上一篇文章springboot中事务的源码分析（二）中我们在commit方法中提到了一些钩子函数，今天我们挑几个重点的讲一下
我们以triggerAfterCommit方法为例：
里面的逻辑很简单，重点就是
TransactionSynchronizationUtils.triggerAfterCommit();我们先来看一下TransactionSynchronizationUtils这个类，这个类是个抽象类，从代码上看，里面都的钩子方法都用了TransactionSynchronizationManager类。
事务同步管理器TransactionSynchronizationManager类是我们要说明的重点。
public abstract class TransactionSynchronizationUtils {
private static final Log logger = LogFactory.getLog(TransactionSynchronizationUtils.class);
private static final boolean aopAvailable = ClassUtils.isPresent(
"org.springframework.aop.scope.ScopedObject", TransactionSynchronizationUtils.class.getClassLoader());
/**
* Check whether the given resource transaction managers refers to the given
* (underlying) resource factory.
* @see ResourceTransactionManager#getResourceFactory()
* @see org.springframework.core.InfrastructureProxy#getWrappedObject()
*/
public static boolean sameResourceFactory(ResourceTransactionManager tm, Object resourceFactory) {
return unwrapResourceIfNecessary(tm.getResourceFactory()).equals(unwrapResourceIfNecessary(resourceFactory));
}
/**
* Unwrap the given resource handle if necessary; otherwise return
* the given handle as-is.
* @see org.springframework.core.InfrastructureProxy#getWrappedObject()
*/
static Object unwrapResourceIfNecessary(Object resource) {
Assert.notNull(resource, "Resource must not be null");
Object resourceRef = resource;
// unwrap infrastructure proxy
if (resourceRef instanceof InfrastructureProxy) {
resourceRef = ((InfrastructureProxy) resourceRef).getWrappedObject();
}
if (aopAvailable) {
// now unwrap scoped proxy
resourceRef = ScopedProxyUnwrapper.unwrapIfNecessary(resourceRef);
}
return resourceRef;
}
/**
* Trigger {@code flush} callbacks on all currently registered synchronizations.
* @throws RuntimeException if thrown by a {@code flush} callback
* @see TransactionSynchronization#flush()
*/
public static void triggerFlush() {
for (TransactionSynchronization synchronization : TransactionSynchronizationManager.getSynchronizations()) {
synchronization.flush();
}
}
/**
* Trigger {@code beforeCommit} callbacks on all currently registered synchronizations.
* @param readOnly whether the transaction is defined as read-only transaction
* @throws RuntimeException if thrown by a {@code beforeCommit} callback
* @see TransactionSynchronization#beforeCommit(boolean)
*/
public static void triggerBeforeCommit(boolean readOnly) {
for (TransactionSynchronization synchronization : TransactionSynchronizationManager.getSynchronizations()) {
synchronization.beforeCommit(readOnly);
}
}
/**
* Trigger {@code beforeCompletion} callbacks on all currently registered synchronizations.
* @see TransactionSynchronization#beforeCompletion()
*/
public static void triggerBeforeCompletion() {
for (TransactionSynchronization synchronization : TransactionSynchronizationManager.getSynchronizations()) {
try {
synchronization.beforeCompletion();
}
catch (Throwable tsex) {
logger.error("TransactionSynchronization.beforeCompletion threw exception", tsex);
}
}
}
/**
* Trigger {@code afterCommit} callbacks on all currently registered synchronizations.
* @throws RuntimeException if thrown by a {@code afterCommit} callback
* @see TransactionSynchronizationManager#getSynchronizations()
* @see TransactionSynchronization#afterCommit()
*/
public static void triggerAfterCommit() {
invokeAfterCommit(TransactionSynchronizationManager.getSynchronizations());
}
/**
* Actually invoke the {@code afterCommit} methods of the
* given Spring TransactionSynchronization objects.
* @param synchronizations a List of TransactionSynchronization objects
* @see TransactionSynchronization#afterCommit()
*/
public static void invokeAfterCommit(@Nullable List<TransactionSynchronization> synchronizations) {
if (synchronizations != null) {
for (TransactionSynchronization synchronization : synchronizations) {
synchronization.afterCommit();
}
}
}
/**
* Trigger {@code afterCompletion} callbacks on all currently registered synchronizations.
* @param completionStatus the completion status according to the
* constants in the TransactionSynchronization interface
* @see TransactionSynchronizationManager#getSynchronizations()
* @see TransactionSynchronization#afterCompletion(int)
* @see TransactionSynchronization#STATUS_COMMITTED
* @see TransactionSynchronization#STATUS_ROLLED_BACK
* @see TransactionSynchronization#STATUS_UNKNOWN
*/
public static void triggerAfterCompletion(int completionStatus) {
List<TransactionSynchronization> synchronizations = TransactionSynchronizationManager.getSynchronizations();
invokeAfterCompletion(synchronizations, completionStatus);
}
/**
* Actually invoke the {@code afterCompletion} methods of the
* given Spring TransactionSynchronization objects.
* @param synchronizations a List of TransactionSynchronization objects
* @param completionStatus the completion status according to the
* constants in the TransactionSynchronization interface
* @see TransactionSynchronization#afterCompletion(int)
* @see TransactionSynchronization#STATUS_COMMITTED
* @see TransactionSynchronization#STATUS_ROLLED_BACK
* @see TransactionSynchronization#STATUS_UNKNOWN
*/
public static void invokeAfterCompletion(@Nullable List<TransactionSynchronization> synchronizations,
int completionStatus) {
if (synchronizations != null) {
for (TransactionSynchronization synchronization : synchronizations) {
try {
synchronization.afterCompletion(completionStatus);
}
catch (Throwable tsex) {
logger.error("TransactionSynchronization.afterCompletion threw exception", tsex);
}
}
}
}
/**
* Inner class to avoid hard-coded dependency on AOP module.
*/
private static class ScopedProxyUnwrapper {
public static Object unwrapIfNecessary(Object resource) {
if (resource instanceof ScopedObject) {
return ((ScopedObject) resource).getTargetObject();
}
else {
return resource;
}
}
}
}
我们还是根据这个triggerAfterCommit方法作为一个逻辑线来看，在上述代码我们可以看到triggerAfterCommit方法-> invokeAfterCommit方法，底层用到了事务同步管理器
最后执行的还是TransactionSynchronization接口的afterCommit方法，其他的钩子函数与其逻辑大概相似。
这个TransactionSynchronization是个接口，大家是不是很好奇，哪里会用到这个接口呢，又是怎么注册到事务同步管理器里的呢？那我们先看一下哪些类实现了这个接口
用过mybatis的应该都知道SqlSessionTemplate吧，
上述的逻辑上getSqlSession-->registerSessionHolder方法：
TransactionSynchronizationManager
.registerSynchronization(new SqlSessionSynchronization(holder, sessionFactory));
看一看SqlSessionSynchronization
终于看到了曙光，TransactionSynchronizationAdapter继承了TransactionSynchronization接口。
下篇文章我们来讲述一下TransactionSynchronizationAdapter怎么用？什么场景下用？
