Understanding Spring's @Transactional Annotation: AOP‑Based Implementation and Transaction Management Flow

The @Transactional annotation is Spring's declarative way to manage transactions, allowing developers to focus on business logic while the framework handles transaction start, commit, and rollback via AOP.

Spring defines a pointcut that matches methods annotated with @Transactional. During bean initialization, the AnnotationAwareAspectJAutoProxyCreator (a BeanPostProcessor) checks each bean; if the pointcut applies, it creates a proxy for that bean.

The proxy creation process involves the BeanFactoryTransactionAttributeSourceAdvisor, which acts as the advisor for transaction attributes. Spring evaluates whether the advisor applies to a bean via AopUtils#findAdvisorsThatCanApply, ultimately delegating to

AbstractFallbackTransactionAttributeSource#computeTransactionAttribute

to read the @Transactional metadata.

When a method is invoked on the proxy, the call is intercepted by DynamicAdvisedInterceptor#intercept. The interceptor builds a chain of interceptors, among which the TransactionInterceptor is responsible for the actual transaction handling.

@Override
public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
    // ... obtain target, advisors, and invoke the next interceptor ...
    Object retVal = methodProxy.invoke(target, args);
    return retVal;
}

The TransactionInterceptor#invoke method adapts the call to TransactionAspectSupport.invokeWithinTransaction, which determines the transaction attributes, selects a PlatformTransactionManager, and creates a TransactionInfo if needed.

@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() {
        @Override
        public Object proceedWithInvocation() throws Throwable {
            return invocation.proceed();
        }
    });
}

Inside invokeWithinTransaction, Spring either uses standard transaction demarcation (calling getTransaction, then commit or rollback) or, if the manager prefers callbacks, executes the method inside a TransactionCallback. The flow includes creating the transaction, invoking the target method, handling exceptions to trigger rollback, and finally committing the transaction.

protected Object invokeWithinTransaction(Method method, Class<?> targetClass, final InvocationCallback invocation) throws Throwable {
    TransactionAttribute txAttr = getTransactionAttributeSource().getTransactionAttribute(method, targetClass);
    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);
    }
}

By tracing these components, the article demonstrates how Spring translates the simple @Transactional declaration into a sophisticated AOP‑driven transaction management mechanism.

Finally, a visual summary (omitted here) aligns the hypothesized steps with the actual source‑code flow, confirming the complete lifecycle from annotation detection to transaction commit or rollback.