今天我们来看一下事务管理器TransactionManager。
DataSourceTransactionManager的介绍
上一篇文章我们说了TransactionAspectSupport类，其中获取到事务管理器是DataSourceTransactionManager
所以我们今天的主角就是DataSourceTransactionManager
其实DataSourceTransactionManager最重要的接口是PlatformTransactionManager
public interface PlatformTransactionManager extends TransactionManager {
//创建事务
TransactionStatus getTransaction(@Nullable TransactionDefinition definition)
throws TransactionException;
//提交事务
void commit(TransactionStatus status) throws TransactionException;
//事务回滚
void rollback(TransactionStatus status) throws TransactionException;
}
主要的是实现还是要看AbstractPlatformTransactionManager
首先是getTransaction
默认情况下的传播行为是PROPAGATION_REQUIRED
doBegin的抽象方法主要实现在DataSourceTransactionManager
@Override
protected void doBegin(Object transaction, TransactionDefinition definition) {
DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
Connection con = null;
try {
if (!txObject.hasConnectionHolder() ||
txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
Connection newCon = obtainDataSource().getConnection();
if (logger.isDebugEnabled()) {
logger.debug("Acquired Connection [" + newCon + "] for JDBC transaction");
}
txObject.setConnectionHolder(new ConnectionHolder(newCon), true);
}
txObject.getConnectionHolder().setSynchronizedWithTransaction(true);
con = txObject.getConnectionHolder().getConnection();
Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
txObject.setPreviousIsolationLevel(previousIsolationLevel);
txObject.setReadOnly(definition.isReadOnly());
// Switch to manual commit if necessary. This is very expensive in some JDBC drivers,
// so we don't want to do it unnecessarily (for example if we've explicitly
// configured the connection pool to set it already).
//如果datasource默认情况下是自动提交事务，我们需要将自动改为手动
if (con.getAutoCommit()) {
txObject.setMustRestoreAutoCommit(true);
if (logger.isDebugEnabled()) {
logger.debug("Switching JDBC Connection [" + con + "] to manual commit");
}
con.setAutoCommit(false);
}
//执行开启事务的命令
prepareTransactionalConnection(con, definition);
txObject.getConnectionHolder().setTransactionActive(true);
int timeout = determineTimeout(definition);
if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
txObject.getConnectionHolder().setTimeoutInSeconds(timeout);
}
// Bind the connection holder to the thread.
//如果是新的连接，就在事务同步管理器中将datasource和connectionholder进行绑定
if (txObject.isNewConnectionHolder()) {
TransactionSynchronizationManager.bindResource(obtainDataSource(), txObject.getConnectionHolder());
}
}
catch (Throwable ex) {
if (txObject.isNewConnectionHolder()) {
DataSourceUtils.releaseConnection(con, obtainDataSource());
txObject.setConnectionHolder(null, false);
}
throw new CannotCreateTransactionException("Could not open JDBC Connection for transaction", ex);
}
}
TransactionSynchronizationManager.bindResource里面的逻辑很简单
public static void bindResource(Object key, Object value) throws IllegalStateException {
Object actualKey = TransactionSynchronizationUtils.unwrapResourceIfNecessary(key);
Assert.notNull(value, "Value must not be null");
Map<Object, Object> map = resources.get();
// set ThreadLocal Map if none found
if (map == null) {
map = new HashMap<>();
resources.set(map);
}
Object oldValue = map.put(actualKey, value);
// Transparently suppress a ResourceHolder that was marked as void...
if (oldValue instanceof ResourceHolder && ((ResourceHolder) oldValue).isVoid()) {
oldValue = null;
}
if (oldValue != null) {
throw new IllegalStateException("Already value [" + oldValue + "] for key [" +
actualKey + "] bound to thread [" + Thread.currentThread().getName() + "]");
}
if (logger.isTraceEnabled()) {
logger.trace("Bound value [" + value + "] for key [" + actualKey + "] to thread [" +
Thread.currentThread().getName() + "]");
}
}
commit提交事务的逻辑
这里我们主要看提交的方法，回滚方法自己感兴趣可以看一下；
private void processCommit(DefaultTransactionStatus status) throws TransactionException {
try {
boolean beforeCompletionInvoked = false;
try {
boolean unexpectedRollback = false;
//钩子函数
prepareForCommit(status);
//钩子函数
triggerBeforeCommit(status);
//钩子函数
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();
//提交事务的逻辑
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.
//钩子函数
try {
triggerAfterCommit(status);
}
finally {
//钩子函数
triggerAfterCompletion(status, TransactionSynchronization.STATUS_COMMITTED);
}
}
finally {
//钩子函数
cleanupAfterCompletion(status);
}
}
钩子函数感兴趣的可以研究一下，还是很有用的
- triggerBeforeCompletion(status);
- triggerBeforeCommit(status);
- prepareForCommit(status);
- triggerAfterCommit(status);
- triggerAfterCompletion(status, TransactionSynchronization.STATUS_COMMITTED);
- cleanupAfterCompletion(status);
docommit()是主要的提交事务逻辑，它是个抽象方法，这里的实现还是在DataSourceTransactionManager中，里面的逻辑很简单，我们就不做描述了。
最后我们来看一下回滚的方法
rollback的逻辑
老规矩，还是看processRollback方法
private void processRollback(DefaultTransactionStatus status, boolean unexpected) {
try {
boolean unexpectedRollback = unexpected;
try {
triggerBeforeCompletion(status);
if (status.hasSavepoint()) {
if (status.isDebug()) {
logger.debug("Rolling back transaction to savepoint");
}
status.rollbackToHeldSavepoint();
}
else if (status.isNewTransaction()) {
if (status.isDebug()) {
logger.debug("Initiating transaction rollback");
}
doRollback(status);
}
else {
// Participating in larger transaction
if (status.hasTransaction()) {
if (status.isLocalRollbackOnly() || isGlobalRollbackOnParticipationFailure()) {
if (status.isDebug()) {
logger.debug("Participating transaction failed - marking existing transaction as rollback-only");
}
doSetRollbackOnly(status);
}
else {
if (status.isDebug()) {
logger.debug("Participating transaction failed - letting transaction originator decide on rollback");
}
}
}
else {
logger.debug("Should roll back transaction but cannot - no transaction available");
}
// Unexpected rollback only matters here if we're asked to fail early
if (!isFailEarlyOnGlobalRollbackOnly()) {
unexpectedRollback = false;
}
}
}
catch (RuntimeException | Error ex) {
triggerAfterCompletion(status, TransactionSynchronization.STATUS_UNKNOWN);
throw ex;
}
triggerAfterCompletion(status, TransactionSynchronization.STATUS_ROLLED_BACK);
// Raise UnexpectedRollbackException if we had a global rollback-only marker
if (unexpectedRollback) {
throw new UnexpectedRollbackException(
"Transaction rolled back because it has been marked as rollback-only");
}
}
finally {
cleanupAfterCompletion(status);
}
}
doRollback的逻辑也很简单
