代理对象在哪里创立
先从 bean 被创立后如何产生代理对象开始，在AbstractAutowireCapableBeanFactory.doCreateBean 初始化 bean 创立后，并且将依赖注入到 bean 中，在调用 initializeBean 办法对刚刚实现依赖注入 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，批改 bean 名字 在 beanName 后面加上 &
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, 如果不创立代理对象，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); // 缓存曾经解析过 bean，前面就不必再解析一次 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) {
// 应用 Advisor 去解决 class 是否须要生成代理对象，如果须要则返回 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 应用一个 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;
}下面判断次要做一些查看，当所有状态非法后才会进入 getAdvicesAndAdvisorsForBean 返回通过指定 bean 生成的告诉，在通过 Advisor 数组生成代理对象。这个办法次要逻辑就是通过
BeanFactoryTransactionAttributeSourceAdvisor 工厂内置 Advisor 解析 Class 并且生成 pointcut 切点。次要实现在 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 只能利用于类级别 事务个别定位到 Method 上，不会应用这种类型 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;
}
// 这里会应用 candidate 去解析 Class 如果须要生成代理办法或者代理对象 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) {// 代理个别都是办法层面，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 外部类
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;}
// 办法匹配器，用于解析 Method 是否须要生成代理办法
MethodMatcher methodMatcher = pc.getMethodMatcher();
if (methodMatcher == MethodMatcher.TRUE) { // 没有任何逻辑，没有办法都会生成代理办法
// 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)) { // 最终调用办法匹配器找到适宜办法
return true;
}
}
}
return false;
}实质仍然是应用 BeanFactoryTransactionAttributeSourceAdvisor 外部对象来匹配 Class 或 Method，并且生成 Advisor。
次要流程应用 BeanFactoryTransactionAttributeSourceAdvisor.Pointcut(TransactionAttributeSourcePointcut 抽象类) -> TransactionAttributeSourcePointcut.matches ->AbstractFallbackTransactionAttributeSource.getTransactionAttribute
-> AnnotationTransactionAttributeSource.findTransactionAttribute ->AnnotationTransactionAttributeSource.determineTransactionAttribute -> TransactionAnnotationParser.TransactionAttribute
其中在 AnnotationTransactionAttributeSource.determineTransactionAttribute 办法会应用 Spring 反对 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 上解析注解并且将申明注解解析成 TransactionAttribute 反对 3 种实现
- SpringTransactionAnnotationParser Spring 本身数据库事务 解析 @Transactional
- Ejb3TransactionAnnotationParser EJB 事务 解析 javax.ejb.TransactionAttribute
- JtaTransactionAnnotationParser JTA1.2 事务 解析 javax.transaction.Transactional
咱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指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 所以依然是返回 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，一依据需要创立 AopProxy 二 调用 getProxy 创立代理对象
return proxyFactory.getProxy(classLoader);
}调用 AopProxy 创立代理指标类，依据不同状况初始化不同 AopProxy
public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {
@Override
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {// GraalVM Native Image 只反对 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 如何创立动静对象的
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 外围就是通过 Enhancer 对象去创立代理
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
编写一个简略 Demo 类，对办法进行前后加强。
public class Demo {public void call(){System.out.println("我就是指标类原始办法");
}
}编写拦截器
public class CglibMethodInterceptor implements MethodInterceptor {
/**
* 通过在 intercept 上重写办法达到告诉加强逻辑
* @param o 代表 Cglib 生成的动静代理类 对象自身
* @param method 代理类中被拦挡的接口办法 Method 实例
* @param objects 接口办法参数
* @param methodProxy 用于调用父类真正的业务类办法。能够间接调用被代理类接口办法 原始办法
* @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;
}
}最初创立代理对象
@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();}执行后果
invoke before….
我就是指标类原始办法
invoken after
其实跟 JDK 动静代理写法差不多，都是通过在原始办法前后插入代码，达到加强。CGLIB 反对多个 MethodInterceptor，组成一个拦截器链，依照肯定程序执行 intercept。这种办法有利于 AOP 构造和代理业务代码解耦。
事务如何通过代理来实现的
通过下面一个小例子，咱们曾经理解到实现代理逻辑外围就是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 事务执行外围类
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);
}
}
}这个外部类次要就是两个外围办法 getInterceptorsAndDynamicInterceptionAdvice，从 BeanFactoryTransactionAttributeSourceAdvisor.pointcut 返回 MethodInterceptor 实现类 TransactionInterceptor 并且应用 InterceptorAndDynamicMethodMatcher 将返回 MethodInterceptor、MethodMatcher 包装起来，上面会应用到的。
将拦截器执行链作为结构器参数初始化 CglibMethodInvocation，调用 proceed 执行事务，proceed 会调用父类 ReflectiveMethodInvocation.proceed，外围逻辑就在外面了。
public Object proceed() throws Throwable {
// We start with an index of -1 and increment early.
// currentInterceptorIndex 默认是 -1 相等示意拦截器链外面没有代理办法，间接执行原办法
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 就是下面写到 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);
}
}
这里应用递归形式执行调用链
TransactionInterceptor 能够说是 Spring 事务执行器了，它负责执行事务，它本人自身没有工作事务实现代码，都是通 TransactionManager 事务管理器来实现事务开始、回滚、提交。
间接从 TransactionInterceptor.invoke 开始剖析
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 看办法吗办法命名就晓得干什么的，执行事务办法。三个参数
Method 要执行办法，次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，次要用于执行代理办法。要晓得 Spring AOP 是代理 chain 形式执行，一个类不单止是被事务代理的，还有会因为其余业务被代理了，保障代理链能全副执行上来。
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 蕴含很多重要信息 事务隔离级别、事务流传级别、异样回滚等
final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
// 获取 TransactionManager 事务管理器，再平时开发中能够存在本人配置事务管理器状况，先读取 @Transactional value 属性，// 没有从 transactionManagerBeanName 能够从配置文件指定
// 最初就是 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 应用，这里略过}
PlatformTransactionManager ptm = asPlatformTransactionManager(tm);
final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);
// CallbackPreferringPlatformTransactionManager 是 PlatformTransactionManager 扩大接口提供在执行事务时裸露一个回调办法
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立一个事务 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，调用原始办法或者代理办法
// 其实这里就是 around advice 盘绕告诉 后面开启事务，上面办法负责回滚或提交
retVal = invocation.proceedWithInvocation();}
catch (Throwable ex) {
// target invocation exception
// 解决业务异样，如果异样合乎回滚，就会回滚否则就是 commit
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
}
finally {
// 在 ThreadLocal 革除事务状态 txInfo
// 要晓得所有事务都通过 ThreadLocal 进行传递
// 在失常或者异常情况下，革除线程绑定事务
cleanupTransactionInfo(txInfo);
}
// 解决下返回值，应用了 io.vavr.control.Try 来解决，没用过 略过上面
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);
}
}
// 这个说的很明确 解决完返回值后再进行提交事务
commitTransactionAfterReturning(txInfo);
return retVal;
}
else { // 这个是 CallbackPreferringPlatformTransactionManager 执行事务形式
// 跟下面解决差不多就是多了一个 execute 办法，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
在这篇文章中咱们简略学习了 Spring 初始化 bean 时，如何将 bean 创立成一个代理对象，并且应用 Cglib 技术创立一个代理 bean，在联合事务管理器剖析了代理如何去实现 Spring 事务的。应用一个小例子演示了 Cglib 代理如何实现的，不便了解 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外面，执行办法时程序执行，保障每一个代理与代理之间没有任何分割，互相独立。这次我还理解了 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 (反对 Class)是否须要生成代理对象。而后在通过专门代理工程去生成对应代理对象。
咱们简略理解事务实现，其实就是盘绕告诉实现而已，还理解到事务状态传递是通过 ThreadLocal 来实现的。