@Transactional 源码解析
- 1.springboot 下@Transactional使用方式
- 2.spring是怎么处理事务的
- 2.1 创建事务
- 2.2 调用业务方法
- 2.3 清除事务
- 2.4 提交或者回滚事务
1.springboot 下@Transactional使用方式
在springboot框架下，事务管理只要在实现类方法上增加@Transactional这个注解就可以了。
@Transactional
@Override
public int insertMapiInterfaceCallConfig(InterfaceCallConfigDomain mapiInterfaceCallConfig) {
return mapiInterfaceCallConfigMapper.insertMapiInterfaceCallConfig(mapiInterfaceCallConfig);
}2.spring是怎么处理事务的
spring 是通过aop 的方式来管理事务的，具体来看如下代码
事务aop处理类TransactionInterceptor
package org.springframework.transaction.interceptor;
@SuppressWarnings("serial")
public class TransactionInterceptor extends TransactionAspectSupport implements MethodInterceptor, Serializable {
@Override
@Nullable
public Object invoke(MethodInvocation invocation) throws Throwable {
// Work out the target class: may be {@code null}.
// The TransactionAttributeSource should be passed the target class
// as well as the method, which may be from an interface.
Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);
// Adapt to TransactionAspectSupport's invokeWithinTransaction...
return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);
}
}调用TransactionAspectSupport的invokeWithinTransaction
分三种情况
- 响应式编程事务处理
- 命令式编程事务处理
- 没有事务的方法处理
如下代码：
public abstract class TransactionAspectSupport implements BeanFactoryAware, InitializingBean {
@Nullable
protected Object invokeWithinTransaction(Method method, @Nullable Class<?> targetClass,
final InvocationCallback invocation) throws Throwable {
// If the transaction attribute is null, the method is non-transactional.
TransactionAttributeSource tas = getTransactionAttributeSource();
final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
final TransactionManager tm = determineTransactionManager(txAttr);
#1. 响应式编程事务处理
if (this.reactiveAdapterRegistry != null && tm instanceof ReactiveTransactionManager) {
ReactiveTransactionSupport txSupport = this.transactionSupportCache.computeIfAbsent(method, key -> {
if (KotlinDetector.isKotlinType(method.getDeclaringClass()) && KotlinDelegate.isSuspend(method)) {
throw new TransactionUsageException(
"Unsupported annotated transaction on suspending function detected: " + method +
". Use TransactionalOperator.transactional extensions instead.");
}
ReactiveAdapter adapter = this.reactiveAdapterRegistry.getAdapter(method.getReturnType());
if (adapter == null) {
throw new IllegalStateException("Cannot apply reactive transaction to non-reactive return type: " +
method.getReturnType());
}
return new ReactiveTransactionSupport(adapter);
});
return txSupport.invokeWithinTransaction(
method, targetClass, invocation, txAttr, (ReactiveTransactionManager) tm);
}
# 2. 命令式编程事务处理
PlatformTransactionManager ptm = asPlatformTransactionManager(tm);
final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);
if (txAttr == null || !(ptm instanceof CallbackPreferringPlatformTransactionManager)) {
// Standard transaction demarcation with getTransaction and commit/rollback calls.
TransactionInfo txInfo = createTransactionIfNecessary(ptm, txAttr, joinpointIdentification);
Object retVal;
try {
// This is an around advice: Invoke the next interceptor in the chain.
// This will normally result in a target object being invoked.
retVal = invocation.proceedWithInvocation();
}
catch (Throwable ex) {
// target invocation exception
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
}
finally {
cleanupTransactionInfo(txInfo);
}
if (retVal != null && vavrPresent && VavrDelegate.isVavrTry(retVal)) {
// Set rollback-only in case of Vavr failure matching our rollback rules...
TransactionStatus status = txInfo.getTransactionStatus();
if (status != null && txAttr != null) {
retVal = VavrDelegate.evaluateTryFailure(retVal, txAttr, status);
}
}
commitTransactionAfterReturning(txInfo);
return retVal;
}
else {
# 3.没有事务的方法处理
Object result;
final ThrowableHolder throwableHolder = new ThrowableHolder();
// It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.
try {
result = ((CallbackPreferringPlatformTransactionManager) ptm).execute(txAttr, status -> {
TransactionInfo txInfo = prepareTransactionInfo(ptm, txAttr, joinpointIdentification, status);
try {
Object retVal = invocation.proceedWithInvocation();
if (retVal != null && vavrPresent && VavrDelegate.isVavrTry(retVal)) {
// Set rollback-only in case of Vavr failure matching our rollback rules...
retVal = VavrDelegate.evaluateTryFailure(retVal, txAttr, status);
}
return retVal;
}
catch (Throwable ex) {
if (txAttr.rollbackOn(ex)) {
// A RuntimeException: will lead to a rollback.
if (ex instanceof RuntimeException) {
throw (RuntimeException) ex;
}
else {
throw new ThrowableHolderException(ex);
}
}
else {
// A normal return value: will lead to a commit.
throwableHolder.throwable = ex;
return null;
}
}
finally {
cleanupTransactionInfo(txInfo);
}
});
}
catch (ThrowableHolderException ex) {
throw ex.getCause();
}
catch (TransactionSystemException ex2) {
if (throwableHolder.throwable != null) {
logger.error("Application exception overridden by commit exception", throwableHolder.throwable);
ex2.initApplicationException(throwableHolder.throwable);
}
throw ex2;
}
catch (Throwable ex2) {
if (throwableHolder.throwable != null) {
logger.error("Application exception overridden by commit exception", throwableHolder.throwable);
}
throw ex2;
}
// Check result state: It might indicate a Throwable to rethrow.
if (throwableHolder.throwable != null) {
throw throwableHolder.throwable;
}
return result;
}
}
}我们主要分析第二种情况，主要分为4个步骤：
2.1 创建事务
主要路径代码
创建事务开始
protected TransactionInfo createTransactionIfNecessary(@Nullable PlatformTransactionManager tm,
@Nullable TransactionAttribute txAttr, final String joinpointIdentification) {
// If no name specified, apply method identification as transaction name.
if (txAttr != null && txAttr.getName() == null) {
txAttr = new DelegatingTransactionAttribute(txAttr) {
@Override
public String getName() {
return joinpointIdentification;
}
};
}
TransactionStatus status = null;
if (txAttr != null) {
if (tm != null) {
status = tm.getTransaction(txAttr);
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Skipping transactional joinpoint [" + joinpointIdentification +
"] because no transaction manager has been configured");
}
}
}
return prepareTransactionInfo(tm, txAttr, joinpointIdentification, status);
}从以下源码中可以看到，创建事务之前看下能不能从当前线程绑定的resources中取得，我举例的场景是第一次调用事务方法，所以肯定拿不到。从这边也可以看出事务是与线程绑定的，后面我还会分析是怎么绑定的。 ThreadLocal<Map<Object, Object>> resources 这边又看到 ThreadLocal的影子了。
public abstract class TransactionSynchronizationManager {
private static final Log logger = LogFactory.getLog(TransactionSynchronizationManager.class);
private static final ThreadLocal<Map<Object, Object>> resources =
new NamedThreadLocal<>("Transactional resources");
/**
* Actually check the value of the resource that is bound for the given key.
*/
@Nullable
private static Object doGetResource(Object actualKey) {
Map<Object, Object> map = resources.get();
if (map == null) {
return null;
}
Object value = map.get(actualKey);
// Transparently remove ResourceHolder that was marked as void...
if (value instanceof ResourceHolder && ((ResourceHolder) value).isVoid()) {
map.remove(actualKey);
// Remove entire ThreadLocal if empty...
if (map.isEmpty()) {
resources.remove();
}
value = null;
}
return value;
}
创建事务开始了…,
public abstract class AbstractPlatformTransactionManager implements PlatformTransactionManager, Serializable {
private TransactionStatus startTransaction(TransactionDefinition definition, Object transaction,
boolean debugEnabled, @Nullable SuspendedResourcesHolder suspendedResources) {
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
DefaultTransactionStatus status = newTransactionStatus(
definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
doBegin(transaction, definition);
prepareSynchronization(status, definition);
return status;
}我们进入doBegin方法看看…,（1）处先从数据源对象中拿连接对接设置到ConnectionHolder中。（2）处判断当前是不是自动提交模式，如果是，就把它设置为非自动提交。（3）处把当前connection 绑定到线程上。（前面分析到在创建之前会从当前线程拿，这边就是赋值的过程）
public class DataSourceTransactionManager extends AbstractPlatformTransactionManager
implements ResourceTransactionManager, InitializingBean {
@Override
protected void doBegin(Object transaction, TransactionDefinition definition) {
DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
Connection con = null;
try {
if (!txObject.hasConnectionHolder() ||
txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
（1）#从数据源里拿数据库连接
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).
if (con.getAutoCommit()) {
txObject.setMustRestoreAutoCommit(true);
if (logger.isDebugEnabled()) {
logger.debug("Switching JDBC Connection [" + con + "] to manual commit");
}
#（2）判断是否自动提交，如果是自动提交就改成手动提交。
con.setAutoCommit(false);
}
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.
#（3）处把当前connection 绑定到线程上
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);
}
}再展开下上一步的（2）处，是如何设置为手动提交的，如下代码：
实际执行的就是这句（SET autocommit=0），所以跟我们平时在控制台写语句是一样的
2.2 调用业务方法
调用业务方法比较简单
2.3 清除事务
清除事务就是从当前线程解绑，把旧的事务设置到当前线程。注：我的例子中因为是第一次创建事务，所以旧的事务为null
finally {
cleanupTransactionInfo(txInfo);
}
private void restoreThreadLocalStatus() {
// Use stack to restore old transaction TransactionInfo.
// Will be null if none was set.
transactionInfoHolder.set(this.oldTransactionInfo);
}2.4 提交或者回滚事务
业务执行方法如果没有异常的话，就执行正常的提交。如下（1）处理，就是最终的提交事务语句。
@Override
public void commit() throws SQLException {
synchronized (getConnectionMutex()) {
checkClosed();
try {
if (this.connectionLifecycleInterceptors != null) {
IterateBlock<ConnectionLifecycleInterceptor> iter = new IterateBlock<ConnectionLifecycleInterceptor>(
this.connectionLifecycleInterceptors.iterator()) {
@Override
void forEach(ConnectionLifecycleInterceptor each) throws SQLException {
if (!each.commit()) {
this.stopIterating = true;
}
}
};
iter.doForAll();
if (!iter.fullIteration()) {
return;
}
}
if (this.session.getServerSession().isAutoCommit()) {
throw SQLError.createSQLException(Messages.getString("Connection.3"), getExceptionInterceptor());
}
if (this.useLocalTransactionState.getValue()) {
if (!this.session.getServerSession().inTransactionOnServer()) {
return; // effectively a no-op
}
}
#（1），就是最终的提交事务语句
this.session.execSQL(null, "commit", -1, null, false, this.nullStatementResultSetFactory, null, false);
} catch (SQLException sqlException) {
if (MysqlErrorNumbers.SQL_STATE_COMMUNICATION_LINK_FAILURE.equals(sqlException.getSQLState())) {
throw SQLError.createSQLException(Messages.getString("Connection.4"), MysqlErrorNumbers.SQL_STATE_TRANSACTION_RESOLUTION_UNKNOWN,
getExceptionInterceptor());
}
throw sqlException;
} finally {
this.session.setNeedsPing(this.reconnectAtTxEnd.getValue());
}
}
return;
}
本文章为转载内容，我们尊重原作者对文章享有的著作权。如有内容错误或侵权问题，欢迎原作者联系我们进行内容更正或删除文章。
