트랜잭션 작동 코드

TransactionManager 클라이언트 - TransactionTemplate

1. 트랜잭션 매니저에게 트랜잭션 오브젝트 요청
2. 디비 계층 로직 수행
3. 런타임 예외 발생시 롤백
4. 커밋

	@Override
	@Nullable
	public <T> T execute(TransactionCallback<T> action) throws TransactionException {
		Assert.state(this.transactionManager != null, "No PlatformTransactionManager set");

		if (this.transactionManager instanceof CallbackPreferringPlatformTransactionManager cpptm) {
			return cpptm.execute(this, action);
		}
		else {
			TransactionStatus status = this.transactionManager.getTransaction(this);
			T result;
			try {
				result = action.doInTransaction(status);
			}
			catch (RuntimeException | Error ex) {
				// Transactional code threw application exception -> rollback
				rollbackOnException(status, ex);
				throw ex;
			}
			catch (Throwable ex) {
				// Transactional code threw unexpected exception -> rollback
				rollbackOnException(status, ex);
				throw new UndeclaredThrowableException(ex, "TransactionCallback threw undeclared checked exception");
			}
			this.transactionManager.commit(status);
			return result;
		}
	}

PlatformTransactionManager

PlatformTransactionManager 의 기본 기능

• getTransaction
• commit
• rollback

public interface PlatformTransactionManager extends TransactionManager {

> 	/**
	 * Return a currently active transaction or create a new one, according to
	 * the specified propagation behavior.
	 * <p>Note that parameters like isolation level or timeout will only be applied
	 * to new transactions, and thus be ignored when participating in active ones.
	 * <p>Furthermore, not all transaction definition settings will be supported
	 * by every transaction manager: A proper transaction manager implementation
	 * should throw an exception when unsupported settings are encountered.
	 * <p>An exception to the above rule is the read-only flag, which should be
	 * ignored if no explicit read-only mode is supported. Essentially, the
	 * read-only flag is just a hint for potential optimization.
	 * @param definition the TransactionDefinition instance (can be {@code null} for defaults),
	 * describing propagation behavior, isolation level, timeout etc.
	 * @return transaction status object representing the new or current transaction
	 * @throws TransactionException in case of lookup, creation, or system errors
	 * @throws IllegalTransactionStateException if the given transaction definition
	 * cannot be executed (for example, if a currently active transaction is in
	 * conflict with the specified propagation behavior)
	 * @see TransactionDefinition#getPropagationBehavior
	 * @see TransactionDefinition#getIsolationLevel
	 * @see TransactionDefinition#getTimeout
	 * @see TransactionDefinition#isReadOnly
	 */
	TransactionStatus getTransaction(@Nullable TransactionDefinition definition)
			throws TransactionException;

	/**
	 * Commit the given transaction, with regard to its status. If the transaction
	 * has been marked rollback-only programmatically, perform a rollback.
	 * <p>If the transaction wasn't a new one, omit the commit for proper
	 * participation in the surrounding transaction. If a previous transaction
	 * has been suspended to be able to create a new one, resume the previous
	 * transaction after committing the new one.
	 * <p>Note that when the commit call completes, no matter if normally or
	 * throwing an exception, the transaction must be fully completed and
	 * cleaned up. No rollback call should be expected in such a case.
	 * <p>If this method throws an exception other than a TransactionException,
	 * then some before-commit error caused the commit attempt to fail. For
	 * example, an O/R Mapping tool might have tried to flush changes to the
	 * database right before commit, with the resulting DataAccessException
	 * causing the transaction to fail. The original exception will be
	 * propagated to the caller of this commit method in such a case.
	 * @param status object returned by the {@code getTransaction} method
	 * @throws UnexpectedRollbackException in case of an unexpected rollback
	 * that the transaction coordinator initiated
	 * @throws HeuristicCompletionException in case of a transaction failure
	 * caused by a heuristic decision on the side of the transaction coordinator
	 * @throws TransactionSystemException in case of commit or system errors
	 * (typically caused by fundamental resource failures)
	 * @throws IllegalTransactionStateException if the given transaction
	 * is already completed (that is, committed or rolled back)
	 * @see TransactionStatus#setRollbackOnly
	 */
	void commit(TransactionStatus status) throws TransactionException;

	/**
	 * Perform a rollback of the given transaction.
	 * <p>If the transaction wasn't a new one, just set it rollback-only for proper
	 * participation in the surrounding transaction. If a previous transaction
	 * has been suspended to be able to create a new one, resume the previous
	 * transaction after rolling back the new one.
	 * <p><b>Do not call rollback on a transaction if commit threw an exception.</b>
	 * The transaction will already have been completed and cleaned up when commit
	 * returns, even in case of a commit exception. Consequently, a rollback call
	 * after commit failure will lead to an IllegalTransactionStateException.
	 * @param status object returned by the {@code getTransaction} method
	 * @throws TransactionSystemException in case of rollback or system errors
	 * (typically caused by fundamental resource failures)
	 * @throws IllegalTransactionStateException if the given transaction
	 * is already completed (that is, committed or rolled back)
	 */
	void rollback(TransactionStatus status) throws TransactionException;

}

getTransaction()

AbstractPlatformTransactionManager.getTransaction() 내부 코드
1. doGetTransaction() 호출
2. transaction 전파 설정에 따른 로직 수행
3. TransactionStatus 생성, 트랜잭션 동기화 매니저 동기화 요청

 public class DefaultTransactionStatus extends AbstractTransactionStatus {

	@Nullable
	private final Object transaction;

	private final boolean newTransaction;

	private final boolean newSynchronization;

	private final boolean readOnly;

	private final boolean debug;

transaction – underlying transaction object that can hold state for the internal transaction implementation
트랜잭션 구현에 따른 트랜잭션 상태가 존재함

commit()

AbstractPlatformTransactionManager.getTransaction() 내부 코드

1. commit 하기 전 rollback flag 확인, true 면 커밋하지 않고 롤백한다.
2. commit 수행

	/**
	 * This implementation of commit handles participating in existing
	 * transactions and programmatic rollback requests.
	 * Delegates to {@code isRollbackOnly}, {@code doCommit}
	 * and {@code rollback}.
	 * @see org.springframework.transaction.TransactionStatus#isRollbackOnly()
	 * @see #doCommit
	 * @see #rollback
	 */
	@Override
	public final void commit(TransactionStatus status) throws TransactionException {
		if (status.isCompleted()) {
			throw new IllegalTransactionStateException(
					"Transaction is already completed - do not call commit or rollback more than once per transaction");
		}

		DefaultTransactionStatus defStatus = (DefaultTransactionStatus) status;
		if (defStatus.isLocalRollbackOnly()) {
			if (defStatus.isDebug()) {
				logger.debug("Transactional code has requested rollback");
			}
			processRollback(defStatus, false);
			return;
		}

		if (!shouldCommitOnGlobalRollbackOnly() && defStatus.isGlobalRollbackOnly()) {
			if (defStatus.isDebug()) {
				logger.debug("Global transaction is marked as rollback-only but transactional code requested commit");
			}
			processRollback(defStatus, true);
			return;
		}

		processCommit(defStatus);
	}

processCommit(defStatus)

	/**
	 * Process an actual commit.
	 * Rollback-only flags have already been checked and applied.
	 * @param status object representing the transaction
	 * @throws TransactionException in case of commit failure
	 */
	private void processCommit(DefaultTransactionStatus status) throws TransactionException {
		try {
			boolean beforeCompletionInvoked = false;

			try {
				boolean unexpectedRollback = false;
				prepareForCommit(status);
				triggerBeforeCommit(status);
				triggerBeforeCompletion(status);
				beforeCompletionInvoked = true;

				if (status.hasSavepoint()) {
					if (status.isDebug()) {
						logger.debug("Releasing transaction savepoint");
					}
					unexpectedRollback = status.isGlobalRollbackOnly();
					status.releaseHeldSavepoint();
				}
				else if (status.isNewTransaction()) {
					if (status.isDebug()) {
						logger.debug("Initiating transaction commit");
					}
					unexpectedRollback = status.isGlobalRollbackOnly();
					doCommit(status);
				}
				else if (isFailEarlyOnGlobalRollbackOnly()) {
					unexpectedRollback = status.isGlobalRollbackOnly();
				}

				// Throw UnexpectedRollbackException if we have a global rollback-only
				// marker but still didn't get a corresponding exception from commit.
				if (unexpectedRollback) {
					throw new UnexpectedRollbackException(
							"Transaction silently rolled back because it has been marked as rollback-only");
				}
			}
			catch (UnexpectedRollbackException ex) {
				// can only be caused by doCommit
				triggerAfterCompletion(status, TransactionSynchronization.STATUS_ROLLED_BACK);
				throw ex;
			}
			catch (TransactionException ex) {
				// can only be caused by doCommit
				if (isRollbackOnCommitFailure()) {
					doRollbackOnCommitException(status, ex);
				}
				else {
					triggerAfterCompletion(status, TransactionSynchronization.STATUS_UNKNOWN);
				}
				throw ex;
			}
			catch (RuntimeException | Error ex) {
				if (!beforeCompletionInvoked) {
					triggerBeforeCompletion(status);
				}
				doRollbackOnCommitException(status, ex);
				throw ex;
			}

			// Trigger afterCommit callbacks, with an exception thrown there
			// propagated to callers but the transaction still considered as committed.
			try {
				triggerAfterCommit(status);
			}
			finally {
				triggerAfterCompletion(status, TransactionSynchronization.STATUS_COMMITTED);
			}

		}
		finally {
			cleanupAfterCompletion(status);
		}
	}

---

토비 스프링 7장

자바 언어의 변화와 스프링

1. 어노테이션의 메타정보 활용

• 어노테이션은 자바 코드가 실행되는 데 직접 참여하지 못한다.
• 어노테이션은 리플렉션 API 를 이용해 어노테이션의 메타정보를 조회하고, 어노테이션 내에 설정된 값을 가져와 참고한다.
• 어노테이션의 활용이 늘어난 이유는 어플리케이션 핵심 로직을 담은 자바 코드와 이를 지원하는 IoC 방식의 프레임워크, 그리고 프레임워크가 참조하는 메타정보라는 세 가지로 구성하는 방식에 잘 어울린다.
• 어노테이션의 장점은
  • 메타정보를 XML과 달리 외부 파일이 아니라 자바 코드 일부로 존재한다.
  • 어노테이션을 선언하면 클래스의 다양한 부가정보를 얻어낼 수 있다.
• 단점은
  • 수정하면 빌드를 다시 해야된다.

2. 정책과 관례를 이용한 프로그래밍

• 어노테이션을 사용ㅇ하면 동작 내용을 기술하는 대신 코드 없이 미리 약속한 규칙 또는 관례를 따라서 프로그램이 동작하도록 프로그래밍을 할 수 있다.
• 그러나 메타정보를 보고 프로그램이 어떻게 동작할 지 이해해야 하는 부담이 있다.

스프링 3.1부터는 DI원리와 다양한 패턴을 빈과 DI 설정정보를 담은 자바 코드와 어노테이션에 적용하기 시작했다.