Spring Transaction

Spring事务管理核心：

1.TransactionDefinition:定义一次事务传播行为，隔离级别，是否只读，本次事务名称

/**
	 * Return the propagation behavior.
	 * <p>Must return one of the <code>PROPAGATION_XXX</code> constants
	 * defined on {@link TransactionDefinition this interface}.
	 * @return the propagation behavior
	 * @see #PROPAGATION_REQUIRED
	 * @see org.springframework.transaction.support.TransactionSynchronizationManager#isActualTransactionActive()
	 */
	int getPropagationBehavior();

	/**
	 * Return the isolation level.
	 * <p>Must return one of the <code>ISOLATION_XXX</code> constants
	 * defined on {@link TransactionDefinition this interface}.
	 * <p>Only makes sense in combination with {@link #PROPAGATION_REQUIRED}
	 * or {@link #PROPAGATION_REQUIRES_NEW}.
	 * <p>Note that a transaction manager that does not support custom isolation levels
	 * will throw an exception when given any other level than {@link #ISOLATION_DEFAULT}.
	 * @return the isolation level
	 */
	int getIsolationLevel();

	/**
	 * Return the transaction timeout.
	 * <p>Must return a number of seconds, or {@link #TIMEOUT_DEFAULT}.
	 * <p>Only makes sense in combination with {@link #PROPAGATION_REQUIRED}
	 * or {@link #PROPAGATION_REQUIRES_NEW}.
	 * <p>Note that a transaction manager that does not support timeouts will throw
	 * an exception when given any other timeout than {@link #TIMEOUT_DEFAULT}.
	 * @return the transaction timeout
	 */
	int getTimeout();

	/**
	 * Return whether to optimize as a read-only transaction.
	 * <p>The read-only flag applies to any transaction context, whether
	 * backed by an actual resource transaction
	 * ({@link #PROPAGATION_REQUIRED}/{@link #PROPAGATION_REQUIRES_NEW}) or
	 * operating non-transactionally at the resource level
	 * ({@link #PROPAGATION_SUPPORTS}). In the latter case, the flag will
	 * only apply to managed resources within the application, such as a
	 * Hibernate <code>Session</code>.
<<	 * <p>This just serves as a hint for the actual transaction subsystem;
	 * it will <i>not necessarily</i> cause failure of write access attempts.
	 * A transaction manager which cannot interpret the read-only hint will
	 * <i>not</i> throw an exception when asked for a read-only transaction.
	 * @return <code>true</code> if the transaction is to be optimized as read-only 
	 * @see org.springframework.transaction.support.TransactionSynchronization#beforeCommit(boolean)
	 * @see org.springframework.transaction.support.TransactionSynchronizationManager#isCurrentTransactionReadOnly()
         * 最终会调用connection.setReadOnly方法，然后不能执行更新操作
	 */
	boolean isReadOnly();

	/**
	 * Return the name of this transaction. Can be <code>null</code>.
	 * <p>This will be used as the transaction name to be shown in a
	 * transaction monitor, if applicable (for example, WebLogic's).
	 * <p>In case of Spring's declarative transactions, the exposed name will be
	 * the <code>fully-qualified class name + "." + method name</code> (by default).
	 * @return the name of this transaction
	 * @see org.springframework.transaction.interceptor.TransactionAspectSupport
	 * @see org.springframework.transaction.support.TransactionSynchronizationManager#getCurrentTransactionName()
	 */
	String getName();

 

2.TransactionStatus: 事务状态

/**
	 * Return whether the present transaction is new (else participating
	 * in an existing transaction, or potentially not running in an
	 * actual transaction in the first place).
         * 是不是一个新的事务，即是不是一个独立的事务 
	 */
	boolean isNewTransaction();

	/**
	 * Return whether this transaction internally carries a savepoint,
	 * that is, has been created as nested transaction based on a savepoint.
	 * <p>This method is mainly here for diagnostic purposes, alongside
	 * {@link #isNewTransaction()}. For programmatic handling of custom
	 * savepoints, use SavepointManager's operations.
	 * @see #isNewTransaction()
	 * @see #createSavepoint
	 * @see #rollbackToSavepoint(Object)
	 * @see #releaseSavepoint(Object)
         * 是否有保存点
	 */
	boolean hasSavepoint();

	/**
	 * Set the transaction rollback-only. This instructs the transaction manager
	 * that the only possible outcome of the transaction may be a rollback, as
	 * alternative to throwing an exception which would in turn trigger a rollback.
	 * <p>This is mainly intended for transactions managed by
	 * {@link org.springframework.transaction.support.TransactionTemplate} or
	 * {@link org.springframework.transaction.interceptor.TransactionInterceptor},
	 * where the actual commit/rollback decision is made by the container.
	 * @see org.springframework.transaction.support.TransactionCallback#doInTransaction
	 * @see org.springframework.transaction.interceptor.TransactionAttribute#rollbackOn
	 * 将该事务设置成回滚，事务结束时会回滚
         */
	void setRollbackOnly();

	/**
	 * Return whether the transaction has been marked as rollback-only
	 * (either by the application or by the transaction infrastructure).
         * 事务是不是设置了只允许回滚的属性
	 */
	boolean isRollbackOnly();

	/**
	 * Flush the underlying session to the datastore, if applicable:
	 * for example, all affected Hibernate/JPA sessions.
	 */
	void flush();

	/**
	 * Return whether this transaction is completed, that is,
	 * whether it has already been committed or rolled back.
	 * @see PlatformTransactionManager#commit
	 * @see PlatformTransactionManager#rollback
         * 事务是否完成？
	 */
	boolean isCompleted();

 默认的实现DefaultTransactionStatus

ublic class DefaultTransactionStatus extends AbstractTransactionStatus {

	private final Object transaction;  //事务对象

	private final boolean newTransaction; //是不是一个新事务即独立的事务

	private final boolean newSynchronization;//?

	private final boolean readOnly;//是不是只读事务

	private final boolean debug; //是不是日志级别为debug

	private final Object suspendedResources; //挂起的事务资源
        /**如果已经存在A事务，方法B的事务传播级别为REQUIRED_NEW，则会将A事务的信息放在B事务/*的suspendedResources中，同时将B事务的newTransaction设置为true，保证这是一个新的事务，然后
/* B事务会获得到一个新的连接
*/

 

3. PlatformTransactionManager

public interface PlatformTransactionManager {

	/**
	 * 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 TransactionDefinition instance (can be <code>null</code> 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(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</code> 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</code> 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;

}

 

AbstractPlatformTransactionManager

/**
	 * Always activate transaction synchronization, even for "empty" transactions
	 * that result from PROPAGATION_SUPPORTS with no existing backend transaction.
	 * @see org.springframework.transaction.TransactionDefinition#PROPAGATION_SUPPORTS
	 * @see org.springframework.transaction.TransactionDefinition#PROPAGATION_NOT_SUPPORTED
	 * @see org.springframework.transaction.TransactionDefinition#PROPAGATION_NEVER
	 */
	public static final int SYNCHRONIZATION_ALWAYS = 0;

	/**
	 * Activate transaction synchronization only for actual transactions,
	 * that is, not for empty ones that result from PROPAGATION_SUPPORTS with
	 * no existing backend transaction.
	 * @see org.springframework.transaction.TransactionDefinition#PROPAGATION_REQUIRED
	 * @see org.springframework.transaction.TransactionDefinition#PROPAGATION_MANDATORY
	 * @see org.springframework.transaction.TransactionDefinition#PROPAGATION_REQUIRES_NEW
	 */
	public static final int SYNCHRONIZATION_ON_ACTUAL_TRANSACTION = 1;

	/**
	 * Never active transaction synchronization, not even for actual transactions.
	 */
	public static final int SYNCHRONIZATION_NEVER = 2;


	/** Constants instance for AbstractPlatformTransactionManager */
	private static final Constants constants = new Constants(AbstractPlatformTransactionManager.class);


	protected transient Log logger = LogFactory.getLog(getClass());

	private int transactionSynchronization = SYNCHRONIZATION_ALWAYS;

	private int defaultTimeout = TransactionDefinition.TIMEOUT_DEFAULT;

	private boolean nestedTransactionAllowed = false;

	private boolean validateExistingTransaction = false;

	private boolean globalRollbackOnParticipationFailure = true;

	private boolean failEarlyOnGlobalRollbackOnly = false;

	private boolean rollbackOnCommitFailure = false;

 

4. TransactionSynchronizationManager:资源管理，在同一线程的任一地方均可获取

	private static final Log logger = LogFactory.getLog(TransactionSynchronizationManager.class);

	private static final ThreadLocal<Map<Object, Object>> resources =
			new NamedThreadLocal<Map<Object, Object>>("Transactional resources");

	private static final ThreadLocal<Set<TransactionSynchronization>> synchronizations =
			new NamedThreadLocal<Set<TransactionSynchronization>>("Transaction synchronizations");

	private static final ThreadLocal<String> currentTransactionName =
			new NamedThreadLocal<String>("Current transaction name");

	private static final ThreadLocal<Boolean> currentTransactionReadOnly =
			new NamedThreadLocal<Boolean>("Current transaction read-only status");

	private static final ThreadLocal<Integer> currentTransactionIsolationLevel =
			new NamedThreadLocal<Integer>("Current transaction isolation level");

	private static final ThreadLocal<Boolean> actualTransactionActive =
			new NamedThreadLocal<Boolean>("Actual transaction active");


	//-------------------------------------------------------------------------
	// Management of transaction-associated resource handles
	//-------------------------------------------------------------------------