Spring5 源码阅读笔记（4.1）事务切面的 invoke_invoke 事务

前置文章
Spring5 源码阅读笔记（3.3）JDKDynamicAopProxy 的 invoke 调用
Spring5 源码阅读笔记（4）事务：@EnableTransactionManagement 做了什么？

当我们执行一段打了 @Transactional 的代码时，其实是会走到 JDKDynamicAopProxy 的 invoke 方法的（如果用的是 JDKDynamicAopProxy ）。

这时候，chain 里会有一个 TransactionInterceptor，然后会调用 invocation.proceed()。

类 ReflectiveMethodInvocation

@Override
@Nullable
public Object proceed() throws Throwable {
	//	We start with an index of -1 and increment early.
	//如果执行链中的advice全部执行完，则直接调用joinPoint方法，就是被代理方法
	if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
		return invokeJoinpoint();
	}

	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MethodInterceptor中的invoke方法
		return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
	}
}
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跟 invoke：
MethodInterceptor

类 TransactionInterceptor

@Override
@Nullable
public Object invoke(MethodInvocation invocation) throws Throwable {
	// Work out the target class: may be {@code null}.
	// The TransactionAttributeSource should be passed the target class
	// as well as the method, which may be from an interface.
	Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);

	// Adapt to TransactionAspectSupport's invokeWithinTransaction...
	return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);
}
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跟 invokeWithinTransaction：
类 TransactionAspectSupport

@Nullable
protected Object invokeWithinTransaction(Method method, @Nullable Class<?> targetClass,
		final InvocationCallback invocation) throws Throwable {

	// If the transaction attribute is null, the method is non-transactional.
	//获取 AnnotationTransactionAttributeSource，能解析 @Transactional ，见4
	TransactionAttributeSource tas = getTransactionAttributeSource();

	//获取方法上面有@Transactional注解的属性，用的是4里的SpringTransactionAnnotationParser                   
	final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);

	//获取事务管理器
	final PlatformTransactionManager tm = determineTransactionManager(txAttr);
	//被代理方法
	final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);

	if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
		// Standard transaction demarcation with getTransaction and commit/rollback calls.
								//见4.1.1
		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.
			//火炬传递
			//如果有另外的切面，走到另外的切面；没有，调用被代理方法
			retVal = invocation.proceedWithInvocation();
		}
		catch (Throwable ex) {
			// target invocation exception
			//事务回滚 见 4.1.2
			completeTransactionAfterThrowing(txInfo, ex);
			//抛异常
			throw ex;
		}
		finally {
			cleanupTransactionInfo(txInfo);
		}
		//事务提交 见 4.1.3
		commitTransactionAfterReturning(txInfo);
		return retVal;
	}

	//不用看
	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;
		}
	}
}
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