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本文次要钻研一下 spring 的 TransactionSynchronizationAdapter
示例代码
public void insert(TechBook techBook){bookMapper.insert(techBook);
// send after tx commit but is async
TransactionSynchronizationManager.registerSynchronization(new TransactionSynchronizationAdapter() {
@Override
public void afterCommit() {System.out.println("send email after transaction commit...");
}
}
);
System.out.println("service end");
}
应用 TransactionSynchronizationManager.registerSynchronization 注册了一个 TransactionSynchronizationAdapter,在其 afterCommit 办法也就是事务提交胜利之后执行一些额定逻辑
TransactionSynchronizationAdapter
org/springframework/transaction/support/TransactionSynchronizationAdapter.java
public abstract class TransactionSynchronizationAdapter implements TransactionSynchronization, Ordered {
@Override
public int getOrder() {return Ordered.LOWEST_PRECEDENCE;}
@Override
public void suspend() {}
@Override
public void resume() {}
@Override
public void flush() {}
@Override
public void beforeCommit(boolean readOnly) { }
@Override
public void beforeCompletion() {}
@Override
public void afterCommit() {}
@Override
public void afterCompletion(int status) {}}
TransactionSynchronizationAdapter 是个抽象类,申明实现 TransactionSynchronization 及 Ordered 接口
TransactionSynchronization
org/springframework/transaction/support/TransactionSynchronization.java
/**
* Invoked after transaction commit. Can perform further operations right
* <i>after</i> the main transaction has <i>successfully</i> committed.
* <p>Can e.g. commit further operations that are supposed to follow on a successful
* commit of the main transaction, like confirmation messages or emails.
* <p><b>NOTE:</b> The transaction will have been committed already, but the
* transactional resources might still be active and accessible. As a consequence,
* any data access code triggered at this point will still "participate" in the
* original transaction, allowing to perform some cleanup (with no commit following
* anymore!), unless it explicitly declares that it needs to run in a separate
* transaction. Hence: <b>Use {@code PROPAGATION_REQUIRES_NEW} for any
* transactional operation that is called from here.</b>
* @throws RuntimeException in case of errors; will be <b>propagated to the caller</b>
* (note: do not throw TransactionException subclasses here!)
*/
default void afterCommit() {}
留神这里正文阐明了异样不会被捕捉,而且倡议不在这里抛出 TransactionException 的子类;另外对于 afterCommit 有数据库相干操作的倡议应用 PROPAGATION_REQUIRES_NEW 这个事务流传级别,不然 afterCommit 的操作可能不会失效
registerSynchronization
org/springframework/transaction/support/TransactionSynchronizationManager.java
private static final ThreadLocal<Set<TransactionSynchronization>> synchronizations =
new NamedThreadLocal<>("Transaction synchronizations");
/**
* Register a new transaction synchronization for the current thread.
* Typically called by resource management code.
* <p>Note that synchronizations can implement the
* {@link org.springframework.core.Ordered} interface.
* They will be executed in an order according to their order value (if any).
* @param synchronization the synchronization object to register
* @throws IllegalStateException if transaction synchronization is not active
* @see org.springframework.core.Ordered
*/
public static void registerSynchronization(TransactionSynchronization synchronization)
throws IllegalStateException {Assert.notNull(synchronization, "TransactionSynchronization must not be null");
Set<TransactionSynchronization> synchs = synchronizations.get();
if (synchs == null) {throw new IllegalStateException("Transaction synchronization is not active");
}
synchs.add(synchronization);
}
TransactionSynchronizationManager 的 registerSynchronization 办法会把 TransactionSynchronization 注册到以后线程的 synchronizations
processCommit
org/springframework/transaction/support/AbstractPlatformTransactionManager.java
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);
}
}
private void triggerAfterCommit(DefaultTransactionStatus status) {if (status.isNewSynchronization()) {if (status.isDebug()) {logger.trace("Triggering afterCommit synchronization");
}
TransactionSynchronizationUtils.triggerAfterCommit();}
}
AbstractPlatformTransactionManager 的 processCommit 办法,在提交胜利之后触发 triggerAfterCommit,这里调用了 TransactionSynchronizationUtils.triggerAfterCommit(),留神这里没有 try catch,阐明 triggerAfterCommit 的异样最终会抛给调用方
triggerAfterCommit
org/springframework/transaction/support/TransactionSynchronizationUtils.java
public static void triggerAfterCommit() {invokeAfterCommit(TransactionSynchronizationManager.getSynchronizations());
}
public static void invokeAfterCommit(@Nullable List<TransactionSynchronization> synchronizations) {if (synchronizations != null) {for (TransactionSynchronization synchronization : synchronizations) {synchronization.afterCommit();
}
}
}
这里遍历 synchronizations 执行 afterCommit 办法,如果其中有一个有异样抛出则中断
小结
应用 TransactionSynchronizationManager.registerSynchronization 能够在以后线程的事务注册一个 TransactionSynchronizationAdapter,能够在 afterCommit 办法也就是事务提交胜利之后执行一些额定逻辑;留神这里抛出的异样不影响事务提交,然而异样不会被 catch 须要由调用方解决,对于 afterCommit 有数据库相干操作的倡议应用 PROPAGATION_REQUIRES_NEW 这个事务流传级别,不然 afterCommit 的 db 操作可能不会失效。
在事务提交之后做一些事件可能不须要 TransactionSynchronizationManager.registerSynchronization 这种形式也能实现,也就是须要额定一层来调用事务操作,有异样会抛出,没有异样则执行事务提交之后的事件,前提就是事务回滚异样不能被吞掉,不然外层调用可能认为事务胜利了
还有一种形式就是应用 TransactionalEventListener,这种形式比 TransactionSynchronizationManager.registerSynchronization 更为优雅一些
doc
- 如何在数据库事务提交胜利后进行异步操作
- Spring 事务 aftercommit 原理及实际