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스프링을 사용하다보면 @Transactional을 굉장히 많이 사용한다.
에러가 발생하면 transaction을 rollback 시켜주기 때문에 사용한다라고는 알고 있지만, 어떠한 방식으로 동작하는지는 제대로 알아보지 않은 것 같다.
우선 블로그들과 spring framework의 github를 참고했다.
@Transactional을 사용하면 interceptor가 중간에 가져와서 invokeWithinTransaction가 실행되도록 한다.
안에서 작성된 코드는 이정도 되는 것 같다.
protected @Nullable 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();
final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
final TransactionManager tm = determineTransactionManager(txAttr, targetClass);
if (this.reactiveAdapterRegistry != null && tm instanceof ReactiveTransactionManager rtm) {
boolean isSuspendingFunction = KotlinDetector.isSuspendingFunction(method);
boolean hasSuspendingFlowReturnType = isSuspendingFunction &&
COROUTINES_FLOW_CLASS_NAME.equals(new MethodParameter(method, -1).getParameterType().getName());
ReactiveTransactionSupport txSupport = this.transactionSupportCache.computeIfAbsent(method, key -> {
Class<?> reactiveType =
(isSuspendingFunction ? (hasSuspendingFlowReturnType ? Flux.class : Mono.class) : method.getReturnType());
ReactiveAdapter adapter = this.reactiveAdapterRegistry.getAdapter(reactiveType);
if (adapter == null) {
throw new IllegalStateException("Cannot apply reactive transaction to non-reactive return type [" +
method.getReturnType() + "] with specified transaction manager: " + tm);
}
return new ReactiveTransactionSupport(adapter);
});
return txSupport.invokeWithinTransaction(method, targetClass, invocation, txAttr, rtm);
}
PlatformTransactionManager ptm = asPlatformTransactionManager(tm);
final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);
if (txAttr == null || !(ptm instanceof CallbackPreferringPlatformTransactionManager cpptm)) {
// Standard transaction demarcation with getTransaction and commit/rollback calls.
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.
retVal = invocation.proceedWithInvocation();
}
catch (Throwable ex) {
// target invocation exception
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
}
finally {
cleanupTransactionInfo(txInfo);
}
if (retVal != null && txAttr != null) {
TransactionStatus status = txInfo.getTransactionStatus();
if (status != null) {
if (retVal instanceof Future<?> future && future.isDone()) {
try {
future.get();
}
catch (ExecutionException ex) {
Throwable cause = ex.getCause();
Assert.state(cause != null, "Cause must not be null");
if (txAttr.rollbackOn(cause)) {
status.setRollbackOnly();
}
}
catch (InterruptedException ex) {
Thread.currentThread().interrupt();
}
}
else if (vavrPresent && VavrDelegate.isVavrTry(retVal)) {
// Set rollback-only in case of Vavr failure matching our rollback rules...
retVal = VavrDelegate.evaluateTryFailure(retVal, txAttr, status);
}
}
}
commitTransactionAfterReturning(txInfo);
return retVal;
}
else {
Object result;
final ThrowableHolder throwableHolder = new ThrowableHolder();
// It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.
try {
result = cpptm.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 runtimeException) {
throw runtimeException;
}
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;
}
}
우선 트랜잭션의 속성과 매니저를 가져온다.
TransactionAttributeSource tas = getTransactionAttributeSource();
TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
TransactionManager tm = determineTransactionManager(txAttr, targetClass);
특별한 설정이 없다면, 트랜잭션을 처리한다.
PlatformTransactionManager ptm = asPlatformTransactionManager(tm);
...
if (txAttr == null || !(ptm instanceof CallbackPreferringPlatformTransactionManager cpptm)) {
}
아래의 메서드로 트랜잭션이 진행된다.
- 트랜잭션 시작 (createTransactionIfNecessary)
- 비즈니스 로직 실행 (invocation.proceedWithInvocation())
- 예외 발생 시 롤백 (completeTransactionAfterThrowing)
- 정상 종료 시 커밋 (commitTransactionAfterReturning)
아래의 메서드로 에러 발생시 롤백이 예약된다.
status.setRollbackOnly();
만약, 해당 트랜잭션이 중첩이 되어 있다면
호출한 트랜잭션으로 전파된다.
if (throwableHolder.throwable != null) {
throw throwableHolder.throwable;
}
return result;
간단하게 정리하자면
- Spring이 트랜잭션 어노테이션이 붙은 메서드를 감지
- 그 메서드를 프록시(Proxy) 객체로 감쌉니다
- 실제 메서드를 호출할 때, 프록시가 트랜잭션 관련 로직을 앞뒤로 끼워 넣습니다
이런식으로 트랜잭션이 처리된다.
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