【原創】002 | 搭上SpringBoot事務原始碼分析專車
阿新 • • 發佈：2019-12-10
前言
如果這是你第二次看到師長，說明你在覬覦我的美色!
點贊+關注再看，養成習慣
沒別的意思，就是需要你的窺屏^_^
專車介紹**
該趟專車是開往Spring Boot事務原始碼分析的專車
專車問題
- 為什麼加上@Transactional註解就可以實現事務？
- 分析事務原始碼之後我們可以學到什麼？
專車名詞
事務
程式中通常使用事務來達到資料的一致性，從而避免髒資料
程式設計式事務
在業務方法開頭開啟事務，然後對我們的業務進行try-catch，假設沒有異常則提交事務，如果出現異常，則在catch模組回滾事務
宣告式事務由來
如果採用程式設計式事務，那麼在任何需要事務的地方都要開啟事務、try-catch、提交或者回滾事務，會導致重複編碼、編寫與業務無關的程式碼。基於Spring Aop思想，我們可以利用Aop的方式，對需要使用事務的方法進行增強，將公用的部分提取出來，那麼就實現了宣告式事務。
Spring提供的宣告式事務
在需要使用事務的業務方法上新增@Transactional註解，那麼就可以使用事務的特性，要麼成功，要麼失敗
Spring Aop核心概念
- 切面：切面是由切點和通知組成
- 切點：用來匹配符合條件類或方法
- 通知：需要執行的操作
專車分析
基於Spring Boot自動配置原理，我們應該尋找xxxAutoConfiguration自動配置類，此處要尋找和事務相關的，那麼自然是TransactionAutoConfiguration
自動配置
開啟TransactionAutoConfiguration自動配置類
@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 { } }
可以看到開啟事務管理器的註解@EnableTransactionManagement
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(TransactionManagementConfigurationSelector.class)
public @interface EnableTransactionManagement {}檢視TransactionManagementConfigurationSelector匯入的類
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; } }
可以看到匯入了AutoProxyRegistrar和ProxyTransactionManagementConfiguration
首先看看AutoProxyRegistrar，該類實現了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) {
// 註冊自動代理建立器
AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
if ((Boolean) proxyTargetClass) {
AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
return;
}
}
}
}
}註冊自動代理建立器，AopConfigUtils#registerAutoProxyCreatorIfNecessary
public static BeanDefinition registerAutoProxyCreatorIfNecessary(
BeanDefinitionRegistry registry, @Nullable Object source) {
// 註冊了InfrastructureAdvisorAutoProxyCreator到IOC容器中
return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
}InfrastructureAdvisorAutoProxyCreator是AbstractAutoProxyCreator的子類，AbstractAutoProxyCreator又實現了BeanPostProcessor介面，那麼在bean初始化完畢後就會呼叫postProcessAfterInstantiation()方法，postProcessAfterInstantiation()定義在AbstractAutoProxyCreator類中
BeanPostProcessor後置處理
開啟AbstractAutoProxyCreator
@Override
public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
if (bean != null) {
Object cacheKey = getCacheKey(bean.getClass(), beanName);
if (!this.earlyProxyReferences.contains(cacheKey)) {
// 如果滿足條件對bean進行包裹
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}該方法呼叫了wrapIfNecessary()方法
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
// Create proxy if we have advice.
// 獲取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);
// 建立代理
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;
}根據註釋的意思就是如果存在advice，那麼就建立代理，
尋找切面
進入AbstractAdvisorAutoProxyCreator#getAdvicesAndAdvisorsForBean
protected Object[] getAdvicesAndAdvisorsForBean(
Class<?> beanClass, String beanName, @Nullable TargetSource targetSource) {
// 查詢符合條件的切面
List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
// 不存在符合條件的切面，則不生成代理
if (advisors.isEmpty()) {
return DO_NOT_PROXY;
}
return advisors.toArray();
}該程式碼第一句最重要，如果不存在符合條件的切面，那麼最終的結果返回null，根據上面分析的，如果為null就不建立代理，否則建立代理。接下來看看第一句的實現
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
// 獲取所有候選的切面，也就是型別為Advisor的切面，此處獲取到的候選切面為BeanFactoryTransactionAttributeSourceAdvisor
List<Advisor> candidateAdvisors = findCandidateAdvisors();
// 從候選的切面中獲取可以解析當前bean的切面，最終符合條件的切面為BeanFactoryTransactionAttributeSourceAdvisor
List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
extendAdvisors(eligibleAdvisors);
if (!eligibleAdvisors.isEmpty()) {
eligibleAdvisors = sortAdvisors(eligibleAdvisors);
}
return eligibleAdvisors;
}
為什麼上面獲取到的切面是BeanFactoryTransactionAttributeSourceAdvisor？是否還記得之前匯入配置類的時候還有一個配置類沒有分析？那就是ProxyTransactionManagementConfiguration
開啟ProxyTransactionManagementConfiguration
@Configuration
public class ProxyTransactionManagementConfiguration extends AbstractTransactionManagementConfiguration {
// 建立BeanFactoryTransactionAttributeSourceAdvisor
@Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor() {
BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();
advisor.setTransactionAttributeSource(transactionAttributeSource());
// 設定切面對應的通知，後面分析會用到
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();
}
// 建立通知
@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;
}
}
通過上面的自動配置，可得知獲取到的候選切面為什麼是BeanFactoryTransactionAttributeSourceAdvisor
接下來看看如何從候選切面中找到可以解析當前bean的切面？
protected List<Advisor> findAdvisorsThatCanApply(
List<Advisor> candidateAdvisors, Class<?> beanClass, String beanName) {
ProxyCreationContext.setCurrentProxiedBeanName(beanName);
try {
// 查詢可以解析當前bean對應的切面
return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
}
finally {
ProxyCreationContext.setCurrentProxiedBeanName(null);
}
}
查詢可以解析當前bean對應的切面，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;
}
// 當前切面是否可以解析bean
if (canApply(candidate, clazz, hasIntroductions)) {
eligibleAdvisors.add(candidate);
}
}
return eligibleAdvisors;
}
候選切面是否可以解析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) {
// 由上面分析知道最終的候選切面為BeanFactoryTransactionAttributeSourceAdvisor
// 該類實現了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;
}
}
候選切面是否可以解析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;
}
// 獲取切面切點方法匹配物件，用來匹配方法是否符合
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) {
// 通過反射獲取當前類所有的Method物件
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();
// 如果事務屬性源物件為空或者事務屬性物件不為null返回true，代表匹配成功；否則返回false，匹配失敗
return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
}
獲取事務屬性物件，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 {
// 計算事務屬性物件
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;
}
}
計算事務屬性物件
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.
// 首先根據Method物件獲取事務屬性物件
TransactionAttribute txAttr = findTransactionAttribute(specificMethod);
if (txAttr != null) {
return txAttr;
}
// Second try is the transaction attribute on the target class.
// 如果根據Method物件獲取不到事務屬性物件，那麼根據Class來獲取屬性物件
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;
}
獲取屬性物件AnnotationTransactionAttributeSource#findTransactionAttribute
protected TransactionAttribute findTransactionAttribute(Class<?> clazz) {
return determineTransactionAttribute(clazz);
}
決定事務屬性物件
protected TransactionAttribute determineTransactionAttribute(AnnotatedElement element) {
for (TransactionAnnotationParser annotationParser : this.annotationParsers) {
TransactionAttribute attr = annotationParser.parseTransactionAnnotation(element);
if (attr != null) {
return attr;
}
}
return null;
}
解析事務屬性物件，SpringTransactionAnnotationParser#parseTransactionAnnotation
public TransactionAttribute parseTransactionAnnotation(AnnotatedElement element) {
// 判斷元素是否含有@Transactional註解，通過前面的分析我們可以得出如下結論：
// 1、首選判斷類的方法上是否含有@Transactional註解，如果有就解析
// 2、如果所有的方法都不含有@Transactional註解，那麼判斷當前類是否含有@Transactional註解，如果有就解析
// 3、如果類或者類的某個方法含有@Transactional註解，那麼事務屬性物件就不為空，則說明次切面可以解析當前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.
// 此處有值返回，進行代理，否則不進行代理
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
// 需要進行代理
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
// 建立代理
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;
}
建立代理
建立代理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);
}
// 建立代理工廠
ProxyFactory proxyFactory = new ProxyFactory();
proxyFactory.copyFrom(this);
if (!proxyFactory.isProxyTargetClass()) {
if (shouldProxyTargetClass(beanClass, beanName)) {
proxyFactory.setProxyTargetClass(true);
}
else {
evaluateProxyInterfaces(beanClass, proxyFactory);
}
}
// 構建切面，此處的切面為BeanFactoryTransactionAttributeSourceAdvisor
Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
// 設定切面
proxyFactory.addAdvisors(advisors);
proxyFactory.setTargetSource(targetSource);
customizeProxyFactory(proxyFactory);
proxyFactory.setFrozen(this.freezeProxy);
if (advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}
return proxyFactory.getProxy(getProxyClassLoader());
}
獲取代理ProxyFactory#getProxy
public Object getProxy(@Nullable ClassLoader classLoader) {
return createAopProxy().getProxy(classLoader);
}
建立aop代理
protected final synchronized AopProxy createAopProxy() {
if (!this.active) {
activate();
}
// 此處的this實際上就是ProxyFactory
return getAopProxyFactory().createAopProxy(this);
}
aop代理工廠建立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);
}
// 建立cglib aop代理
return new ObjenesisCglibAopProxy(config);
}
else {
return new JdkDynamicAopProxy(config);
}
}
例項化ObjenesisCglibAopProxy物件
public ObjenesisCglibAopProxy(AdvisedSupport config) {
super(config);
}
父類例項化
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");
}
// 此處的config就是之前的ProxyFactory
this.advised = config;
this.advisedDispatcher = new AdvisedDispatcher(this.advised);
}
回到之前獲取代理的地方
public Object getProxy(@Nullable ClassLoader classLoader) {
return createAopProxy().getProxy(classLoader);
}
通過上面的分析可以得知createAopProxy()返回的是CglibAopProxy
通過CglibAopProxy獲取代理，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...
// 建立Enhancer物件
Enhancer enhancer = createEnhancer();
if (classLoader != null) {
enhancer.setClassLoader(classLoader);
if (classLoader instanceof SmartClassLoader &&
((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {
enhancer.setUseCache(false);
}
}
// 設定父類
enhancer.setSuperclass(proxySuperClass);
// 設定介面
enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
enhancer.setStrategy(new ClassLoaderAwareUndeclaredThrowableStrategy(classLoader));
// 獲取回撥，重點分析
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));
// 設定回撥型別
enhancer.setCallbackTypes(types);
// Generate the proxy class and create a proxy instance.
// 生成代理並建立代理例項
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);
}
}
獲取回撥
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).
// 例項化回撥，在呼叫目標物件方法的時候執行
Callback aopInterceptor = new DynamicAdvisedInterceptor(this.advised);
return callbacks;
}
例項化回撥部分
private static class DynamicAdvisedInterceptor implements MethodInterceptor, Serializable {
private final AdvisedSupport advised;
public DynamicAdvisedInterceptor(AdvisedSupport advised) {
// 設定切面資訊，也就是之前的ProxyFactory
this.advised = advised;
}
@Override
@Nullable
// 呼叫目標方法的時候執行
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);
// 獲取通知，此處的通知為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();
}
}
呼叫invocation的處理方法，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();
}
// 此處的通知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.
// 呼叫TransactionInterceptor#invoke
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
呼叫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...
// 以事務的方式進行呼叫
return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);
}
事務方式呼叫
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.
// 建立事務資訊物件
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.
// 呼叫被代理物件方法
retVal = invocation.proceedWithInvocation();
}
catch (Throwable ex) {
// target invocation exception
// 業務方法執行異常，進行事務回滾
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
}
finally {
// 清除事務資訊物件
cleanupTransactionInfo(txInfo);
}
// 提交事務
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;
}
}
}
到此事務的原始碼分析就結束了
專車總結
- 匯入AutoProxyRegistrar、ProxyTransactionManagementConfiguration配置類
- AutoProxyRegistrar用來註冊InfrastructureAdvisorAutoProxyCreator到IOC中，InfrastructureAdvisorAutoProxyCreator實現了BeanPostProcessor
- 執行BeanPostProcessor的後置處理
- 獲取由ProxyTransactionManagementConfiguration配置類建立的切面
- 通過切面解析bean是否需要建立代理，需要就建立代理
- 執行代理的回撥，在回撥中拿到通知
- 執行通知，通知裡面邏輯：開啟事務、執行目標方法、提交或回滾事務
專車回顧
回顧下開頭的兩個問題：
- 為什麼加上@Transactional註解就可以實現事務？
- 分析事務原始碼之後我們可以學到什麼？
通過以上分析，第一個問題應該就迎刃而解了，那麼通過以上學到的知識我們可以實現什麼功能呢？在下一篇我們會在此基礎上進行實戰，通過@SystemLog註解實現系統日誌功能。感謝各位擼友乘坐此趟專車，歡迎下次繼續乘坐
最後
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