if (!pc.getClassFilter().matches(targetClass)) {//默认TrueClassFilter过滤
			return false;
		}

		//此时pc表示TransactionAttributeSourcePointcut
		//pc.getMethodMatcher();返回的是自身
		MethodMatcher methodMatcher = pc.getMethodMatcher();
		if (methodMatcher == MethodMatcher.TRUE) {
			// No need to iterate the methods if we're matching any method anyway...
			return true;
		}

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

		Set<Class<?>> classes = new LinkedHashSet<>();
		if (!Proxy.isProxyClass(targetClass)) {//是否是proxy子类
			classes.add(ClassUtils.getUserClass(targetClass));//获取类,如果是cglib则获取父类
		}
		classes.addAll(ClassUtils.getAllInterfacesForClassAsSet(targetClass));//添加所有接口

		//获取类的所有接口连同本类一起遍历类和方法,匹配成功则加入增强器
		for (Class<?> clazz : classes) {
			Method[] methods = ReflectionUtils.getAllDeclaredMethods(clazz);//获取所有声明方法包括父类
			for (Method method : methods) {
				if (introductionAwareMethodMatcher != null ?
						introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions) :
						//org.springframework.transaction.interceptor.TransactionAttributeSourcePointcut.matches
						methodMatcher.matches(method, targetClass)) {
					return true;
				}
			}
		}

		return false;
	}

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/*
	调用命名空间设置的TransactionAttributeSource解析
	 */
	@Override
	public boolean matches(Method method, Class<?> targetClass) {
		//是否是TransactionalProxy,PlatformTransactionManager,PersistenceExceptionTranslator子类
		if (TransactionalProxy.class.isAssignableFrom(targetClass) ||
				PlatformTransactionManager.class.isAssignableFrom(targetClass) ||
				PersistenceExceptionTranslator.class.isAssignableFrom(targetClass)) {
			return false;
		}
		//命名空间解析的时候注入的,org.springframework.transaction.annotation.AnnotationTransactionAttributeSource
		TransactionAttributeSource tas = getTransactionAttributeSource();
		//匹配
		return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
	}

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/*
	提取事务属性
	 */
	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.
			//提取事务属性
			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;
		}
	}


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	/*
	获取实现方法事务注解并解析,如果没有则从父类,父类没有则从接口获取
	 */
	@Nullable
	protected TransactionAttribute computeTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
		// Don't allow no-public methods as required.
		//非公有方法返回
		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.
		//方法可能在接口上,但我们需要目标class的属性
		//如果目标类是null,这个方法不会被修改
		//specificMethod:实现类中的方法
		Method specificMethod = AopUtils.getMostSpecificMethod(method, targetClass);

		// First try is the method in the target class.
		//查看方法中是否存在事务声明
		TransactionAttribute txAttr = findTransactionAttribute(specificMethod);
		if (txAttr != null) {
			return txAttr;
		}

		// Second try is the transaction attribute on the target class.
		//查看方法所在类中是否存在声明
		txAttr = findTransactionAttribute(specificMethod.getDeclaringClass());
		if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {
			return txAttr;
		}
		//如果存在接口，则去接口中去找
		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;
	}


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查找方法上是否有事务声明

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

protected TransactionAttribute determineTransactionAttribute(AnnotatedElement element) {
		//annotationParsers构造的时候添加默认的
		for (TransactionAnnotationParser annotationParser : this.annotationParsers) {
			TransactionAttribute attr = annotationParser.parseTransactionAnnotation(element);
			if (attr != null) {
				return attr;
			}
		}
		return null;
	}

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@Nullable
	/*
	解析Transactional注解,以及赋值注解属性值
	 */
	public TransactionAttribute parseTransactionAnnotation(AnnotatedElement element) {
		//查看当前类是否有Transactional注解
		AnnotationAttributes attributes = AnnotatedElementUtils.findMergedAnnotationAttributes(
				element, Transactional.class, false, false);
		if (attributes != null) {
			//解析Transactional注解具体属性
			return parseTransactionAnnotation(attributes);
		}
		else {
			return null;
		}
	}

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事务增强

拦截器的注入

因为继承接口,走的aop代理,所以顺着链路,查找拦截器的注入

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

		TargetSource targetSource = this.advised.targetSource;
		Object target = null;

		try {
			//对equals处理
			if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
				// The target does not implement the equals(Object) method itself.
				return equals(args[0]);
			}
			//对hashCode处理
			else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
				// The target does not implement the hashCode() method itself.
				return hashCode();
			}
			else if (method.getDeclaringClass() == DecoratingProxy.class) {
				// There is only getDecoratedClass() declared -> dispatch to proxy config.
				return AopProxyUtils.ultimateTargetClass(this.advised);
			}
			else 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;

			//目标对象内部调用将无法使用切面,则需要暴露代理
			if (this.advised.exposeProxy) {
				// Make invocation available if necessary.
				oldProxy = AopContext.setCurrentProxy(proxy);
				setProxyContext = true;
			}

			// Get as late as possible to minimize the time we "own" the target,
			// in case it comes from a pool.
			target = targetSource.getTarget();
			Class<?> targetClass = (target != null ? target.getClass() : null);

			// Get the interception chain for this method.
			//获取当前方法的拦截器链
			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.
				Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
				//如果没有发现任何拦截器那么直接调用切点方法
				retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
			}
			else {
				// We need to create a method invocation...
				//将拦截器封装ReflectiveMethodInvocation
				//便于使用其proceed进行链接表用拦截器
				MethodInvocation invocation =
						new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
				// Proceed to the joinpoint through the interceptor chain.
				//执行拦截器链,这里主要执行前置和后置等
				retVal = invocation.proceed();
			}

			// Massage return value if necessary.
			Class<?> returnType = method.getReturnType();
			//返回结果
			if (retVal != null && retVal == target &&
					returnType != Object.class && 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.
				//暴露当前代理对象,方便不同事务之间调用的时候，子事务正常启动
				AopContext.setCurrentProxy(oldProxy);
			}
		}
	}


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在这里插入图片描述

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

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@Override
	public List<Object> getInterceptorsAndDynamicInterceptionAdvice(
			Advised config, Method method, @Nullable Class<?> targetClass) {

		// This is somewhat tricky... We have to process introductions first,
		// but we need to preserve order in the ultimate list.
		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;

		for (Advisor advisor : advisors) {
			if (advisor instanceof PointcutAdvisor) {
				// Add it conditionally.
				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) {
						//获取拦截器
						MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
						if (mm.isRuntime()) {
							// Creating a new object instance in the getInterceptors() method
							// isn't a problem as we normally cache created chains.
							for (MethodInterceptor interceptor : interceptors) {
								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;
	}

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在这里插入图片描述

	@Override
	public MethodInterceptor[] getInterceptors(Advisor advisor) throws UnknownAdviceTypeException {
		List<MethodInterceptor> interceptors = new ArrayList<>(3);
		//这里会根据命名空间解析的时候,注入的adviceBeanName进行解析成拦截器
		Advice advice = advisor.getAdvice();
		if (advice instanceof MethodInterceptor) {
			interceptors.add((MethodInterceptor) advice);
		}
		for (AdvisorAdapter adapter : this.adapters) {
			if (adapter.supportsAdvice(advice)) {
				interceptors.add(adapter.getInterceptor(advisor));
			}
		}
		if (interceptors.isEmpty()) {
			throw new UnknownAdviceTypeException(advisor.getAdvice());
		}
		return interceptors.toArray(new MethodInterceptor[0]);
	}

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	@Override
	public Advice getAdvice() {
		Advice advice = this.advice;
		if (advice != null) {
			return advice;
		}

		//断言beanFactory和adviceBeanName不为空
		Assert.state(this.adviceBeanName != null, "'adviceBeanName' must be specified");
		Assert.state(this.beanFactory != null, "BeanFactory must be set to resolve 'adviceBeanName'");

		//是否单例,因为单例才能加入容器
		if (this.beanFactory.isSingleton(this.adviceBeanName)) {
			// Rely on singleton semantics provided by the factory.
			//获取拦截器
			advice = this.beanFactory.getBean(this.adviceBeanName, Advice.class);
			this.advice = advice;
			return advice;
		}
		else {
			// No singleton guarantees from the factory -> let's lock locally but
			// reuse the factory's singleton lock, just in case a lazy dependency
			// of our advice bean happens to trigger the singleton lock implicitly...
			synchronized (this.adviceMonitor) {
				advice = this.advice;
				if (advice == null) {
					advice = this.beanFactory.getBean(this.adviceBeanName, Advice.class);
					this.advice = advice;
				}
				return advice;
			}
		}
	}


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拦截器执行

在这里插入图片描述
不多说,查看结构,分析MethodInterceptor接口方法

/*
	获取目标class
	执行拦截器,并注入下一个拦截器执行链
	 */
	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.
		//获取目标class
		Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);

		// Adapt to TransactionAspectSupport's invokeWithinTransaction...
		return invokeWithinTransaction(invocation.getMethod(), targetClass,
				//执行下一个拦截器执行,保证拦截器链
				invocation::proceed);
	}


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/*
	获取目标class
	 */
	public static Class<?> getTargetClass(Object candidate) {
		Assert.notNull(candidate, "Candidate object must not be null");
		Class<?> result = null;
		//TargetClassAware继承后直接返回目标类
		if (candidate instanceof TargetClassAware) {
			result = ((TargetClassAware) candidate).getTargetClass();
		}
		if (result == null) {
			//判断是否是cglib代理类,如果是获得父类,不是返回当前class
			result = (isCglibProxy(candidate) ? candidate.getClass().getSuperclass() : candidate.getClass());
		}
		return result;
	}

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对事务处理

/*
	对声明式事务和编程式事务处理
	 */
	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();
		//获取对应事务属性
		final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
		//获取beanFactory中的transactionManager
		final PlatformTransactionManager tm = determineTransactionManager(txAttr);
		//构造方法唯一标识(packageName.className.methodName)
		final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);

		//声明式事务处理
		if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
			// Standard transaction demarcation with getTransaction and commit/rollback calls.
			//创建事务
			TransactionInfo txInfo = createTransactionIfNecessary(tm, 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.
				//执行增强方法
				retVal = invocation.proceedWithInvocation();
			}
			catch (Throwable ex) {
				// target invocation exception
				//异常回滚
				completeTransactionAfterThrowing(txInfo, ex);
				throw ex;
			}
			finally {
				//清除信息
				cleanupTransactionInfo(txInfo);
			}
			//提交
			commitTransactionAfterReturning(txInfo);
			return retVal;
		}

		else {
			//编程式事务处理
			final ThrowableHolder throwableHolder = new ThrowableHolder();

			// It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.
			try {
				Object result = ((CallbackPreferringPlatformTransactionManager) tm).execute(txAttr, status -> {
					TransactionInfo txInfo = prepareTransactionInfo(tm, txAttr, joinpointIdentification, status);
					try {
						return invocation.proceedWithInvocation();
					}
					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;
			}
		}
	}

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/*
	封装TransactionAttribute,新增扩展方法
	获取TransactionStatus,内部建立事务
	封装TransactionInfo返回
	 */
	protected TransactionInfo createTransactionIfNecessary(@Nullable PlatformTransactionManager tm,
			@Nullable TransactionAttribute txAttr, final String joinpointIdentification) {

		// If no name specified, apply method identification as transaction name.
		//如果没有名称指定使用方法唯一标识,则使用DelegatingTransactionAttribute封装txAttr
		//内部封装了限定名称和回滚操作
		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) {
				//获取TransactionStatus,内部建立事务
				status = tm.getTransaction(txAttr);
			}
			else {
				if (logger.isDebugEnabled()) {
					logger.debug("Skipping transactional joinpoint [" + joinpointIdentification +
							"] because no transaction manager has been configured");
				}
			}
		}
		//根据指定的属性与status准备一个TransactionInfo
		//TransactionInfo包含目标开始前的所有状态信息,当事务执行失败，方便回滚等后续工作
		return prepareTransactionInfo(tm, txAttr, joinpointIdentification, status);
	}

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	/*
	获取缓存的事务
		如果事务存在,则嵌套事务处理
	事务超时验证
	PropagationBehavior验证
	新建事务
	构建DefaultTransactionStatus返回
	 */
	public final TransactionStatus getTransaction(@Nullable TransactionDefinition definition) throws TransactionException {
		//获取事务,使用的是org.springframework.jdbc.datasource.DataSourceTransactionManager.doGetTransaction
		Object transaction = doGetTransaction();

		// Cache debug flag to avoid repeated checks.
		boolean debugEnabled = logger.isDebugEnabled();

		if (definition == null) {
			// Use defaults if no transaction definition given.
			definition = new DefaultTransactionDefinition();
		}
		//判断当前线程是否存在事务,判断依据为当前线程记录的连接不为空，且连接中(connectionHolder)中的transacationActive属性不为空
		if (isExistingTransaction(transaction)) {
			// Existing transaction found -> check propagation behavior to find out how to behave.
			//当前线程已经存在事务
			//嵌套事务处理
			return handleExistingTransaction(definition, transaction, debugEnabled);
		}

		// Check definition settings for new transaction.
		//事务超时设置验证
		if (definition.getTimeout() < TransactionDefinition.TIMEOUT_DEFAULT) {
			throw new InvalidTimeoutException("Invalid transaction timeout", definition.getTimeout());
		}

		// No existing transaction found -> check propagation behavior to find out how to proceed.
		//如果当前线程不存在事务,且PropagationBehavior被声明为PROPAGATION_MANDATORY,抛出异常
		//PROPAGATION_MANDATORY:当前必须存在一个事务，否则抛出异常。
		if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_MANDATORY) {
			throw new IllegalTransactionStateException(
					"No existing transaction found for transaction marked with propagation 'mandatory'");
		}
		//其他都需要新建事务
		else if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRED ||
				definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW ||
				definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
			//空挂起
			//记录原有事务的状态,便于后续操作对事务的恢复
			SuspendedResourcesHolder suspendedResources = suspend(null);
			if (debugEnabled) {
				logger.debug("Creating new transaction with name [" + definition.getName() + "]: " + definition);
			}
			try {
				//返回此事务管理器是否应激活线程绑定
				//getTransactionSynchronization():默认始终激活事务同步，即使对于“空”事务也是如此
				//SYNCHRONIZATION_NEVER:从不事务同步
				boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
				DefaultTransactionStatus status = newTransactionStatus(
						definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
				/*
				构造transcation,包括设置connectionHandler,隔离级别,timeout
				如果是新连接,绑定当前线程
				 */
				doBegin(transaction, definition);
				//新同步事务的设置,针对的当前线程的设置
				prepareSynchronization(status, definition);
				return status;
			}
			catch (RuntimeException | Error ex) {
				resume(null, suspendedResources);
				throw ex;
			}
		}
		else {
			// Create "empty" transaction: no actual transaction, but potentially synchronization.
			if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT && logger.isWarnEnabled()) {
				logger.warn("Custom isolation level specified but no actual transaction initiated; " +
						"isolation level will effectively be ignored: " + definition);
			}
			boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
			return prepareTransactionStatus(definition, null, true, newSynchronization, debugEnabled, null);
		}
	}


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protected Object doGetTransaction() {
		DataSourceTransactionObject txObject = new DataSourceTransactionObject();
		//设置是否允许保存点,这取决于是否允许嵌套事务
		txObject.setSavepointAllowed(isNestedTransactionAllowed());
		//如果当前线程已经记录数据库连接，则使用原有连接
		ConnectionHolder conHolder =
				(ConnectionHolder) TransactionSynchronizationManager.getResource(obtainDataSource());
		//false:非新创建连接
		txObject.setConnectionHolder(conHolder, false);
		return txObject;
	}

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protected DefaultTransactionStatus newTransactionStatus(
			TransactionDefinition definition, @Nullable Object transaction, boolean newTransaction,
			boolean newSynchronization, boolean debug, @Nullable Object suspendedResources) {

		//true:表示始终激活事务同步且事务没有活动,则打开新的事务同步
		boolean actualNewSynchronization = newSynchronization &&
				//事务活动是否处于活动状态
				!TransactionSynchronizationManager.isSynchronizationActive();
		return new DefaultTransactionStatus(
				transaction, newTransaction, actualNewSynchronization,
				definition.isReadOnly(), debug, suspendedResources);
	}

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	/*
	获取连接
	资源与事务同步
	设置隔离级别以及是否只读
	更改自动提交
	设置是否存在事务,超时时间
	是否通过显式语句只读
	绑定当前线程
	 */
	protected void doBegin(Object transaction, TransactionDefinition definition) {
		DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
		Connection con = null;

		try {
			//connectionHolder不存在以及事务同步设置true,则需要重新获取连接
			if (!txObject.hasConnectionHolder() ||
					txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
				Connection newCon = obtainDataSource().getConnection();
				if (logger.isDebugEnabled()) {
					logger.debug("Acquired Connection [" + newCon + "] for JDBC transaction");
				}
				txObject.setConnectionHolder(new ConnectionHolder(newCon), true);
			}

			//资源与事务同步
			txObject.getConnectionHolder().setSynchronizedWithTransaction(true);
			//获取连接
			con = txObject.getConnectionHolder().getConnection();

			//设置隔离级别以及是否只读
			//只读:提示数据库驱动程序和数据库系统，这个事务并不包含更改数据的操作，
			Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
			txObject.setPreviousIsolationLevel(previousIsolationLevel);

			// Switch to manual commit if necessary. This is very expensive in some JDBC drivers,
			// so we don't want to do it unnecessarily (for example if we've explicitly
			// configured the connection pool to set it already).
			//更改自动提交设置，spring控制提交
			if (con.getAutoCommit()) {
				//用于恢复数据库连接的自动提交属性
				txObject.setMustRestoreAutoCommit(true);
				if (logger.isDebugEnabled()) {
					logger.debug("Switching JDBC Connection [" + con + "] to manual commit");
				}
				con.setAutoCommit(false);
			}

			//是否通过显式语句只读
			prepareTransactionalConnection(con, definition);
			//设置判断当前线程是否存在事务的依据
			txObject.getConnectionHolder().setTransactionActive(true);
			//设置超时时间
			int timeout = determineTimeout(definition);
			if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
				txObject.getConnectionHolder().setTimeoutInSeconds(timeout);
			}

			// Bind the connection holder to the thread.
			if (txObject.isNewConnectionHolder()) {
				//获取连接绑定到当前线程
				TransactionSynchronizationManager.bindResource(obtainDataSource(), txObject.getConnectionHolder());
			}
		}

		catch (Throwable ex) {
			if (txObject.isNewConnectionHolder()) {
				DataSourceUtils.releaseConnection(con, obtainDataSource());
				txObject.setConnectionHolder(null, false);
			}
			throw new CannotCreateTransactionException("Could not open JDBC Connection for transaction", ex);
		}
	}

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@Nullable
	public static Integer prepareConnectionForTransaction(Connection con, @Nullable TransactionDefinition definition)
			throws SQLException {

		Assert.notNull(con, "No Connection specified");

		// Set read-only flag.
		//设置read-only
		if (definition != null &&
				//默认false
				definition.isReadOnly()) {
			try {
				if (logger.isDebugEnabled()) {
					logger.debug("Setting JDBC Connection [" + con + "] read-only");
				}
				con.setReadOnly(true);
			}
			catch (SQLException | RuntimeException ex) {
				Throwable exToCheck = ex;
				while (exToCheck != null) {
					if (exToCheck.getClass().getSimpleName().contains("Timeout")) {
						// Assume it's a connection timeout that would otherwise get lost: e.g. from JDBC 4.0
						throw ex;
					}
					exToCheck = exToCheck.getCause();
				}
				// "read-only not supported" SQLException -> ignore, it's just a hint anyway
				logger.debug("Could not set JDBC Connection read-only", ex);
			}
		}

		// Apply specific isolation level, if any.
		//设置数据库连接的隔离级别
		Integer previousIsolationLevel = null;
		if (definition != null && definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) {
			if (logger.isDebugEnabled()) {
				logger.debug("Changing isolation level of JDBC Connection [" + con + "] to " +
						definition.getIsolationLevel());
			}
			int currentIsolation = con.getTransactionIsolation();
			if (currentIsolation != definition.getIsolationLevel()) {
				previousIsolationLevel = currentIsolation;
				con.setTransactionIsolation(definition.getIsolationLevel());
			}
		}

		return previousIsolationLevel;
	}

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	protected void prepareTransactionalConnection(Connection con, TransactionDefinition definition)
			throws SQLException {

		if (//是否强制性执行事务只读性质,通过显式语句,默认false
				isEnforceReadOnly() &&
				//是否只读
				definition.isReadOnly()) {
			try (Statement stmt = con.createStatement()) {
				stmt.executeUpdate("SET TRANSACTION READ ONLY");
			}
		}
	}

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嵌套事务处理

private TransactionStatus handleExistingTransaction(
			TransactionDefinition definition, Object transaction, boolean debugEnabled)
			throws TransactionException {

		if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NEVER) {
			throw new IllegalTransactionStateException(
					"Existing transaction found for transaction marked with propagation 'never'");
		}

		if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NOT_SUPPORTED) {
			if (debugEnabled) {
				logger.debug("Suspending current transaction");
			}
			Object suspendedResources = suspend(transaction);
			boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
			return prepareTransactionStatus(
					definition, null, false, newSynchronization, debugEnabled, suspendedResources);
		}

		//PROPAGATION_REQUIRES_NEW:创建新的事务
		if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW) {
			if (debugEnabled) {
				logger.debug("Suspending current transaction, creating new transaction with name [" +
						definition.getName() + "]");
			}
			//如果有事务正在执行,则在新事务运行期间挂起
			SuspendedResourcesHolder suspendedResources = suspend(transaction);
			try {
				//建立新事务
				boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
				DefaultTransactionStatus status = newTransactionStatus(
						definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
				doBegin(transaction, definition);
				prepareSynchronization(status, definition);
				return status;
			} catch (RuntimeException | Error beginEx) {
				resumeAfterBeginException(transaction, suspendedResources, beginEx);
				throw beginEx;
			}
		}
		//嵌入事务的处理
		if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
			if (!isNestedTransactionAllowed()) {
				throw new NestedTransactionNotSupportedException(
						"Transaction manager does not allow nested transactions by default - " +
								"specify 'nestedTransactionAllowed' property with value 'true'");
			}
			if (debugEnabled) {
				logger.debug("Creating nested transaction with name [" + definition.getName() + "]");
			}
			if (useSavepointForNestedTransaction()) {
				// Create savepoint within existing Spring-managed transaction,
				// through the SavepointManager API implemented by TransactionStatus.
				// Usually uses JDBC 3.0 savepoints. Never activates Spring synchronization.
				//如果没有可以使用保存点的方式控制事务回滚,那么在嵌入式事务的建立初始建立保存点
				DefaultTransactionStatus status =
						prepareTransactionStatus(definition, transaction, false, false, debugEnabled, null);
				status.createAndHoldSavepoint();
				return status;
			} else {
				// Nested transaction through nested begin and commit/rollback calls.
				// Usually only for JTA: Spring synchronization might get activated here
				// in case of a pre-existing JTA transaction.
				//有些情况不能创建保存点，如JTA,则建立新事务
				boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
				DefaultTransactionStatus status = newTransactionStatus(
						definition, transaction, true, newSynchronization, debugEnabled, null);
				doBegin(transaction, definition);
				prepareSynchronization(status, definition);
				return status;
			}
		}

		// Assumably PROPAGATION_SUPPORTS or PROPAGATION_REQUIRED.
		if (debugEnabled) {
			logger.debug("Participating in existing transaction");
		}
		//是否校验存在事务,默认false
		if (isValidateExistingTransaction()) {
			//如果不是采用底层默认隔离级别
			if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) {
				Integer currentIsolationLevel = TransactionSynchronizationManager.getCurrentTransactionIsolationLevel();
				if (currentIsolationLevel == null || currentIsolationLevel != definition.getIsolationLevel()) {
					Constants isoConstants = DefaultTransactionDefinition.constants;
					throw new IllegalTransactionStateException("Participating transaction with definition [" +
							definition + "] specifies isolation level which is incompatible with existing transaction: " +
							(currentIsolationLevel != null ?
									isoConstants.toCode(currentIsolationLevel, DefaultTransactionDefinition.PREFIX_ISOLATION) :
									"(unknown)"));
				}
			}
			//可以读写
			if (!definition.isReadOnly()) {
				//当前事务管理器只能读
				if (TransactionSynchronizationManager.isCurrentTransactionReadOnly()) {
					throw new IllegalTransactionStateException("Participating transaction with definition [" +
							definition + "] is not marked as read-only but existing transaction is");
				}
			}
		}
		boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
		return prepareTransactionStatus(definition, transaction, false, newSynchronization, debugEnabled, null);
	}


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返回TransactionInfo

	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.
			//记录事务状态
			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.
		//绑定当前线程
		txInfo.bindToThread();
		return txInfo;
	}

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异常回滚

/*
	回滚
	 */
	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);
			}
		//抛出的异常是否是Runtime以及Error类型,可注解自定义异常
			// @Transactional(propagation = Propagation.REQUIRED,rollbackFor = Exception.class)
			if (txInfo.transactionAttribute != null && txInfo.transactionAttribute.rollbackOn(ex)) {
				try {
					//根据TransactionStatus进行回滚
					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 {
					//如果不满足回滚条件,抛出异常也提交
					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;
				}
			}
		}
	}

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	@Override
	public boolean rollbackOn(Throwable ex) {
		if (logger.isTraceEnabled()) {
			logger.trace("Applying rules to determine whether transaction should rollback on " + ex);
		}

		RollbackRuleAttribute winner = null;
		int deepest = Integer.MAX_VALUE;

		//配置的注解@Transactional(propagation = Propagation.REQUIRED,rollbackFor = Exception.class)
		//rollbackFor:封装的属性
		if (this.rollbackRules != null) {
			for (RollbackRuleAttribute rule : this.rollbackRules) {
				int depth = rule.getDepth(ex);
				if (depth >= 0 && depth < deepest) {
					deepest = depth;
					winner = rule;
				}
			}
		}

		if (logger.isTraceEnabled()) {
			logger.trace("Winning rollback rule is: " + winner);
		}

		// User superclass behavior (rollback on unchecked) if no rule matches.
		if (winner == null) {
			logger.trace("No relevant rollback rule found: applying default rules");
			//抛出的异常是RuntimeException,Error判断
			return super.rollbackOn(ex);
		}

		return !(winner instanceof NoRollbackRuleAttribute);
	}
	@Override
	public boolean rollb
	ackOn(Throwable ex) {
		return (ex instanceof RuntimeException || ex instanceof Error);
	}


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	@Override
	public final void rollback(TransactionStatus status) throws TransactionException {
		//如果事务已经完成,再次回滚会异常
		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);
	}


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/*
	有保存点,退回保存点
	没有,如果是新事务,回滚
	如果都不是,多用于JTA,只做回滚标识,提交统一不提交
	清空资源
	 */
	private void processRollback(DefaultTransactionStatus status, boolean unexpected) {
		try {
			boolean unexpectedRollback = unexpected;

			try {
				//激活所有TransactionSynchronization中对应的方法,主要对触发器的调用
				//注册方法:TransactionSynchronizationManager.registerSynchronization
				//在这里基本可以感受到spring强大的扩展性,基本针对每一个点,都做了拦截扩展
				triggerBeforeCompletion(status);

				if (status.hasSavepoint()) {
					if (status.isDebug()) {
						logger.debug("Rolling back transaction to savepoint");
					}
					//如果有保存点,也就是当前事务为单独的线程则会退到保存点
					status.rollbackToHeldSavepoint();
				} else if (status.isNewTransaction()) {
					if (status.isDebug()) {
						logger.debug("Initiating transaction rollback");
					}
					//如果当前事务为独立的新事务,直接回退
					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");
							}
							//当前事务不是独立的事务,则标记状态,等事务链执行完毕后统一回滚
							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) {
				//激活所有TransactionSynchronization中对应的方法
				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 {
			//清空记录的资源并将挂起的资源恢复
			cleanupAfterCompletion(status);
		}
	}

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这个保存点回退,是在嵌套事务的时候建立创建的
在这里插入图片描述

	@Override
	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);
		}
	}

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	@Override
	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);
		}
	}

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	/*
	设置状态
	清除新事务资源
	结束之前挂起
	 */
	private void cleanupAfterCompletion(DefaultTransactionStatus status) {
		//设置完成状态,避免重复调用,抛出异常
		status.setCompleted();
		if (status.isNewSynchronization()) {
			//将绑定当前线程事务信息清除
			TransactionSynchronizationManager.clear();
		}
		if (status.isNewTransaction()) {
			//如果是新事务则清除资源
			doCleanupAfterCompletion(status.getTransaction());
		}
		if (status.getSuspendedResources() != null) {
			if (status.isDebug()) {
				logger.debug("Resuming suspended transaction after completion of inner transaction");
			}
			Object transaction = (status.hasTransaction() ? status.getTransaction() : null);
			//结束之前事务的挂起状态
			resume(transaction, (SuspendedResourcesHolder) status.getSuspendedResources());
		}
	}


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/*
	解除连接绑定
	释放连接
	恢复提交属性
	释放连接
	 */
	protected void doCleanupAfterCompletion(Object transaction) {
		DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;

		// Remove the connection holder from the thread, if exposed.
		if (txObject.isNewConnectionHolder()) {
			//将数据库连接从当前数据库解除绑定
			TransactionSynchronizationManager.unbindResource(obtainDataSource());
		}

		// Reset connection.
		//释放连接
		Connection con = txObject.getConnectionHolder().getConnection();
		try {
			if (txObject.isMustRestoreAutoCommit()) {
				//恢复数据库连接的自动提交属性
				con.setAutoCommit(true);
			}
			//重置数据库连接
			DataSourceUtils.resetConnectionAfterTransaction(con, txObject.getPreviousIsolationLevel());
		}
		catch (Throwable ex) {
			logger.debug("Could not reset JDBC Connection after transaction", ex);
		}

		if (txObject.isNewConnectionHolder()) {
			if (logger.isDebugEnabled()) {
				logger.debug("Releasing JDBC Connection [" + con + "] after transaction");
			}
			//如果当前事务是独立的且新建立的事务则在事务完成时释放数据库连接
			DataSourceUtils.releaseConnection(con, this.dataSource);
		}

		txObject.getConnectionHolder().clear();
	}


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	/*
	当前事务处理结束后,将挂起资源恢复
	 */
	protected final void resume(@Nullable Object transaction, @Nullable SuspendedResourcesHolder resourcesHolder)
			throws TransactionException {

		if (resourcesHolder != null) {
			Object suspendedResources = resourcesHolder.suspendedResources;
			if (suspendedResources != null) {
				//恢复当前事务
				doResume(transaction, suspendedResources);
			}
			List<TransactionSynchronization> suspendedSynchronizations = resourcesHolder.suspendedSynchronizations;
			if (suspendedSynchronizations != null) {
				TransactionSynchronizationManager.setActualTransactionActive(resourcesHolder.wasActive);
				TransactionSynchronizationManager.setCurrentTransactionIsolationLevel(resourcesHolder.isolationLevel);
				TransactionSynchronizationManager.setCurrentTransactionReadOnly(resourcesHolder.readOnly);
				TransactionSynchronizationManager.setCurrentTransactionName(resourcesHolder.name);
				//激活当前线程事务同步,恢复所有给定同步
				doResumeSynchronization(suspendedSynchronizations);
			}
		}
	}

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提交

	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());
		}
	}


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/*
	如果在事务链中已经被标记回滚,执行回滚
	执行提交
	 */
	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;
		//事务异常处理的时候,有一个设置回滚标识的地方
		//如果在事务链中已经被标记回滚,那么直接回滚
		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;
		}

		//处理事务提交
		processCommit(defStatus);
	}

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/*
	有保存点说明是内嵌事务,在每次内嵌事务的时候设置保存点,内嵌事务异常,则回滚.如果没有出现异常,则清除保存点
	保存点清理完成,间接说明不是内嵌事务,则执行.
	也就是说spring利用保存点来间接实现嵌套多层事务的作用
	 */
	private void processCommit(DefaultTransactionStatus status) throws TransactionException {
		try {
			boolean beforeCompletionInvoked = false;

			try {
				boolean unexpectedRollback = false;
				//子类扩展
				prepareForCommit(status);
				//添加TransactionSynchronization中的对应方法调用
				triggerBeforeCommit(status);
				//添加TransactionSynchronization中的对应方法调用
				triggerBeforeCompletion(status);
				beforeCompletionInvoked = true;

				//层层清除内嵌事务，到最后跟事务之后执行提交
				if (status.hasSavepoint()) {
					if (status.isDebug()) {
						logger.debug("Releasing transaction savepoint");
					}
					unexpectedRollback = status.isGlobalRollbackOnly();
					//如果存在保存点信息,则清除
					status.releaseHeldSavepoint();
				} else if (status.isNewTransaction()) {
					if (status.isDebug()) {
						logger.debug("Initiating transaction commit");
					}
					unexpectedRollback = status.isGlobalRollbackOnly();
					//如果是独立的事务,直接提交
					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) {
					//添加TransactionSynchronization中的对应方法调用
					triggerBeforeCompletion(status);
				}
				//出现异常直接回滚
				doRollbackOnCommitException(status, ex);
				throw ex;
			}

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

		} finally {
			cleanupAfterCompletion(status);
		}
	}

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