Understanding Spring's @Transactional Annotation and Its AOP Implementation

The @Transactional annotation is Spring's declarative transaction management mechanism that automatically opens, commits, or rolls back transactions using AOP.

Spring defines a pointcut for methods annotated with @Transactional so that during bean initialization it can decide whether to create a proxy for the bean.

During bean post‑processing, AnnotationAwareAspectJAutoProxyCreator invokes postProcessAfterInstantiation to generate a proxy if the pointcut matches, injecting a BeanFactoryTransactionAttributeSourceAdvisor as the advisor.

The proxy’s interceptor chain is built by

this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass)

, which includes a TransactionInterceptor that implements the transactional advice.

When a method is invoked, DynamicAdvisedInterceptor#intercept obtains the interceptor chain and creates a CglibMethodInvocation object that wraps the target method, arguments, and proxy.

The TransactionInterceptor#invoke method extracts the TransactionAttribute, determines the appropriate PlatformTransactionManager, and calls invokeWithinTransaction to manage the transaction lifecycle.

@Override
public Object invoke(final MethodInvocation invocation) throws Throwable {
    Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);
    return invokeWithinTransaction(invocation.getMethod(), targetClass, new InvocationCallback() {
        public Object proceedWithInvocation() throws Throwable {
            return invocation.proceed();
        }
    });
}

Inside invokeWithinTransaction, Spring creates a transaction if needed, executes the method, and on success commits the transaction; on exception it rolls back and re‑throws the error.

protected Object invokeWithinTransaction(Method method, Class<?> targetClass, final InvocationCallback invocation) throws Throwable {
    final TransactionAttribute txAttr = getTransactionAttributeSource().getTransactionAttribute(method, targetClass);
    final PlatformTransactionManager tm = determineTransactionManager(txAttr);
    TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, methodIdentification(method, targetClass));
    try {
        Object retVal = invocation.proceedWithInvocation();
        commitTransactionAfterReturning(txInfo);
        return retVal;
    } catch (Throwable ex) {
        completeTransactionAfterThrowing(txInfo, ex);
        throw ex;
    } finally {
        cleanupTransactionInfo(txInfo);
    }
}

The article concludes that the actual execution flow matches the earlier hypothesis, showing how Spring’s AOP infrastructure, advisors, and interceptors collaborate to provide transparent transaction management.