Spring事务实现原理
2022-07-26 本文已影响0人
神易风
代理对象在哪里创建
先从bean被创建后如何产生代理对象开始，在AbstractAutowireCapableBeanFactory.doCreateBean 初始化bean创建后，并且将依赖注入到bean中，在调用initializeBean 方法对刚刚完成依赖注入bean进行一次"初始化"
protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
}
if (mbd == null || !mbd.isSynthetic()) {
//就是在这里对符合条件bean 转换成 代理对象 对象 -> AnnotationAwareAspectJAutoProxyCreator
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
AbstractAutoProxyCreator.postProcessAfterInitialization
public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
if (bean != null) {
//判断Class FactoryBean 实现类，修改bean名字 在beanName前面加上&
Object cacheKey = getCacheKey(bean.getClass(), beanName);
if (this.earlyProxyReferences.remove(cacheKey) != bean) {
return wrapIfNecessary(bean, beanName, cacheKey); //这里将会返回代理后的对象
}
}
return bean;
}
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
//targetSourcedBeans 没有生成代理bean 缓存
if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
return bean;
}
//advisedBeans 也是缓存，返回false 则不会生成代理对象
if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
return bean;
}
//ORIGINAL 后置表明bean 实例不会变，则不会生成代理对象
if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
// Create proxy if we have advice.
//这里会返回 BeanFactoryTransactionAttributeSourceAdvisor,如果不创建代理对象，这里就会返回空数组
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE); //缓存已经解析过bean，后面就不用再解析一次class
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;
}
protected Object[] getAdvicesAndAdvisorsForBean(
Class<?> beanClass, String beanName, @Nullable TargetSource targetSource) {
//使用Advisor 去处理class 是否需要生成代理对象，如果需要则返回 advisors 不为空
List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
if (advisors.isEmpty()) {
return DO_NOT_PROXY;
}
return advisors.toArray();
}
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
//从容器中获取内置Advisor 使用一个Advisor 生成Advisor 通过代理工厂生成一堆代理对象
//这里会返回 BeanFactoryTransactionAttributeSourceAdvisor
List<Advisor> candidateAdvisors = findCandidateAdvisors();
List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
extendAdvisors(eligibleAdvisors);
if (!eligibleAdvisors.isEmpty()) {
eligibleAdvisors = sortAdvisors(eligibleAdvisors);
}
return eligibleAdvisors;
}
上面判断主要做一些检查，当所有状态合法后才会进入getAdvicesAndAdvisorsForBean返回通过指定bean生成的通知，在通过Advisor数组生成代理对象。这个方法主要逻辑就是通过
BeanFactoryTransactionAttributeSourceAdvisor 工厂内置Advisor解析Class并且生成pointcut 切点。主要实现在AopUtils
/**
* candidateAdvisors 内置Advisor 也就是BeanFactoryTransactionAttributeSourceAdvisor
* 给定Class 找寻可用Advisor
*/
public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) {
if (candidateAdvisors.isEmpty()) {
return candidateAdvisors;
}
List<Advisor> eligibleAdvisors = new ArrayList<>();
// IntroductionAdvisor只能应用于类级别 事务一般定位到Method上，不会使用这种类型Advisor
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;
}
// 这里会使用candidate 去解析Class 如果需要生成代理方法或者代理对象 将会返回true
if (canApply(candidate, clazz, hasIntroductions)) {
eligibleAdvisors.add(candidate);
}
}
return eligibleAdvisors;
}
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) {//代理一般都是方法层面，选用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;
}
}
//pointcut 为 TransactionAttributeSourcePointcut 内部类
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;
}
//方法匹配器，用于解析Method 是否需要生成代理方法
MethodMatcher methodMatcher = pc.getMethodMatcher();
if (methodMatcher == MethodMatcher.TRUE) { //没有任何逻辑，没有方法都会生成代理方法
// 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)) { //向上获取父类class，排除掉代理class
classes.add(ClassUtils.getUserClass(targetClass));
}
classes.addAll(ClassUtils.getAllInterfacesForClassAsSet(targetClass));
for (Class<?> clazz : classes) {
Method[] methods = ReflectionUtils.getAllDeclaredMethods(clazz);
for (Method method : methods) {
if (introductionAwareMethodMatcher != null ?
introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions) :
methodMatcher.matches(method, targetClass)) { //最终调用方法匹配器找到适合方法
return true;
}
}
}
return false;
}
本质依然是使用BeanFactoryTransactionAttributeSourceAdvisor 内部对象来匹配Class 或Method，并且生成Advisor。
主要流程使用BeanFactoryTransactionAttributeSourceAdvisor.Pointcut(TransactionAttributeSourcePointcut 抽象类) -> TransactionAttributeSourcePointcut.matches ->AbstractFallbackTransactionAttributeSource.getTransactionAttribute
-> AnnotationTransactionAttributeSource.findTransactionAttribute ->AnnotationTransactionAttributeSource.determineTransactionAttribute -> TransactionAnnotationParser.TransactionAttribute
其中在AnnotationTransactionAttributeSource.determineTransactionAttribute 方法会使用Spring 支持TransactionAnnotationParser 数组去解析method并且返回TransactionAttribute
TransactionAnnotationParser是Spring 事务注解解析器接口在Class、Method 上解析注解并且将声明注解解析成TransactionAttribute 支持3种实现
- SpringTransactionAnnotationParser Spring自身数据库事务 解析@Transactional
- Ejb3TransactionAnnotationParser EJB事务 解析 javax.ejb.TransactionAttribute
- JtaTransactionAnnotationParser JTA1.2 事务 解析javax.transaction.Transactional
我们一起看下如何生成代理对象的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);
}
ProxyFactory proxyFactory = new ProxyFactory();
proxyFactory.copyFrom(this);
if (!proxyFactory.isProxyTargetClass()) { // 如果还没有设置代理目标类这里在设置一次
if (shouldProxyTargetClass(beanClass, beanName)) {
proxyFactory.setProxyTargetClass(true);
}
else {
evaluateProxyInterfaces(beanClass, proxyFactory);
}
}
//这里返回Advisor 所以仍然是返回BeanFactoryTransactionAttributeSourceAdvisor
Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
proxyFactory.addAdvisors(advisors);
proxyFactory.setTargetSource(targetSource);
customizeProxyFactory(proxyFactory);
proxyFactory.setFrozen(this.freezeProxy);
if (advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}
// Use original ClassLoader if bean class not locally loaded in overriding class loader
ClassLoader classLoader = getProxyClassLoader();
if (classLoader instanceof SmartClassLoader && classLoader != beanClass.getClassLoader()) {
classLoader = ((SmartClassLoader) classLoader).getOriginalClassLoader();
}
// 这里有两个逻辑，一根据需求创建AopProxy 二 调用getProxy 创建代理对象
return proxyFactory.getProxy(classLoader);
}
调用AopProxy创建代理目标类，根据不同情况初始化不同AopProxy
public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {
@Override
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
// GraalVM Native Image 只支持 Dynamic proxy (java.lang.reflect.Proxy)
if (!NativeDetector.inNativeImage() &&
(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);
}
return new ObjenesisCglibAopProxy(config);
}
else {
return new JdkDynamicAopProxy(config);
}
}
/**
* Determine whether the supplied {@link AdvisedSupport} has only the
* {@link org.springframework.aop.SpringProxy} interface specified
* (or no proxy interfaces specified at all).
*/
private boolean hasNoUserSuppliedProxyInterfaces(AdvisedSupport config) {
Class<?>[] ifcs = config.getProxiedInterfaces();
return (ifcs.length == 0 || (ifcs.length == 1 && SpringProxy.class.isAssignableFrom(ifcs[0])));
}
}
其中JdkDynamicAopProxy 是通过InvocationHandler 接口实现，ObjenesisCglibAopProxy就是通过Cglib实现，这次只有看下Cglib如何创建动态对象的
public Object getProxy(@Nullable ClassLoader classLoader) {
try {
Class<?> rootClass = this.advised.getTargetClass();
Assert.state(rootClass != null, "Target class must be available for creating a CGLIB proxy");
Class<?> proxySuperClass = rootClass;
if (rootClass.getName().contains(ClassUtils.CGLIB_CLASS_SEPARATOR)) {
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...
//Cglib 核心就是通过Enhancer 对象去创建代理
Enhancer enhancer = createEnhancer();
if (classLoader != null) {
enhancer.setClassLoader(classLoader);
if (classLoader instanceof SmartClassLoader &&
((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {
enhancer.setUseCache(false);
}
}
enhancer.setSuperclass(proxySuperClass);
enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
enhancer.setStrategy(new ClassLoaderAwareGeneratorStrategy(classLoader));
//这里将Spring 内置7MethodInterceptor 实现
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));
enhancer.setCallbackTypes(types);
// Generate the proxy class and create a proxy instance.
return createProxyClassAndInstance(enhancer, callbacks);
}
}
Cglib样例
编写一个简单Demo类，对方法进行前后增强。
public class Demo {
public void call(){
System.out.println("我就是目标类原始方法");
}
}
编写拦截器
public class CglibMethodInterceptor implements MethodInterceptor {
/**
* 通过在intercept 上重写方法达到通知增强逻辑
* @param o 代表Cglib 生成的动态代理类 对象本身
* @param method 代理类中被拦截的接口方法 Method 实例
* @param objects 接口方法参数
* @param methodProxy 用于调用父类真正的业务类方法。可以直接调用被代理类接口方法 原始方法
* @return
* @throws Throwable
*/
@Override
public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
System.out.println("invoke before....");
MonitorUtil.start();
Object invoke = methodProxy.invokeSuper(o, objects);
//Object invoke = method.invoke(o,objects); 这样会导致栈溢出
System.out.println("invoken after");
MonitorUtil.finish();
return invoke;
}
}
最后创建代理对象
@Test
public void cglibTest(){
Enhancer enhancer = new Enhancer();
enhancer.setClassLoader(this.getClass().getClassLoader());
enhancer.setSuperclass(Demo.class);
enhancer.setCallback(new CglibMethodInterceptor());
Demo proxyInst = (Demo) enhancer.create();
proxyInst.call();
}
执行结果
invoke before....
我就是目标类原始方法
invoken after
其实跟JDK动态代理写法差不多，都是通过在原始方法前后插入代码，达到增强。CGLIB支持多个MethodInterceptor，组成一个拦截器链，按照一定顺序执行intercept。这种方法有利于AOP结构和代理业务代码解耦。
事务如何通过代理来实现的
通过上面一个小例子，我们已经了解到实现代理逻辑核心就是getCallbacks(rootClass) 返回拦截器，内置拦截器有7种，事务实现类就是在CglibAopProxy.DynamicAdvisedInterceptor。
private static class DynamicAdvisedInterceptor implements MethodInterceptor, Serializable {
private final AdvisedSupport advised;
public DynamicAdvisedInterceptor(AdvisedSupport advised) {
this.advised = advised;
}
@Override
@Nullable
public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
Object oldProxy = null;
boolean setProxyContext = false;
Object target = null;
TargetSource targetSource = this.advised.getTargetSource();
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);
//这里会返回TransactionInterceptor 事务执行核心类
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())) { //没有代理拦截器
// 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... 在这里执行事务
retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();
}
retVal = processReturnType(proxy, target, method, retVal); //包装返回类型
return retVal;
}
finally {
if (target != null && !targetSource.isStatic()) {
targetSource.releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}
这个内部类主要就是两个核心方法getInterceptorsAndDynamicInterceptionAdvice，从BeanFactoryTransactionAttributeSourceAdvisor.pointcut 返回MethodInterceptor 实现类TransactionInterceptor 并且使用InterceptorAndDynamicMethodMatcher 将返回MethodInterceptor、MethodMatcher 包装起来，下面会使用到的。
将拦截器执行链作为构造器参数初始化CglibMethodInvocation，调用proceed 执行事务，proceed 会调用父类ReflectiveMethodInvocation.proceed，核心逻辑就在里面了。
public Object proceed() throws Throwable {
// We start with an index of -1 and increment early.
// currentInterceptorIndex 默认是-1 相等表示拦截器链里面没有代理方法，直接执行原方法
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
}
//从第一个开始执行
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());
//dm 就是上面写到TransactionAnnotationParser
if (dm.methodMatcher.matches(this.method, targetClass, this.arguments)) {
return dm.interceptor.invoke(this); //调用TransactionInterceptor.invoke
}
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.
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
这里使用递归方式执行调用链
TransactionInterceptor 可以说是Spring事务执行器了，它负责执行事务，它自己本身没有任务事务实现代码，都是通TransactionManager 事务管理器来实现事务开始、回滚、提交。
直接从TransactionInterceptor.invoke 开始分析
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...
//这里调用父类TransactionAspectSupport.invokeWithinTransaction
return invokeWithinTransaction(invocation.getMethod(), targetClass, new CoroutinesInvocationCallback() {
@Override
@Nullable
public Object proceedWithInvocation() throws Throwable {
return invocation.proceed();
}
@Override
public Object getTarget() {
return invocation.getThis();
}
@Override
public Object[] getArguments() {
return invocation.getArguments();
}
});
}
invokeWithinTransaction 看方法吗方法命名就知道干什么的，执行事务方法。三个参数
Method 要执行方法，主要是获取事务注解上属性
Class 被代理Class，作业跟Method差不多
InvocationCallback 被实现的class，主要用于执行代理方法。要知道Spring AOP是代理chain 方式执行，一个类不单止是被事务代理的，还有会因为其他业务被代理了，保证代理链能全部执行下去。
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();
//TransactionAttribute 是执行事务必须实体 包含很多重要信息 事务隔离级别、事务传播级别、异常回滚等
final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
//获取TransactionManager 事务管理器，再平常开发中可以存在自己配置事务管理器情况，先读取@Transactional value 属性，
//没有从transactionManagerBeanName 可以从配置文件指定
//最后就是Spring默认事务实现
final TransactionManager tm = determineTransactionManager(txAttr);
if (this.reactiveAdapterRegistry != null && tm instanceof ReactiveTransactionManager) {
//这里是反应式事务 Mongdb NOSQL使用，这里略过
}
PlatformTransactionManager ptm = asPlatformTransactionManager(tm);
final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);
// CallbackPreferringPlatformTransactionManager 是 PlatformTransactionManager 扩展接口提供在执行事务时暴露一个回调方法
if (txAttr == null || !(ptm instanceof CallbackPreferringPlatformTransactionManager)) {
// Standard transaction demarcation with getTransaction and commit/rollback calls.
// 获取正在执行的事务状态或者创建一个事务 TransactionInfo 事务状态 会记录事务执行，用于回滚
TransactionInfo txInfo = createTransactionIfNecessary(ptm, txAttr, joinpointIdentification);
Object retVal;
try {
// This is an around advice: Invoke the next interceptor in the chain.
// This will normally result in a target object being invoked.
// invocation 就是被实现类，调用原始方法或者代理方法
// 其实这里就是around advice 环绕通知 前面开启事务，下面方法负责回滚或提交
retVal = invocation.proceedWithInvocation();
}
catch (Throwable ex) {
// target invocation exception
//处理业务异常，如果异常符合回滚，就会回滚否则就是commit
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
}
finally {
// 在ThreadLocal 清除事务状态txInfo
//要知道所有事务都通过ThreadLocal 进行传递
//在正常或者异常情况下，清除线程绑定事务
cleanupTransactionInfo(txInfo);
}
//处理下返回值，使用了io.vavr.control.Try 来处理，没用过 略过下面
if (retVal != null && vavrPresent && VavrDelegate.isVavrTry(retVal)) {
// Set rollback-only in case of Vavr failure matching our rollback rules...
TransactionStatus status = txInfo.getTransactionStatus();
if (status != null && txAttr != null) {
retVal = VavrDelegate.evaluateTryFailure(retVal, txAttr, status);
}
}
//这个说的很明白 处理完返回值后再进行提交事务
commitTransactionAfterReturning(txInfo);
return retVal;
}
else { //这个是CallbackPreferringPlatformTransactionManager 执行事务方式
//跟上面处理差不多就是多了一个execute 方法，在回调函数去执行事务，相当于将事务执行交给调用者去实现
Object result;
final ThrowableHolder throwableHolder = new ThrowableHolder();
// It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.
try {
result = ((CallbackPreferringPlatformTransactionManager) ptm).execute(txAttr, status -> {
TransactionInfo txInfo = prepareTransactionInfo(ptm, txAttr, joinpointIdentification, status);
try {
Object retVal = invocation.proceedWithInvocation();
if (retVal != null && vavrPresent && VavrDelegate.isVavrTry(retVal)) {
// Set rollback-only in case of Vavr failure matching our rollback rules...
retVal = VavrDelegate.evaluateTryFailure(retVal, txAttr, status);
}
return retVal;
}
catch (Throwable ex) {
if (txAttr.rollbackOn(ex)) {
// A RuntimeException: will lead to a rollback.
if (ex instanceof RuntimeException) {
throw (RuntimeException) ex;
}
else {
throw new ThrowableHolderException(ex);
}
}
else {
// A normal return value: will lead to a commit.
throwableHolder.throwable = ex;
return null;
}
}
finally {
cleanupTransactionInfo(txInfo);
}
});
}
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;
}
// Check result state: It might indicate a Throwable to rethrow.
if (throwableHolder.throwable != null) {
throw throwableHolder.throwable;
}
return result;
}
}
总结
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在这篇文章中我们简单学习了Spring初始化bean时，如何将bean创建成一个代理对象，并且使用Cglib技术创建一个代理bean，在结合事务管理器分析了代理如何去实现Spring事务的。使用一个小例子演示了Cglib代理如何实现的，方便理解Spring AOP代理是通过一个拦截器去实现的，一个对象的多个代理封装到调用链里面，执行方法时顺序执行，保证每一个代理与代理之间没有任何联系，相互独立。这次我还了解了Spring代理机制原理，通过Advisor实现类去解析Class、Method，通过PointcutAdvisor(匹配Class、Method)、IntroductionAdvisor (支持Class)是否需要生成代理对象。然后在通过专门代理工程去生成对应代理对象。
我们简单了解事务实现，其实就是环绕通知实现而已，还了解到事务状态传递是通过ThreadLocal来实现的。
