【原创】002 | 搭上SpringBoot事务源码分析专车

前言

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专车介绍**

该趟专车是开往Spring Boot事务源码分析的专车

专车问题

• 为什么加上@Transactional注解就可以实现事务？
• 分析事务源码之后我们可以学到什么？

专车名词

事务

程序中通常使用事务来达到数据的一致性，从而避免脏数据

编程式事务

在业务方法开头开启事务，然后对我们的业务进行try-catch，假设没有异常则提交事务，如果出现异常，则在catch模块回滚事务

声明式事务由来

如果采用编程式事务，那么在任何需要事务的地方都要开启事务、try-catch、提交或者回滚事务，会导致重复编码、编写与业务无关的代码。基于Spring Aop思想，我们可以利用Aop的方式，对需要使用事务的方法进行增强，将公用的部分提取出来，那么就实现了声明式事务。

Spring提供的声明式事务

在需要使用事务的业务方法上添加@Transactional注解，那么就可以使用事务的特性，要么成功，要么失败

Spring Aop核心概念

• 切面：切面是由切点和通知组成
• 切点：用来匹配符合条件类或方法
• 通知：需要执行的操作

专车分析

基于Spring Boot自动配置原理，我们应该寻找xxxAutoConfiguration自动配置类，此处要寻找和事务相关的，那么自然是TransactionAutoConfiguration

自动配置

打开TransactionAutoConfiguration自动配置类

@Configuration
@ConditionalOnBean(PlatformTransactionManager.class)
@ConditionalOnMissingBean(AbstractTransactionManagementConfiguration.class)
public static class EnableTransactionManagementConfiguration {@Configuration
@EnableTransactionManagement(proxyTargetClass = false)
@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "false", matchIfMissing = false)
public static class JdkDynamicAutoProxyConfiguration {}@Configuration
@EnableTransactionManagement(proxyTargetClass = true)
@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "true", matchIfMissing = true)
public static class CglibAutoProxyConfiguration {}}


可以看到开启事务管理器的注解@EnableTransactionManagement

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(TransactionManagementConfigurationSelector.class)
public @interface EnableTransactionManagement {}


查看TransactionManagementConfigurationSelector导入的类

protected String[] selectImports(AdviceMode adviceMode) {
switch (adviceMode) {
case PROXY:
return new String[] {AutoProxyRegistrar.class.getName(),
ProxyTransactionManagementConfiguration.class.getName()};
case ASPECTJ:
return new String[] {determineTransactionAspectClass()};
default:
return null;
}
}


可以看到导入了AutoProxyRegistrar和ProxyTransactionManagementConfiguration

首先看看AutoProxyRegistrar，该类实现了ImportBeanDefinitionRegistrar

public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
boolean candidateFound = false;
Set<String> annoTypes = importingClassMetadata.getAnnotationTypes();
for (String annoType : annoTypes) {
AnnotationAttributes candidate = AnnotationConfigUtils.attributesFor(importingClassMetadata, annoType);
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;
if (mode == AdviceMode.PROXY) {
// 注册自动代理创建器
AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
if ((Boolean) proxyTargetClass) {
AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
return;
}
}
}
}
}


注册自动代理创建器，AopConfigUtils#registerAutoProxyCreatorIfNecessary

public static BeanDefinition registerAutoProxyCreatorIfNecessary(
BeanDefinitionRegistry registry, @Nullable Object source) {
// 注册了InfrastructureAdvisorAutoProxyCreator到IOC容器中
return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
}


InfrastructureAdvisorAutoProxyCreator是AbstractAutoProxyCreator的子类，AbstractAutoProxyCreator又实现了BeanPostProcessor接口，那么在bean初始化完毕后就会调用postProcessAfterInstantiation()方法，postProcessAfterInstantiation()定义在AbstractAutoProxyCreator类中

BeanPostProcessor后置处理

打开AbstractAutoProxyCreator

@Override
public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
if (bean != null) {
Object cacheKey = getCacheKey(bean.getClass(), beanName);
if (!this.earlyProxyReferences.contains(cacheKey)) {
// 如果满足条件对bean进行包裹
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}


该方法调用了wrapIfNecessary()方法

protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
// Create proxy if we have advice.
// 获取bean的切面和通知
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
// 需要代理
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;
}


根据注释的意思就是如果存在advice，那么就创建代理，

寻找切面

进入AbstractAdvisorAutoProxyCreator#getAdvicesAndAdvisorsForBean

protected Object[] getAdvicesAndAdvisorsForBean(
Class<?> beanClass, String beanName, @Nullable TargetSource targetSource) {
// 查找符合条件的切面
List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
// 不存在符合条件的切面，则不生成代理
if (advisors.isEmpty()) {
return DO_NOT_PROXY;
}
return advisors.toArray();
}


该代码第一句最重要，如果不存在符合条件的切面，那么最终的结果返回null，根据上面分析的，如果为null就不创建代理，否则创建代理。接下来看看第一句的实现

protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
// 获取所有候选的切面，也就是类型为Advisor的切面，此处获取到的候选切面为BeanFactoryTransactionAttributeSourceAdvisor
List<Advisor> candidateAdvisors = findCandidateAdvisors();
// 从候选的切面中获取可以解析当前bean的切面，最终符合条件的切面为BeanFactoryTransactionAttributeSourceAdvisor
List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
extendAdvisors(eligibleAdvisors);
if (!eligibleAdvisors.isEmpty()) {
eligibleAdvisors = sortAdvisors(eligibleAdvisors);
}
return eligibleAdvisors;
}

为什么上面获取到的切面是BeanFactoryTransactionAttributeSourceAdvisor？是否还记得之前导入配置类的时候还有一个配置类没有分析？那就是ProxyTransactionManagementConfiguration

打开ProxyTransactionManagementConfiguration

@Configuration
public class ProxyTransactionManagementConfiguration extends AbstractTransactionManagementConfiguration { // 创建BeanFactoryTransactionAttributeSourceAdvisor
@Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor() {
BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();
advisor.setTransactionAttributeSource(transactionAttributeSource());
// 设置切面对应的通知，后面分析会用到
advisor.setAdvice(transactionInterceptor());
if (this.enableTx != null) {
advisor.setOrder(this.enableTx.<Integer>getNumber("order"));
}
return advisor;
}@Bean
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public TransactionAttributeSource transactionAttributeSource() {
return new AnnotationTransactionAttributeSource();
} // 创建通知
@Bean
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public TransactionInterceptor transactionInterceptor() {
TransactionInterceptor interceptor = new TransactionInterceptor();
interceptor.setTransactionAttributeSource(transactionAttributeSource());
if (this.txManager != null) {
interceptor.setTransactionManager(this.txManager);
}
return interceptor;
}}

通过上面的自动配置，可得知获取到的候选切面为什么是BeanFactoryTransactionAttributeSourceAdvisor

接下来看看如何从候选切面中找到可以解析当前bean的切面？

protected List<Advisor> findAdvisorsThatCanApply(
List<Advisor> candidateAdvisors, Class<?> beanClass, String beanName) {ProxyCreationContext.setCurrentProxiedBeanName(beanName);
try {
// 查找可以解析当前bean对应的切面
return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
}
finally {
ProxyCreationContext.setCurrentProxiedBeanName(null);
}
}

查找可以解析当前bean对应的切面，AopUtils#findAdvisorsThatCanApply

public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) {
if (candidateAdvisors.isEmpty()) {
return candidateAdvisors;
}
List<Advisor> eligibleAdvisors = new ArrayList<>();
for (Advisor candidate : candidateAdvisors) {
if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {
eligibleAdvisors.add(candidate);
}
}
boolean hasIntroductions = !eligibleAdvisors.isEmpty();
for (Advisor candidate : candidateAdvisors) {
if (candidate instanceof IntroductionAdvisor) {
// already processed
continue;
}
// 当前切面是否可以解析bean
if (canApply(candidate, clazz, hasIntroductions)) {
eligibleAdvisors.add(candidate);
}
}
return eligibleAdvisors;
}

候选切面是否可以解析bean

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) {
// 由上面分析知道最终的候选切面为BeanFactoryTransactionAttributeSourceAdvisor
// 该类实现了PointcutAdvisor
PointcutAdvisor pca = (PointcutAdvisor) advisor;
return canApply(pca.getPointcut(), targetClass, hasIntroductions);
}
else {
// It doesn't have a pointcut so we assume it applies.
return true;
}
}

候选切面是否可以解析bean

public static boolean canApply(Pointcut pc, Class<?> targetClass, boolean hasIntroductions) {
Assert.notNull(pc, "Pointcut must not be null");
if (!pc.getClassFilter().matches(targetClass)) {
return false;
} // 获取切面切点方法匹配对象，用来匹配方法是否符合
MethodMatcher methodMatcher = pc.getMethodMatcher();
if (methodMatcher == MethodMatcher.TRUE) {
// No need to iterate the methods if we're matching any method anyway...
return true;
}IntroductionAwareMethodMatcher introductionAwareMethodMatcher = null;
if (methodMatcher instanceof IntroductionAwareMethodMatcher) {
introductionAwareMethodMatcher = (IntroductionAwareMethodMatcher) methodMatcher;
}Set<Class<?>> classes = new LinkedHashSet<>();
if (!Proxy.isProxyClass(targetClass)) {
classes.add(ClassUtils.getUserClass(targetClass));
}
classes.addAll(ClassUtils.getAllInterfacesForClassAsSet(targetClass));for (Class<?> clazz : classes) {
// 通过反射获取当前类所有的Method对象
Method[] methods = ReflectionUtils.getAllDeclaredMethods(clazz);
for (Method method : methods) {
if (introductionAwareMethodMatcher != null ?
introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions) :
// 匹配方法是否符合
methodMatcher.matches(method, targetClass)) {
return true;
}
}
}return false;
}

匹配方法TransactionAttributeSourcePointcut#matches

public boolean matches(Method method, Class<?> targetClass) {
if (TransactionalProxy.class.isAssignableFrom(targetClass) ||
PlatformTransactionManager.class.isAssignableFrom(targetClass) ||
PersistenceExceptionTranslator.class.isAssignableFrom(targetClass)) {
return false;
}
TransactionAttributeSource tas = getTransactionAttributeSource();
// 如果事务属性源对象为空或者事务属性对象不为null返回true，代表匹配成功；否则返回false，匹配失败
return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
}

获取事务属性对象，AbstractFallbackTransactionAttributeSource#getTransactionAttribute

public TransactionAttribute getTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
if (method.getDeclaringClass() == Object.class) {
return null;
}// First, see if we have a cached value.
Object cacheKey = getCacheKey(method, targetClass);
TransactionAttribute cached = this.attributeCache.get(cacheKey);
if (cached != null) {
// Value will either be canonical value indicating there is no transaction attribute,
// or an actual transaction attribute.
if (cached == NULL_TRANSACTION_ATTRIBUTE) {
return null;
}
else {
return cached;
}
}
else {
// 计算事务属性对象
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;
}
}

计算事务属性对象

protected TransactionAttribute computeTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
// Don't allow no-public methods as required.
if (allowPublicMethodsOnly() && !Modifier.isPublic(method.getModifiers())) {
return null;
}// The method may be on an interface, but we need attributes from the target class.
// If the target class is null, the method will be unchanged.
Method specificMethod = AopUtils.getMostSpecificMethod(method, targetClass);// First try is the method in the target class.
// 首先根据Method对象获取事务属性对象
TransactionAttribute txAttr = findTransactionAttribute(specificMethod);
if (txAttr != null) {
return txAttr;
}// Second try is the transaction attribute on the target class.
// 如果根据Method对象获取不到事务属性对象，那么根据Class来获取属性对象
txAttr = findTransactionAttribute(specificMethod.getDeclaringClass());
if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {
return txAttr;
}if (specificMethod != method) {
// Fallback is to look at the original method.
txAttr = findTransactionAttribute(method);
if (txAttr != null) {
return txAttr;
}
// Last fallback is the class of the original method.
txAttr = findTransactionAttribute(method.getDeclaringClass());
if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {
return txAttr;
}
}return null;
}

获取属性对象AnnotationTransactionAttributeSource#findTransactionAttribute

protected TransactionAttribute findTransactionAttribute(Class<?> clazz) {
return determineTransactionAttribute(clazz);
}

决定事务属性对象

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

解析事务属性对象，SpringTransactionAnnotationParser#parseTransactionAnnotation

public TransactionAttribute parseTransactionAnnotation(AnnotatedElement element) {
// 判断元素是否含有@Transactional注解，通过前面的分析我们可以得出如下结论：
// 1、首选判断类的方法上是否含有@Transactional注解，如果有就解析
// 2、如果所有的方法都不含有@Transactional注解，那么判断当前类是否含有@Transactional注解，如果有就解析
// 3、如果类或者类的某个方法含有@Transactional注解，那么事务属性对象就不为空，则说明次切面可以解析当前bean
AnnotationAttributes attributes = AnnotatedElementUtils.findMergedAnnotationAttributes(
element, Transactional.class, false, false);
if (attributes != null) {
return parseTransactionAnnotation(attributes);
}
else {
return null;
}
}

回到AbstractAutoProxyCreator#wrapIfNecessary

protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
return bean;
}
if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
return bean;
}
if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}// Create proxy if we have advice.
// 此处有值返回，进行代理，否则不进行代理
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
// 需要进行代理
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;
}

创建代理

创建代理AbstractAutoProxyCreator#createProxy

protected Object createProxy(Class<?> beanClass, @Nullable String beanName,
@Nullable Object[] specificInterceptors, TargetSource targetSource) {if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
} // 创建代理工厂
ProxyFactory proxyFactory = new ProxyFactory();
proxyFactory.copyFrom(this);if (!proxyFactory.isProxyTargetClass()) {
if (shouldProxyTargetClass(beanClass, beanName)) {
proxyFactory.setProxyTargetClass(true);
}
else {
evaluateProxyInterfaces(beanClass, proxyFactory);
}
} // 构建切面，此处的切面为BeanFactoryTransactionAttributeSourceAdvisor
Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
// 设置切面
proxyFactory.addAdvisors(advisors);
proxyFactory.setTargetSource(targetSource);
customizeProxyFactory(proxyFactory);proxyFactory.setFrozen(this.freezeProxy);
if (advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}return proxyFactory.getProxy(getProxyClassLoader());
}

获取代理ProxyFactory#getProxy

public Object getProxy(@Nullable ClassLoader classLoader) {
return createAopProxy().getProxy(classLoader);
}

创建aop代理

protected final synchronized AopProxy createAopProxy() {
if (!this.active) {
activate();
}
// 此处的this实际上就是ProxyFactory
return getAopProxyFactory().createAopProxy(this);
}

aop代理工厂创建aop代理DefaultAopProxyFactory#createAopProxy

public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {
Class<?> targetClass = config.getTargetClass();
if (targetClass == null) {
throw new AopConfigException("TargetSource cannot determine target class: " +
"Either an interface or a target is required for proxy creation.");
}
if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
return new JdkDynamicAopProxy(config);
}
// 创建cglib aop代理
return new ObjenesisCglibAopProxy(config);
}
else {
return new JdkDynamicAopProxy(config);
}
}

实例化ObjenesisCglibAopProxy对象

public ObjenesisCglibAopProxy(AdvisedSupport config) {
super(config);
}

父类实例化

public CglibAopProxy(AdvisedSupport config) throws AopConfigException {
Assert.notNull(config, "AdvisedSupport must not be null");
if (config.getAdvisors().length == 0 && config.getTargetSource() == AdvisedSupport.EMPTY_TARGET_SOURCE) {
throw new AopConfigException("No advisors and no TargetSource specified");
}
// 此处的config就是之前的ProxyFactory
this.advised = config;
this.advisedDispatcher = new AdvisedDispatcher(this.advised);
}

回到之前获取代理的地方

public Object getProxy(@Nullable ClassLoader classLoader) {
return createAopProxy().getProxy(classLoader);
}

通过上面的分析可以得知createAopProxy()返回的是CglibAopProxy

通过CglibAopProxy获取代理，CglibAopProxy#getProxy

public Object getProxy(@Nullable ClassLoader classLoader) {
if (logger.isTraceEnabled()) {
logger.trace("Creating CGLIB proxy: " + this.advised.getTargetSource());
}try {
Class<?> rootClass = this.advised.getTargetClass();
Assert.state(rootClass != null, "Target class must be available for creating a CGLIB proxy");Class<?> proxySuperClass = rootClass;
if (ClassUtils.isCglibProxyClass(rootClass)) {
proxySuperClass = rootClass.getSuperclass();
Class<?>[] additionalInterfaces = rootClass.getInterfaces();
for (Class<?> additionalInterface : additionalInterfaces) {
this.advised.addInterface(additionalInterface);
}
}// Validate the class, writing log messages as necessary.
validateClassIfNecessary(proxySuperClass, classLoader);// Configure CGLIB Enhancer...
// 创建Enhancer对象
Enhancer enhancer = createEnhancer();
if (classLoader != null) {
enhancer.setClassLoader(classLoader);
if (classLoader instanceof SmartClassLoader &&
((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {
enhancer.setUseCache(false);
}
}
// 设置父类
enhancer.setSuperclass(proxySuperClass);
// 设置接口
enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
enhancer.setStrategy(new ClassLoaderAwareUndeclaredThrowableStrategy(classLoader)); // 获取回调，重点分析
Callback[] callbacks = getCallbacks(rootClass);
Class<?>[] types = new Class<?>[callbacks.length];
for (int x = 0; x < types.length; x++) {
types[x] = callbacks[x].getClass();
}
// fixedInterceptorMap only populated at this point, after getCallbacks call above
enhancer.setCallbackFilter(new ProxyCallbackFilter(
this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset));
// 设置回调类型
enhancer.setCallbackTypes(types);// Generate the proxy class and create a proxy instance.
// 生成代理并创建代理实例
return createProxyClassAndInstance(enhancer, callbacks);
}
catch (CodeGenerationException | IllegalArgumentException ex) {
throw new AopConfigException("Could not generate CGLIB subclass of " + this.advised.getTargetClass() +
": Common causes of this problem include using a final class or a non-visible class",
ex);
}
catch (Throwable ex) {
// TargetSource.getTarget() failed
throw new AopConfigException("Unexpected AOP exception", ex);
}
}

获取回调

private Callback[] getCallbacks(Class<?> rootClass) throws Exception {
// Parameters used for optimization choices...
boolean exposeProxy = this.advised.isExposeProxy();
boolean isFrozen = this.advised.isFrozen();
boolean isStatic = this.advised.getTargetSource().isStatic();// Choose an "aop" interceptor (used for AOP calls).
// 实例化回调，在调用目标对象方法的时候执行
Callback aopInterceptor = new DynamicAdvisedInterceptor(this.advised);
return callbacks;
}

实例化回调部分

private static class DynamicAdvisedInterceptor implements MethodInterceptor, Serializable {private final AdvisedSupport advised;public DynamicAdvisedInterceptor(AdvisedSupport advised) {
// 设置切面信息，也就是之前的ProxyFactory
this.advised = advised;
}@Override
@Nullable
// 调用目标方法的时候执行
public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
Object oldProxy = null;
boolean setProxyContext = false;
Object target = null;
TargetSource targetSource = this.advised.getTargetSource();
try {
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);
// 获取通知，此处的通知为TransactionInterceptor
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
Object retVal;
// Check whether we only have one InvokerInterceptor: that is,
// no real advice, but just reflective invocation of the target.
if (chain.isEmpty() && Modifier.isPublic(method.getModifiers())) {
// 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);
retVal = methodProxy.invoke(target, argsToUse);
}
else {
// We need to create a method invocation...
retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();
}
retVal = processReturnType(proxy, target, method, retVal);
return retVal;
}
finally {
if (target != null && !targetSource.isStatic()) {
targetSource.releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}@Override
public boolean equals(Object other) {
return (this == other ||
(other instanceof DynamicAdvisedInterceptor &&
this.advised.equals(((DynamicAdvisedInterceptor) other).advised)));
}/**
* CGLIB uses this to drive proxy creation.
*/
@Override
public int hashCode() {
return this.advised.hashCode();
}
}

调用invocation的处理方法，ReflectiveMethodInvocation#proceed

public Object proceed() throws Throwable {
//We start with an index of -1 and increment early.
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
} // 此处的通知TransactionInterceptor
Object interceptorOrInterceptionAdvice =
this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
// Evaluate dynamic method matcher here: static part will already have
// been evaluated and found to match.
InterceptorAndDynamicMethodMatcher dm =
(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
Class<?> targetClass = (this.targetClass != null ? this.targetClass : this.method.getDeclaringClass());
if (dm.methodMatcher.matches(this.method, targetClass, this.arguments)) {
return dm.interceptor.invoke(this);
}
else {
// Dynamic matching failed.
// Skip this interceptor and invoke the next in the chain.
return proceed();
}
}
else {
// It's an interceptor, so we just invoke it: The pointcut will have
// been evaluated statically before this object was constructed.
// 调用TransactionInterceptor#invoke
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}

调用TransactionInterceptor#invoke

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...
// 以事务的方式进行调用
return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);
}

事务方式调用

protected Object invokeWithinTransaction(Method method, @Nullable Class<?> targetClass,
final InvocationCallback invocation) throws Throwable {// If the transaction attribute is null, the method is non-transactional.
TransactionAttributeSource tas = getTransactionAttributeSource();
final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
final PlatformTransactionManager tm = determineTransactionManager(txAttr);
final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
// Standard transaction demarcation with getTransaction and commit/rollback calls.
// 创建事务信息对象
TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
Object retVal = null;
try {
// This is an around advice: Invoke the next interceptor in the chain.
// This will normally result in a target object being invoked.
// 调用被代理对象方法
retVal = invocation.proceedWithInvocation();
}
catch (Throwable ex) {
// target invocation exception
// 业务方法执行异常，进行事务回滚
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
}
finally {
// 清除事务信息对象
cleanupTransactionInfo(txInfo);
}
// 提交事务
commitTransactionAfterReturning(txInfo);
return retVal;
}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;
}
}
}

到此事务的源码分析就结束了

专车总结

• 导入AutoProxyRegistrar、ProxyTransactionManagementConfiguration配置类
• AutoProxyRegistrar用来注册InfrastructureAdvisorAutoProxyCreator到IOC中，InfrastructureAdvisorAutoProxyCreator实现了BeanPostProcessor
• 执行BeanPostProcessor的后置处理
• 获取由ProxyTransactionManagementConfiguration配置类创建的切面
• 通过切面解析bean是否需要创建代理，需要就创建代理
• 执行代理的回调，在回调中拿到通知
• 执行通知，通知里面逻辑：开启事务、执行目标方法、提交或回滚事务

专车回顾

回顾下开头的两个问题：

• 为什么加上@Transactional注解就可以实现事务？
• 分析事务源码之后我们可以学到什么？

通过以上分析，第一个问题应该就迎刃而解了，那么通过以上学到的知识我们可以实现什么功能呢？在下一篇我们会在此基础上进行实战，通过@SystemLog注解实现系统日志功能。感谢各位撸友乘坐此趟专车，欢迎下次继续乘坐

最后

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