TransactionSynchronizationManager事务同步管理器
TransactionSynchronizationManager
- 业务场景
- 源码解读
- 简单demo
- 参考文章
业务场景
我们在事务执行前后可能需要做一些额外的操作这个时候我们就需要用到TransactionSynchronizationManager去注入一个TransactionSynchronization事务同步器，然后重写TransactionSynchronization或者其子类的beforeCommit()或者afterCommit()方法，写入我们需要执行的业务。
源码解读
public abstract class TransactionSynchronizationManager {
private static final Log logger = LogFactory.getLog(TransactionSynchronizationManager.class);
//Connection对象
private static final ThreadLocal> resources =
new NamedThreadLocal<>("Transactional resources");
//事务同步器，是Spring交由程序员进行扩展的代码，每个线程可以注册N个事务同步器。
private static final ThreadLocal> synchronizations =
new NamedThreadLocal<>("Transaction synchronizations");
//当前事务名称
private static final ThreadLocal currentTransactionName =
new NamedThreadLocal<>("Current transaction name");
//当前事务是否只读
private static final ThreadLocal currentTransactionReadOnly =
new NamedThreadLocal<>("Current transaction read-only status");
//隔离级别
private static final ThreadLocal currentTransactionIsolationLevel =
new NamedThreadLocal<>("Current transaction isolation level");
//事务是否开启
private static final ThreadLocal actualTransactionActive =
new NamedThreadLocal<>("Actual transaction active");
//-------------------------------------------------------------------------
// Management of transaction-associated resource handles
//-------------------------------------------------------------------------
/**
* Return all resources that are bound to the current thread.
* Mainly for debugging purposes. Resource managers should always invoke
* {@code hasResource} for a specific resource key that they are interested in.
* @return a Map with resource keys (usually the resource factory) and resource
* values (usually the active resource object), or an empty Map if there are
* currently no resources bound
* @see #hasResource
*/
//获取连接
public static Map getResourceMap() {
Map map = resources.get();
return (map != null ? Collections.unmodifiableMap(map) : Collections.emptyMap());
}
/**
* Check if there is a resource for the given key bound to the current thread.
* @param key the key to check (usually the resource factory)
* @return if there is a value bound to the current thread
* @see ResourceTransactionManager#getResourceFactory()
*/
//指定key是否有Resource
public static boolean hasResource(Object key) {
//返回实际底层actualKey
Object actualKey = TransactionSynchronizationUtils.unwrapResou//frceIfNecessary(key);
Object value = doGetResource(actualKey);
return (value != null);
}
/**
* Retrieve a resource for the given key that is bound to the current thread.
* @param key the key to check (usually the resource factory)
* @return a value bound to the current thread (usually the active
* resource object), or {@code null} if none
* @see ResourceTransactionManager#getResourceFactory()
*/
@Nullable
//获取指定key的Resource
public static Object getResource(Object key) {
Object actualKey = TransactionSynchronizationUtils.unwrapResourceIfNecessary(key);
Object value = doGetResource(actualKey);
if (value != null && logger.isTraceEnabled()) {
logger.trace("Retrieved value [" + value + "] for key [" + actualKey + "] bound to thread [" +
Thread.currentThread().getName() + "]");
}
return value;
}
/**
* Actually check the value of the resource that is bound for the given key.
*/
@Nullable
private static Object doGetResource(Object actualKey) {
Map map = resources.get();
if (map == null) {
return null;
}
Object value = map.get(actualKey);
// Transparently remove ResourceHolder that was marked as void...
//删除void ResourceHolder
if (value instanceof ResourceHolder && ((ResourceHolder) value).isVoid()) {
map.remove(actualKey);
// Remove entire ThreadLocal if empty...
if (map.isEmpty()) {
resources.remove();
}
value = null;
}
return value;
}
/**
* Bind the given resource for the given key to the current thread.
* @param key the key to bind the value to (usually the resource factory)
* @param value the value to bind (usually the active resource object)
* @throws IllegalStateException if there is already a value bound to the thread
* @see ResourceTransactionManager#getResourceFactory()
* 将Resource连接信息绑定到当前线程
*/
public static void bindResource(Object key, Object value) throws IllegalStateException {
Object actualKey = TransactionSynchronizationUtils.unwrapResourceIfNecessary(key);
Assert.notNull(value, "Value must not be null");
Map 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() + "]");
}
}
/**
* Unbind a resource for the given key from the current thread.
* @param key the key to unbind (usually the resource factory)
* @return the previously bound value (usually the active resource object)
* @throws IllegalStateException if there is no value bound to the thread
* @see ResourceTransactionManager#getResourceFactory()
*/
//resource解绑指定key
public static Object unbindResource(Object key) throws IllegalStateException {
Object actualKey = TransactionSynchronizationUtils.unwrapResourceIfNecessary(key);
Object value = doUnbindResource(actualKey);
if (value == null) {
throw new IllegalStateException(
"No value for key [" + actualKey + "] bound to thread [" + Thread.currentThread().getName() + "]");
}
return value;
}
/**
* Unbind a resource for the given key from the current thread.
* @param key the key to unbind (usually the resource factory)
* @return the previously bound value, or {@code null} if none bound
*/
@Nullable
public static Object unbindResourceIfPossible(Object key) {
Object actualKey = TransactionSynchronizationUtils.unwrapResourceIfNecessary(key);
return doUnbindResource(actualKey);
}
/**
* Actually remove the value of the resource that is bound for the given key.
*/
@Nullable
private static Object doUnbindResource(Object actualKey) {
Map map = resources.get();
if (map == null) {
return null;
}
Object value = map.remove(actualKey);
// Remove entire ThreadLocal if empty...
if (map.isEmpty()) {
resources.remove();
}
// Transparently suppress a ResourceHolder that was marked as void...
if (value instanceof ResourceHolder && ((ResourceHolder) value).isVoid()) {
value = null;
}
if (value != null && logger.isTraceEnabled()) {
logger.trace("Removed value [" + value + "] for key [" + actualKey + "] from thread [" +
Thread.currentThread().getName() + "]");
}
return value;
}
//-------------------------------------------------------------------------
// Management of transaction synchronizations
//-------------------------------------------------------------------------
/**
* Return if transaction synchronization is active for the current thread.
* Can be called before register to avoid unnecessary instance creation.
* @see #registerSynchronization
*/
//当前线程的事务同步是否处于活动状态。
//在注册之前调用，以避免不必要的实例创建。
public static boolean isSynchronizationActive() {
return (synchronizations.get() != null);
}
/**
* Activate transaction synchronization for the current thread.
* Called by a transaction manager on transaction begin.
* @throws IllegalStateException if synchronization is already active
*/
//初始化事务同步器，如果当前事务同步器存在则抛异常
public static void initSynchronization() throws IllegalStateException {
if (isSynchronizationActive()) {
throw new IllegalStateException("Cannot activate transaction synchronization - already active");
}
logger.trace("Initializing transaction synchronization");
synchronizations.set(new LinkedHashSet<>());
}
/**
* Register a new transaction synchronization for the current thread.
* Typically called by resource management code.
* 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
*/
//注册同步器
public static void registerSynchronization(TransactionSynchronization synchronization)
throws IllegalStateException {
Assert.notNull(synchronization, "TransactionSynchronization must not be null");
if (!isSynchronizationActive()) {
throw new IllegalStateException("Transaction synchronization is not active");
}
synchronizations.get().add(synchronization);
}
/**
* Return an unmodifiable snapshot list of all registered synchronizations
* for the current thread.
* @return unmodifiable List of TransactionSynchronization instances
* @throws IllegalStateException if synchronization is not active
* @see TransactionSynchronization
*/
//获取所有同步器列表
public static List getSynchronizations() throws IllegalStateException {
Set synchs = synchronizations.get();
if (synchs == null) {
throw new IllegalStateException("Transaction synchronization is not active");
}
// Return unmodifiable snapshot, to avoid ConcurrentModificationExceptions
// while iterating and invoking synchronization callbacks that in turn
// might register further synchronizations.
if (synchs.isEmpty()) {
return Collections.emptyList();
}
else {
// Sort lazily here, not in registerSynchronization.
List sortedSynchs = new ArrayList<>(synchs);
//根据注解
AnnotationAwareOrderComparator.sort(sortedSynchs);
return Collections.unmodifiableList(sortedSynchs);
}
}
/**
* Deactivate transaction synchronization for the current thread.
* Called by the transaction manager on transaction cleanup.
* @throws IllegalStateException if synchronization is not active
*/
//清空所有事务同步器
public static void clearSynchronization() throws IllegalStateException {
if (!isSynchronizationActive()) {
throw new IllegalStateException("Cannot deactivate transaction synchronization - not active");
}
logger.trace("Clearing transaction synchronization");
synchronizations.remove();
}
//-------------------------------------------------------------------------
// Exposure of transaction characteristics
//-------------------------------------------------------------------------
/**
* Expose the name of the current transaction, if any.
* Called by the transaction manager on transaction begin and on cleanup.
* @param name the name of the transaction, or {@code null} to reset it
* @see org.springframework.transaction.TransactionDefinition#getName()
*/
public static void setCurrentTransactionName(@Nullable String name) {
currentTransactionName.set(name);
}
/**
* Return the name of the current transaction, or {@code null} if none set.
* To be called by resource management code for optimizations per use case,
* for example to optimize fetch strategies for specific named transactions.
* @see org.springframework.transaction.TransactionDefinition#getName()
*/
@Nullable
public static String getCurrentTransactionName() {
return currentTransactionName.get();
}
/**
* Expose a read-only flag for the current transaction.
* Called by the transaction manager on transaction begin and on cleanup.
* @param readOnly {@code true} to mark the current transaction
* as read-only; {@code false} to reset such a read-only marker
* @see org.springframework.transaction.TransactionDefinition#isReadOnly()
*/
public static void setCurrentTransactionReadOnly(boolean readOnly) {
currentTransactionReadOnly.set(readOnly ? Boolean.TRUE : null);
}
/**
* Return whether the current transaction is marked as read-only.
* To be called by resource management code when preparing a newly
* created resource (for example, a Hibernate Session).
* Note that transaction synchronizations receive the read-only flag
* as argument for the {@code beforeCommit} callback, to be able
* to suppress change detection on commit. The present method is meant
* to be used for earlier read-only checks, for example to set the
* flush mode of a Hibernate Session to "FlushMode.NEVER" upfront.
* @see org.springframework.transaction.TransactionDefinition#isReadOnly()
* @see TransactionSynchronization#beforeCommit(boolean)
*/
public static boolean isCurrentTransactionReadOnly() {
return (currentTransactionReadOnly.get() != null);
}
/**
* Expose an isolation level for the current transaction.
* Called by the transaction manager on transaction begin and on cleanup.
* @param isolationLevel the isolation level to expose, according to the
* JDBC Connection constants (equivalent to the corresponding Spring
* TransactionDefinition constants), or {@code null} to reset it
* @see java.sql.Connection#TRANSACTION_READ_UNCOMMITTED
* @see java.sql.Connection#TRANSACTION_READ_COMMITTED
* @see java.sql.Connection#TRANSACTION_REPEATABLE_READ
* @see java.sql.Connection#TRANSACTION_SERIALIZABLE
* @see org.springframework.transaction.TransactionDefinition#ISOLATION_READ_UNCOMMITTED
* @see org.springframework.transaction.TransactionDefinition#ISOLATION_READ_COMMITTED
* @see org.springframework.transaction.TransactionDefinition#ISOLATION_REPEATABLE_READ
* @see org.springframework.transaction.TransactionDefinition#ISOLATION_SERIALIZABLE
* @see org.springframework.transaction.TransactionDefinition#getIsolationLevel()
* 设置事务隔离级别
* 1.READ_UNCOMMITTED
* 2.READ_COMMITTED
* 4.REPEATABLE_READ
* 8.SERIALIZABLE
*/
public static void setCurrentTransactionIsolationLevel(@Nullable Integer isolationLevel) {
currentTransactionIsolationLevel.set(isolationLevel);
}
/**
* Return the isolation level for the current transaction, if any.
* To be called by resource management code when preparing a newly
* created resource (for example, a JDBC Connection).
* @return the currently exposed isolation level, according to the
* JDBC Connection constants (equivalent to the corresponding Spring
* TransactionDefinition constants), or {@code null} if none
* @see java.sql.Connection#TRANSACTION_READ_UNCOMMITTED
* @see java.sql.Connection#TRANSACTION_READ_COMMITTED
* @see java.sql.Connection#TRANSACTION_REPEATABLE_READ
* @see java.sql.Connection#TRANSACTION_SERIALIZABLE
* @see org.springframework.transaction.TransactionDefinition#ISOLATION_READ_UNCOMMITTED
* @see org.springframework.transaction.TransactionDefinition#ISOLATION_READ_COMMITTED
* @see org.springframework.transaction.TransactionDefinition#ISOLATION_REPEATABLE_READ
* @see org.springframework.transaction.TransactionDefinition#ISOLATION_SERIALIZABLE
* @see org.springframework.transaction.TransactionDefinition#getIsolationLevel()
*/
@Nullable
public static Integer getCurrentTransactionIsolationLevel() {
return currentTransactionIsolationLevel.get();
}
/**
* Expose whether there currently is an actual transaction active.
* Called by the transaction manager on transaction begin and on cleanup.
* @param active {@code true} to mark the current thread as being associated
* with an actual transaction; {@code false} to reset that marker
*设置事务状态是否开启
*/
public static void setActualTransactionActive(boolean active) {
actualTransactionActive.set(active ? Boolean.TRUE : null);
}
/**
* Return whether there currently is an actual transaction active.
* This indicates whether the current thread is associated with an actual
* transaction rather than just with active transaction synchronization.
*
To be called by resource management code that wants to discriminate
* between active transaction synchronization (with or without backing
* resource transaction; also on PROPAGATION_SUPPORTS) and an actual
* transaction being active (with backing resource transaction;
* on PROPAGATION_REQUIRED, PROPAGATION_REQUIRES_NEW, etc).
* @see #isSynchronizationActive()
*/
public static boolean isActualTransactionActive() {
return (actualTransactionActive.get() != null);
}
/**
* Clear the entire transaction synchronization state for the current thread:
* registered synchronizations as well as the various transaction characteristics.
* @see #clearSynchronization()
* @see #setCurrentTransactionName
* @see #setCurrentTransactionReadOnly
* @see #setCurrentTransactionIsolationLevel
* @see #setActualTransactionActive
*清空所有信息
*/
public static void clear() {
synchronizations.remove();
currentTransactionName.remove();
currentTransactionReadOnly.remove();
currentTransactionIsolationLevel.remove();
actualTransactionActive.remove();
}
}
简单demo
@Transactional(rollbackFor = Exception.class)
public void test() {
...
// 事务执行成功后调取
TransactionSynchronizationManager.registerSynchronization(new TransactionSynchronizationAdapter() {
@Override
public void afterCommit() {
System.out.println("事务执行成功后调取");
}
});
}
参考文章
- AnnotationAwareOrderComparator.sort 排序规则
- Spring进阶篇（7）-TransactionSynchronizationManager(事务监听)