Spring事务——事务原理源码分析
2023-02-21 本文已影响0人
小波同学
前言
先贴一张从网上找到的Spring事务图，因为源码比较长，结合图看的话，不容易看到后边忘记
以SpringBoot为例，看下SpringBoot是怎么做的。
第一部分：Spring生成事务代理增强类源码分析
一、/META-INF/spring.factories
要想实现某个功能，首先要做的肯定是把bean加载到容器中，Spring通过[spring.factories的方式可以加载一些特定的bean
关于事务的bean请看下图：
TransactionAutoConfiguration、JtaAutoConfiguration
二、TransactionAutoConfiguration
@Configuration
// 类路径下包含PlatformTransactionManager本类生效
@ConditionalOnClass(PlatformTransactionManager.class)
// 在以下四个类本加载后生效
@AutoConfigureAfter({ JtaAutoConfiguration.class, HibernateJpaAutoConfiguration.class,
DataSourceTransactionManagerAutoConfiguration.class,
Neo4jDataAutoConfiguration.class })
// 确保前缀为 spring.transaction 的事务有关属性配置项被加载到 bean TransactionProperties
@EnableConfigurationProperties(TransactionProperties.class)
public class TransactionAutoConfiguration {
@Bean
// 仅在该 bean 不存在时才定义
@ConditionalOnMissingBean
public TransactionManagerCustomizers platformTransactionManagerCustomizers(
ObjectProvider<PlatformTransactionManagerCustomizer<?>> customizers) {
return new TransactionManagerCustomizers(
customizers.orderedStream().collect(Collectors.toList()));
}
@Configuration
// 当能够唯一确定一个PlatformTransactionManager bean时才生效
@ConditionalOnSingleCandidate(PlatformTransactionManager.class)
public static class TransactionTemplateConfiguration {
private final PlatformTransactionManager transactionManager;
public TransactionTemplateConfiguration(
PlatformTransactionManager transactionManager) {
this.transactionManager = transactionManager;
}
@Bean
// 仅在该 bean 不存在时才生效
@ConditionalOnMissingBean
public TransactionTemplate transactionTemplate() {
return new TransactionTemplate(this.transactionManager);
}
}
// 内部类
@Configuration
@ConditionalOnBean(PlatformTransactionManager.class)
@ConditionalOnMissingBean(AbstractTransactionManagementConfiguration.class)
public static class EnableTransactionManagementConfiguration {
@Configuration
// 非常重要的事务注解，下一步要进入这个注解看
// 在属性 spring.aop.proxy-target-class 被明确设置为 false 时启用注解
@EnableTransactionManagement(proxyTargetClass = false)
@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "false", matchIfMissing = false)
public static class JdkDynamicAutoProxyConfiguration {
}
@Configuration
// 非常重要的事务注解，下一步要进入这个注解看
// 在属性 spring.aop.proxy-target-class 缺失或者被明确设置为 true 时启用注解
@EnableTransactionManagement(proxyTargetClass = true)
// matchIfMissing 为true，因为默认是没有配置的，所以spring默认走的是cglib代理
@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "true", matchIfMissing = true)
public static class CglibAutoProxyConfiguration {
}
}
}
三、@EnableTransactionManagement
到这里我们第一个问题已经有答案了，AdviceMode 默认使用的是PROXY，同一个类中方法调用，拦截器不会生效，所以我们在同一类中即使调用一个事务方法，方法拦截器不会生效，事务就不会生效。
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import({TransactionManagementConfigurationSelector.class})
public @interface EnableTransactionManagement {
// proxyTargetClass = false表示是JDK动态代理支持接口代理。true表示是Cglib代理支持子类继承代理。
boolean proxyTargetClass() default false;
// 事务通知模式(切面织入方式)，默认代理模式（同一个类中方法互相调用拦截器不会生效），可以选择增强型AspectJ
AdviceMode mode() default AdviceMode.PROXY;
// 连接点上有多个通知时，排序，默认最低。值越大优先级越低。
int order() default 2147483647;
}
这里通过@Import导入了TransactionManagementConfigurationSelector类
四、TransactionManagementConfigurationSelector
如上图所示，TransactionManagementConfigurationSelector继承自AdviceModeImportSelector实现了ImportSelector接口
- 给容器中注册一个 InfrastructureAdvisorAutoProxyCreator 组件；利用后置处理器机制在对象创建以后，包装对象，返回一个代理对象（增强器），代理对象执行方法利用拦截器链进行调用；
- ProxyTransactionManagementConfiguration：就是一个配置类，定义了事务增强器。
public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> {
public TransactionManagementConfigurationSelector() {
}
protected String[] selectImports(AdviceMode adviceMode) {
switch(adviceMode) {
// 默认会走这里，载入了AutoProxyRegistrar、ProxyTransactionManagementConfiguration2个类
case PROXY:
return new String[]{AutoProxyRegistrar.class.getName(), ProxyTransactionManagementConfiguration.class.getName()};
case ASPECTJ:
return new String[]{this.determineTransactionAspectClass()};
default:
return null;
}
}
//。。。。。。
}
4.1、AutoProxyRegistrar
实现了ImportBeanDefinitionRegistrar接口，重写registerBeanDefinitions方法，源码如下：
最终调用的是：registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);源码自己看下，因为关联关系不大，就不展开了，这个方法的目的是注册InfrastructureAdvisorAutoProxyCreator的BeanDefinitio
public class AutoProxyRegistrar implements ImportBeanDefinitionRegistrar {
private final Log logger = LogFactory.getLog(getClass());
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
boolean candidateFound = false;
Set<String> annTypes = importingClassMetadata.getAnnotationTypes();
for (String annType : annTypes) {
AnnotationAttributes candidate = AnnotationConfigUtils.attributesFor(importingClassMetadata, annType);
if (candidate == null) {
continue;
}
Object mode = candidate.get("mode");
Object proxyTargetClass = candidate.get("proxyTargetClass");
if (mode != null && proxyTargetClass != null && AdviceMode.class == mode.getClass() &&
Boolean.class == proxyTargetClass.getClass()) {
candidateFound = true;
// 默认代理模式，进入到这个方法
if (mode == AdviceMode.PROXY) {
// 最终调用的是：registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);基础构建增强自动代理构造器
AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
if ((Boolean) proxyTargetClass) {
AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
return;
}
}
}
}
if (!candidateFound && logger.isInfoEnabled()) {
String name = getClass().getSimpleName();
}
}
}
4.2、InfrastructureAdvisorAutoProxyCreator
Infrastructure：基础设施
看下类继承结构，这里需要首先了解下Spring容器的加载过程，了解BeanPostProcessor接口的作用
因为间接实现了InstantiationAwareBeanPostProcessor，AbstractAutoProxyCreator（InfrastructureAdvisorAutoProxyCreator继承了它）重写了接口两个方法，对bean进行了一些操作：
- postProcessBeforeInstantiation：实例化前
- postProcessAfterInitialization：初始化后
4.3、AbstractAutoProxyCreator
public abstract class AbstractAutoProxyCreator extends ProxyProcessorSupport
implements SmartInstantiationAwareBeanPostProcessor, BeanFactoryAware {
/**
* 在创建Bean的流程中还没调用构造器来实例化Bean的时候进行调用(实例化前后)
* AOP解析切面以及事务解析事务注解都是在这里完成的
*/
@Override
public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) {
//获取BeanClass的缓存key
Object cacheKey = getCacheKey(beanClass, beanName);
if (!StringUtils.hasLength(beanName) || !this.targetSourcedBeans.contains(beanName)) {
//advisedBeans保存了所有已经做过动态代理的Bean
// 如果被解析过则直接返回
if (this.advisedBeans.containsKey(cacheKey)) {
return null;
}
// 1. 判断当前bean是否是基础类型：是否实现了Advice，Pointcut，Advisor，AopInfrastructureBean这些接口或是否是切面(@Aspect注解)
// 2. 判断是不是应该跳过 (AOP解析直接解析出我们的切面信息，
// 而事务在这里是不会解析的)
if (isInfrastructureClass(beanClass) || shouldSkip(beanClass, beanName)) {
//添加进advisedBeans ConcurrentHashMap<k=Object,v=Boolean>标记是否需要增强实现，
// 这里基础构建bean不需要代理，都置为false，供后面postProcessAfterInitialization实例化后使用。
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return null;
}
}
//获取用户自定义的targetSource, 如果存在则直接在对象实例化之前进行代理创建,
// 避免了目标对象不必要的实例化
TargetSource targetSource = getCustomTargetSource(beanClass, beanName);
//如果有自定义targetSource就要这里创建代理对象
//这样做的好处是被代理的对象可以动态改变，而不是值针对一个target对象(可以对对象池中对象进行代理，可以每次创建代理都创建新对象
if (targetSource != null) {
if (StringUtils.hasLength(beanName)) {
this.targetSourcedBeans.add(beanName);
}
//获取Advisors, 这个是交给子类实现的
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(beanClass, beanName, targetSource);
Object proxy = createProxy(beanClass, beanName, specificInterceptors, targetSource);
this.proxyTypes.put(cacheKey, proxy.getClass());
//返回代理的对象
return proxy;
}
return null;
}
@Override
public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
if (bean != null) {
Object cacheKey = getCacheKey(bean.getClass(), beanName);
//当 Bean 被循环引用, 并且被暴露了,
// 则会通过 getEarlyBeanReference 来创建代理类;
// 通过判断 earlyProxyReferences 中
// 是否存在 beanName 来决定是否需要对 target 进行动态代理
if (this.earlyProxyReferences.remove(cacheKey) != bean) {
//该方法将会返回代理类
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}
/**
* Spring实现Bean代理的核心方法。wrapIfNecessary在两处会被调用，一处是getEarlyBeanReference，
* 另一处是postProcessAfterInitialization
*/
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
//已经被处理过
// 1.判断当前bean是否在targetSourcedBeans缓存中存在（已经处理过），如果存在，则直接返回当前bean
if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
return bean;
}
//不需要被织入逻辑的
// 2.在advisedBeans缓存中存在，并且value为false，则代表无需处理
if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
return bean;
}
//是不是基础的bean 是不是需要跳过的
// 3.bean的类是aop基础设施类 || bean应该跳过，则标记为无需处理，并返回
if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
// Create proxy if we have advice.
// 返回匹配当前Bean的所有Advice\Advisor\Interceptor
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
// 5.如果存在增强器则创建代理
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
//创建Bean对应的代理，SingletonTargetSource用于封装实现类的信息
// 5.1 创建代理对象：这边SingletonTargetSource的target属性存放的就是我们原来的bean实例（也就是被代理对象），
// 用于最后增加逻辑执行完毕后，通过反射执行我们真正的方法时使用（method.invoke(bean, args)）
Object proxy = createProxy(
bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
// 5.2 创建完代理后，将cacheKey -> 代理类的class放到缓存
this.proxyTypes.put(cacheKey, proxy.getClass());
// 返回代理对象
return proxy;
}
//该Bean是不需要进行代理的，下次就不需要重复生成了
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
}
4.4 createProxy
public abstract class AbstractAutoProxyCreator extends ProxyProcessorSupport
implements SmartInstantiationAwareBeanPostProcessor, BeanFactoryAware {
protected Object createProxy(Class<?> beanClass, @Nullable String beanName,
@Nullable Object[] specificInterceptors, TargetSource targetSource) {
//如果beanFactory是ConfigurableListableBeanFactory的类型，暴露目标类
if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
}
//创建一个ProxyFactory，当前ProxyCreator在创建代理时将需要用到的字段赋值到ProxyFactory中去
ProxyFactory proxyFactory = new ProxyFactory();
//将 当前的AnnotationAwareAspectJAutoProxyCreator 对象的属性赋值给ProxyFactory对象
proxyFactory.copyFrom(this);
// 处理 proxyTargetClass 属性
// 如果希望使用 CGLIB 来代理接口，可以配置
// proxy-target-class="true",这样不管有没有接口，都使用 CGLIB 来生成代理：
// <aop:config proxy-target-class="true"></aop:config>
if (!proxyFactory.isProxyTargetClass()) {
// 检查preserveTargetClass属性，判断beanClass是应该基于类代理还是基于接口代理
if (shouldProxyTargetClass(beanClass, beanName)) {
// 如果是基于类代理，则将proxyTargetClass赋值为true
proxyFactory.setProxyTargetClass(true);
}
else {
// 评估bean的代理接口
// 1. 有接口的，调用一次或多次：proxyFactory.addInterface(ifc);
// 2. 没有接口的，调用：proxyFactory.setProxyTargetClass(true);
evaluateProxyInterfaces(beanClass, proxyFactory);
}
}
// 这个方法主要来对前面传递进来的横切逻辑实例进行包装
// 注意：如果 specificInterceptors 中有 Advice 和 Interceptor，它们也会被包装成 Advisor
// 方法会整理合并得到最终的advisors （毕竟interceptorNames还指定了一些拦截器的）
// 至于调用的先后顺序，通过方法里的applyCommonInterceptorsFirst参数可以进行设置，
// 若applyCommonInterceptorsFirst为true，interceptorNames属性指定的Advisor优先调用。默认为true
Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
// 将advisors添加到proxyFactory
proxyFactory.addAdvisors(advisors);
// 设置要代理的类，将targetSource赋值给proxyFactory的targetSource属性，之后可以通过该属性拿到被代理的bean的实例
proxyFactory.setTargetSource(targetSource);
// 这个方法是交给子类的，子类可以继续去定制此proxyFactory
customizeProxyFactory(proxyFactory);
// 用来控制proxyFactory被配置之后，是否还允许修改通知。默认值为false（即在代理被配置之后，不允许修改代理类的配置）
proxyFactory.setFrozen(this.freezeProxy);
// 设置preFiltered的属性值，默认是false。子类：AbstractAdvisorAutoProxyCreator修改为true
// preFiltered字段意思为：是否已为特定目标类筛选Advisor
// 这个字段和DefaultAdvisorChainFactory.getInterceptorsAndDynamicInterceptionAdvice获取所有的Advisor有关
//CglibAopProxy和JdkDynamicAopProxy都会调用此方法，然后递归执行所有的Advisor
if (advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}
// 使用proxyFactory获取代理
return proxyFactory.getProxy(getProxyClassLoader());
}
}
五、看到这里，大家可能对createProxy 有些疑问，我们还没有定义Advisor呀，Advisor是哪来的？
我们再回到第四步看一下，之前4.1、4.2、4.3、4.4看的全都是AutoProxyRegistrar源码，下边分析下ProxyTransactionManagementConfiguration是干嘛的。
第一个方法就是定义事务增强器的，返回的BeanFactoryTransactionAttributeSourceAdvisor对象其实是间接实现了Advisor接口的，大家可以看下类图。
最终，加载了一个事务的Advisor，这个里边配置了Advice：TransactionInterceptor，真正方法执行时会拦截到。
注意：BeanFactoryTransactionAttributeSourceAdvisor实现的是PointcutAdvisor接口，既可以设置Advice，又可以设置Pointcut。
但是下面代码中只配置了Adice，而pointcut是由BeanFactoryTransactionAttributeSourceAdvisor类完成的配置。
@Configuration
public class ProxyTransactionManagementConfiguration extends AbstractTransactionManagementConfiguration {
public ProxyTransactionManagementConfiguration() {
}
/**
* 定义事务增强器 注册了Advisor
*/
@Bean(
name = {"org.springframework.transaction.config.internalTransactionAdvisor"}
)
//声明的role为基础类（Spring内部使用的类）
//int ROLE_INFRASTRUCTURE = 2;
@Role(2)
public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor() {
BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();
advisor.setTransactionAttributeSource(this.transactionAttributeSource());
//配置Advice
// 这里的定义了事务拦截器
advisor.setAdvice(this.transactionInterceptor());
if (this.enableTx != null) {
advisor.setOrder((Integer)this.enableTx.getNumber("order"));
}
return advisor;
}
/**
* 定义基于注解的事务属性资源
*/
@Bean
@Role(2)
public TransactionAttributeSource transactionAttributeSource() {
return new AnnotationTransactionAttributeSource();
}
/**
* 定义事务拦截器 注册了Advice
*/
@Bean
@Role(2)
public TransactionInterceptor transactionInterceptor() {
TransactionInterceptor interceptor = new TransactionInterceptor();
interceptor.setTransactionAttributeSource(this.transactionAttributeSource());
if (this.txManager != null) {
interceptor.setTransactionManager(this.txManager);
}
return interceptor;
}
}
public class BeanFactoryTransactionAttributeSourceAdvisor extends AbstractBeanFactoryPointcutAdvisor {
@Nullable
private TransactionAttributeSource transactionAttributeSource;
//pointcut 是TransactionAttributeSourcePointcut 的子类，实现了TransactionAttributeSource 方法。
//该方法的作用，是用户可以配置`解析器`。
private final TransactionAttributeSourcePointcut pointcut = new TransactionAttributeSourcePointcut() {
@Override
@Nullable
protected TransactionAttributeSource getTransactionAttributeSource() {
return transactionAttributeSource;
}
};
public void setTransactionAttributeSource(TransactionAttributeSource transactionAttributeSource) {
this.transactionAttributeSource = transactionAttributeSource;
}
@Override
public Pointcut getPointcut() {
return this.pointcut;
}
}
六、Spring解析事务注解
6.1 方法匹配
如何判断bean方法符合规则？判断是否能获取事务属性对象。
自动代理器会遍历bean的所有方法，判断是否与MethodMatcher匹配。实际上会调用TransactionAttributeSourcePointcut的matches方法。
abstract class TransactionAttributeSourcePointcut extends StaticMethodMatcherPointcut implements Serializable {
@Override
public boolean matches(Method method, Class<?> targetClass) {
if (TransactionalProxy.class.isAssignableFrom(targetClass) ||
PlatformTransactionManager.class.isAssignableFrom(targetClass) ||
PersistenceExceptionTranslator.class.isAssignableFrom(targetClass)) {
return false;
}
//若TransactionAttributeSource 对象不为空，那么获取方法上的事务属性对象。
TransactionAttributeSource tas = getTransactionAttributeSource();
return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
}
/**
* 抽象方法，但是注册的Advisor中的pointcut是TransactionAttributeSourcePointcut 子类。
* 实际上获取的是TransactionAttributeSource 对象
*/
@Nullable
protected abstract TransactionAttributeSource getTransactionAttributeSource();
}
6.2 事务属性获取
解析事务注解，获取事务属性对象。
实际上TransactionAttributeSource为3.1配置的AnnotationTransactionAttributeSource对象。
当然这个类实现的只是特有的方法，而算法骨干由其父类AbstractFallbackTransactionAttributeSource实现。
注意getTransactionAttribute方法返回null，则证明pointcut不匹配bean的某方法。
public abstract class AbstractFallbackTransactionAttributeSource implements TransactionAttributeSource {
@Override
@Nullable
public TransactionAttribute getTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
//若是Object的方法，直接返回null
if (method.getDeclaringClass() == Object.class) {
return null;
}
// 首先看缓存是否存在
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 {
//获取TransactionAttribute 对象的核心方法（如下所示）
TransactionAttribute txAttr = computeTransactionAttribute(method, targetClass);
//填充缓存
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;
}
}
@Nullable
protected TransactionAttribute computeTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
// 该方法是否要求必须是public级别（因为自动代理会对所有方法进行代匹配）
if (allowPublicMethodsOnly() && !Modifier.isPublic(method.getModifiers())) {
return null;
}
//获取明确类的方法（处理桥接方法）
Method specificMethod = AopUtils.getMostSpecificMethod(method, targetClass);
//由子类实现（获取方法上的事务配置）
TransactionAttribute txAttr = findTransactionAttribute(specificMethod);
if (txAttr != null) {
return txAttr;
}
//由子类实现（获取类上的事务配置）
txAttr = findTransactionAttribute(specificMethod.getDeclaringClass());
if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {
return txAttr;
}
//获取原始方法上的事务配置
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;
}
}
下图的两个抽象方法，由子类实现。
还需要注意的一个细节，AnnotationTransactionAttributeSource是其唯一子类。
public class AnnotationTransactionAttributeSource extends AbstractFallbackTransactionAttributeSource
implements Serializable {
private final Set<TransactionAnnotationParser> annotationParsers;
public AnnotationTransactionAttributeSource(boolean publicMethodsOnly) {
this.publicMethodsOnly = publicMethodsOnly;
if (jta12Present || ejb3Present) {
this.annotationParsers = new LinkedHashSet<>(4);
this.annotationParsers.add(new SpringTransactionAnnotationParser());
if (jta12Present) {
this.annotationParsers.add(new JtaTransactionAnnotationParser());
}
if (ejb3Present) {
this.annotationParsers.add(new Ejb3TransactionAnnotationParser());
}
}
else {
//通用模式下，为SpringTransactionAnnotationParser解析器
this.annotationParsers = Collections.singleton(new SpringTransactionAnnotationParser());
}
}
@Override
@Nullable
protected TransactionAttribute findTransactionAttribute(Class<?> clazz) {
return determineTransactionAttribute(clazz);
}
@Override
@Nullable
protected TransactionAttribute findTransactionAttribute(Method method) {
return determineTransactionAttribute(method);
}
//遍历解析器，获取事务注解
@Nullable
protected TransactionAttribute determineTransactionAttribute(AnnotatedElement element) {
for (TransactionAnnotationParser annotationParser : this.annotationParsers) {
TransactionAttribute attr = annotationParser.parseTransactionAnnotation(element);
if (attr != null) {
return attr;
}
}
return null;
}
}
parseTransactionAnnotation()方法，遍历方法/类上的事务注解。获取到TransactionAttribute对象。
public class SpringTransactionAnnotationParser implements TransactionAnnotationParser, Serializable {
@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;
}
}
}
若MethodMatcher返回true，则证明该方法可以被事务增强器去增强。将Advisor加入到List中，并开始处理下一个Advisor。最终获取到所有可切入的Advisor。去创建代理对象。
总结
- 1、SpringBoot通过spring.factories文件引入TransactionAutoConfiguration类
- 2、TransactionAutoConfiguration默认设置CglibAutoProxyConfiguration 做代理，开启了@EnableTransactionManagement注解
- 3、@EnableTransactionManagement注解引入了TransactionManagementConfigurationSelector类
- 4、TransactionManagementConfigurationSelector加载了：
- AutoProxyRegistrar:用于注册自动代理生成器（InfrastructureAdvisorAutoProxyCreator）
- ProxyTransactionManagementConfiguration：配置引入了事务的增强器
- 5、在Spring初始化的时候，InfrastructureAdvisorAutoProxyCreator在bean的实例化前和初始化后，执行生成事务增强代理的逻辑，生成事务增强器
- 6、配置了Advice：TransactionInterceptor，真正方法执行时会拦截到
第二部分：Spring 事务执行
上面讲到 TransactionManagementConfigurationSelector加载了ProxyTransactionManagementConfiguration，里边注册了一个bean：TransactionInterceptor，实现了MethodInterceptor（Spring方法拦截器），事务就是在这个类中进行处理的，首先看一下类图
因为实现了MethodInterceptor，看下invoke()方法，方法拦截的核心代码。
一、invoke()
调用了父类TransactionAspectSupport的invokeWithinTransaction()方法
invokeWithinTransaction方法的大致流程是这样的：
- 获取要被代理的方法绑定的事务属性TransactionAttribute，属性不为空或者是非回调偏向的事务管理器，开始进行声明式事务；
- determineTransactionManager方法获取PlatformTransactionManager；
- createTransactionIfNecessary方法创建TransactionInfo（开启事务）；
- 执行 retVal = invocation.proceedWithInvocation();
- catch抛出异常是判断事务是否需要回滚
- finally 清除当前事务信息
- 最终提交事务
public class TransactionInterceptor extends TransactionAspectSupport implements MethodInterceptor, Serializable {
@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...
// 调用TransactionAspectSupport的 invokeWithinTransaction方法
return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);
}
}
public abstract class TransactionAspectSupport implements BeanFactoryAware, InitializingBean {
@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();
// 如果transaction attribute为空,该方法就是非事务（非编程式事务）
final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
final PlatformTransactionManager tm = determineTransactionManager(txAttr);
final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);
// 标准声明式事务：如果事务属性为空 或者 非回调偏向的事务管理器
if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
// Standard transaction demarcation with getTransaction and commit/rollback calls.
TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
Object retVal;
try {
// 这里就是一个环绕增强，在这个proceed前后可以自己定义增强实现
// 实现类 ReflectiveMethodInvocation
retVal = invocation.proceedWithInvocation();
}
catch (Throwable ex) {
// 根据事务定义的，该异常需要回滚就回滚，否则提交事务
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
}
finally {
//清空当前事务信息，重置为老的
cleanupTransactionInfo(txInfo);
}
//返回结果之前提交事务
commitTransactionAfterReturning(txInfo);
return retVal;
}
// 从此往下是编程式事务，暂时不做了解
else {
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;
}
}
}
}
总结
到此，Spring事务的流程就完了，上边提到的几个方法感兴趣的可以去翻一下源码
第三部分：PlatformTransactionManager
四、PlatformTransactionManager
jdbc主要用到的管理器是DataSourceTransactionManager，实现了PlatformTransactionManager，分析一下三个方法。
public interface PlatformTransactionManager {
// 获取事务状态
TransactionStatus getTransaction(@Nullable TransactionDefinition definition)
throws TransactionException;
// 提交
void commit(TransactionStatus status) throws TransactionException;
// 回滚
void rollback(TransactionStatus status) throws TransactionException;
}
五、getTransaction获取事务
Spring事务的传播行为实现就在这里，上图。
public abstract class AbstractPlatformTransactionManager implements PlatformTransactionManager, Serializable {
@Override
public final TransactionStatus getTransaction(@Nullable TransactionDefinition definition) throws TransactionException {
Object transaction = doGetTransaction();
boolean debugEnabled = logger.isDebugEnabled();
if (definition == null) {
// 事务属性为空，使用默认的属性
definition = new DefaultTransactionDefinition();
}
// 如果当前已经存在事务
if (isExistingTransaction(transaction)) {
// Existing transaction found -> check propagation behavior to find out how to behave.
// 根据不同传播机制不同处理
return handleExistingTransaction(definition, transaction, debugEnabled);
}
// 超时不能小于默认值
// Check definition settings for new transaction.
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.
// 当前不存在事务，传播机制=MANDATORY（支持当前事务，没事务报错），报错
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_MANDATORY) {
throw new IllegalTransactionStateException(
"No existing transaction found for transaction marked with propagation 'mandatory'");
}
// 当前不存在事务，传播机制=REQUIRED/REQUIRED_NEW/NESTED,这三种情况，需要新开启事务，且加上事务同步
else if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRED ||
definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW ||
definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
SuspendedResourcesHolder suspendedResources = suspend(null);
if (debugEnabled) {
logger.debug("Creating new transaction with name [" + definition.getName() + "]: " + definition);
}
try {
// 是否需要开启同步
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
DefaultTransactionStatus status = newTransactionStatus(
definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
// 开启新事务
doBegin(transaction, definition);
//准备同步
prepareSynchronization(status, definition);
return status;
}
catch (RuntimeException | Error ex) {
resume(null, suspendedResources);
throw ex;
}
}
else {
// Create "empty" transaction: no actual transaction, but potentially synchronization.
// 当前不存在事务当前不存在事务，且传播机制=PROPAGATION_SUPPORTS/PROPAGATION_NOT_SUPPORTED/PROPAGATION_NEVER，这三种情况，
// 创建“空”事务:没有实际事务，但可能是同步。
// 警告：定义了隔离级别，但并没有真实的事务初始化，
// 隔离级别被忽略有隔离级别但是并没有定义实际的事务初始化，有隔离级别但是并没有定义实际的事务初始化，
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);
}
}
}
这里分成了两部分：
- 当前已存在事务：isExistingTransaction()判断是否存在事务，存在事务handleExistingTransaction()根据不同传播机制不同处理
- 当前不存在事务：不同传播机制不同处理
handleExistingTransaction()源码如下：
public abstract class AbstractPlatformTransactionManager implements PlatformTransactionManager, Serializable {
/**
* Create a TransactionStatus for an existing transaction.
*/
private TransactionStatus handleExistingTransaction(
TransactionDefinition definition, Object transaction, boolean debugEnabled)
throws TransactionException {
// 1.NERVER（不支持当前事务;如果当前事务存在，抛出异常）报错
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NEVER) {
throw new IllegalTransactionStateException(
"Existing transaction found for transaction marked with propagation 'never'");
}
// 2.NOT_SUPPORTED（不支持当前事务，现有同步将被挂起）挂起当前事务
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);
}
// 3.REQUIRES_NEW挂起当前事务，创建新事务
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW) {
if (debugEnabled) {
logger.debug("Suspending current transaction, creating new transaction with name [" +
definition.getName() + "]");
}
// 挂起当前事务
SuspendedResourcesHolder suspendedResources = suspend(transaction);
try {
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;
}
}
// 4.NESTED嵌套事务
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() + "]");
}
// 是否支持保存点：非JTA事务走这个分支。
// AbstractPlatformTransactionManager默认是true，
// JtaTransactionManager复写了该方法false，
// DataSourceTransactionmanager没有复写，
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.
DefaultTransactionStatus status =
prepareTransactionStatus(definition, transaction, false, false, debugEnabled, null);
// 创建保存点
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.
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");
}
if (isValidateExistingTransaction()) {
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)"));
}
}
if (!definition.isReadOnly()) {
if (TransactionSynchronizationManager.isCurrentTransactionReadOnly()) {
throw new IllegalTransactionStateException("Participating transaction with definition [" +
definition + "] is not marked as read-only but existing transaction is");
}
}
}
// 到这里PROPAGATION_SUPPORTS 或 PROPAGATION_REQUIRED或PROPAGATION_MANDATORY，
// 存在事务加入事务即可，prepareTransactionStatus第三个参数就是是否需要新事务。false代表不需要新事务
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
return prepareTransactionStatus(definition, transaction, false, newSynchronization, debugEnabled, null);
}
}
这里有两个核心方法
-
suspend()：
- 把当前事务的connectionHolder数据库连接持有者清空；
- 当前线程解绑datasource.其实就是ThreadLocal移除对应变量（TransactionSynchronizationManager类中定义的private static final ThreadLocal<Map<Object, Object>> resources = new NamedThreadLocal<Map<Object, Object>>("Transactional resources");）
-
doBegin()
参考：
https://blog.csdn.net/StringBuff/article/details/111812282
