一、背景

许多时候，我们期望在事务提交之后异步执行某些逻辑，调用外部系统，发送MQ，推送ES等等；当事务回滚时，异步操作也不执行，这些异步操作需要等待事务完成后才执行；比如出入库的事务执行完毕后，异步发送MQ给报表系统、ES等等

二、猜想

我们在项目中大多都是使用声明式事务(@Transactional注解) ，spring会基于动态代理机制对我们的业务方法进行增强，控制connection，从而达到事务的目的。那么我们能否在此找寻一些蛛丝马迹。我们来看下spring事务的相关核心类(装配流程不详细叙述)

(相关资料图)

TransactionInterceptor

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);  }}

TransactionAspectSupport(重点关注事务提交之后做了哪些事情，有哪些扩展点)

public abstract class TransactionAspectSupport implements BeanFactoryAware, InitializingBean { 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);   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);   }   PlatformTransactionManager ptm = asPlatformTransactionManager(tm);   final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);   if (txAttr == null || !(ptm instanceof CallbackPreferringPlatformTransactionManager)) {      // 创建事务，此处也会创建connection      TransactionInfo txInfo = createTransactionIfNecessary(ptm, txAttr, joinpointIdentification);      Object retVal;      try {         // 执行目标方法         retVal = invocation.proceedWithInvocation();      }      catch (Throwable ex) {         // 目标方法异常时处理         completeTransactionAfterThrowing(txInfo, ex);         throw ex;      }      finally { // 重置TransactionInfo ThreadLocal         cleanupTransactionInfo(txInfo);      }      if (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);         }      }  // 业务方法成功执行，提交事务(重点关注此处)，最终会调用AbstractPlatformTransactionManager#commit方法      commitTransactionAfterReturning(txInfo);      return retVal;   }   else {      final ThrowableHolder throwableHolder = new ThrowableHolder();      // It"s a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.      try {         Object result = ((CallbackPreferringPlatformTransactionManager) ptm).execute(txAttr, status -> {            TransactionInfo txInfo = prepareTransactionInfo(ptm, txAttr, joinpointIdentification, status);            try {               Object retVal = invocation.proceedWithInvocation();               if (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);            }         });         // Check result state: It might indicate a Throwable to rethrow.         if (throwableHolder.throwable != null) {            throw throwableHolder.throwable;         }         return result;      }      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;      }   }}}

AbstractPlatformTransactionManager

public final void commit(TransactionStatus status) throws TransactionException {   if (status.isCompleted()) {      throw new IllegalTransactionStateException(            "Transaction is already completed - do not call commit or rollback more than once per transaction");   }   DefaultTransactionStatus defStatus = (DefaultTransactionStatus) status;   if (defStatus.isLocalRollbackOnly()) {      if (defStatus.isDebug()) {         logger.debug("Transactional code has requested rollback");      }      processRollback(defStatus, false);      return;   }   if (!shouldCommitOnGlobalRollbackOnly() && defStatus.isGlobalRollbackOnly()) {      if (defStatus.isDebug()) {         logger.debug("Global transaction is marked as rollback-only but transactional code requested commit");      }      processRollback(defStatus, true);      return;   }   // 事务提交处理   processCommit(defStatus);}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 { // 在事务提交后触发(追踪到这里就离真相不远了)         triggerAfterCommit(status);      }      finally {         triggerAfterCompletion(status, TransactionSynchronization.STATUS_COMMITTED);      }   }   finally {      cleanupAfterCompletion(status);   }}

TransactionSynchronizationUtils

public abstract class TransactionSynchronizationUtils {  public static void triggerAfterCommit() {     // TransactionSynchronizationManager: 事务同步器管理     invokeAfterCommit(TransactionSynchronizationManager.getSynchronizations());  }  public static void invokeAfterCommit(@Nullable List<TransactionSynchronization> synchronizations) {     if (synchronizations != null) {        for (TransactionSynchronization synchronization : synchronizations) {   // 调用TransactionSynchronization#afterCommit方法，默认实现为空，留给子类扩展   // 那么我们想在事务提交之后做一些异步操作，实现此方法即可           synchronization.afterCommit();        }     }  }}

TransactionSynchronization

public interface TransactionSynchronization extends Flushable {   default void afterCommit() {}}

过程中我们发现TransactionSynchronizationManager、TransactionSynchronization、TransactionSynchronizationAdapter 等相关类涉及aop的整个流程，篇幅有限，在此不详细展开，当然我们的一些扩展也是离不开这些基础类的

三、实现

1、事务提交之后异步执行，我们需自定义synchronization.afterCommit，结合线程池一起使用，定义线程池TaskExecutor

@Beanpublic TaskExecutor taskExecutor() {    ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();    taskExecutor.setCorePoolSize(******);    taskExecutor.setMaxPoolSize(******);    taskExecutor.setKeepAliveSeconds(******);    taskExecutor.setQueueCapacity(******);    taskExecutor.setThreadNamePrefix(******);    taskExecutor.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardOldestPolicy());    taskExecutor.initialize();    return taskExecutor;}

2、定义AfterCommitExecutor接口

public interface AfterCommitExecutor extends Executor { }

3、定义AfterCommitExecutorImpl实现类，注意需继承TransactionSynchronizationAdapter类

import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.stereotype.Component;import org.springframework.core.NamedThreadLocal;import org.springframework.core.task.TaskExecutor;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.transaction.support.TransactionSynchronizationAdapter;import org.springframework.transaction.support.TransactionSynchronizationManager;import java.util.List;import java.util.ArrayList;@Componentpublic class AfterCommitExecutorImpl extends TransactionSynchronizationAdapter implements AfterCommitExecutor {    private static final Logger LOGGER = LoggerFactory.getLogger(AfterCommitExecutorImpl.class);    // 保存要运行的任务线程    private static final ThreadLocal<List<Runnable>> RUNNABLE_THREAD_LOCAL = new NamedThreadLocal<>("AfterCommitRunnable");    // 设置线程池    @Autowired    private TaskExecutor taskExecutor;    /**     * 异步执行     *     * @param runnable 异步线程     */    @Override    public void execute(Runnable runnable) {        LOGGER.info("Submitting new runnable {} to run after commit", runnable);        // 如果事务已经提交，马上进行异步处理        if (!TransactionSynchronizationManager.isSynchronizationActive()) {            LOGGER.info("Transaction synchronization is NOT ACTIVE. Executing right now runnable {}", runnable);            runnable.run();            return;        }        // 同一个事务的合并到一起处理(注意：没有初始化则初始化，并注册)        List<Runnable> threadRunnableList = RUNNABLE_THREAD_LOCAL.get();        if (null == threadRunnableList) {            threadRunnableList = new ArrayList<>();            RUNNABLE_THREAD_LOCAL.set(threadRunnableList);            TransactionSynchronizationManager.registerSynchronization(this);        }        threadRunnableList.add(runnable);    }    /**     * 监听到事务提交之后执行方法     */    @Override    public void afterCommit() {        List<Runnable> threadRunnableList = RUNNABLE_THREAD_LOCAL.get();        LOGGER.info("Transaction successfully committed, executing {} threadRunnable", threadRunnableList.size());        for (Runnable runnable : threadRunnableList) {            try {                taskExecutor.execute(runnable);            } catch (RuntimeException e) {                LOGGER.error("Failed to execute runnable " + runnable, e);            }        }    }    /**     * 事务提交/回滚执行     *     * @param status (STATUS_COMMITTED-0、STATUS_ROLLED_BACK-1、STATUS_UNKNOWN-2)     */    @Override    public void afterCompletion(int status) {        LOGGER.info("Transaction completed with status {}", status == STATUS_COMMITTED ? "COMMITTED" : "ROLLED_BACK");        RUNNABLE_THREAD_LOCAL.remove();    }}

4、使用

工具类封装好了，使用上那就很简便了；注入AfterCommitExecutor ，调用AfterCommitExecutor .execute(runnable)即可

四、总结

spring如此庞大，找准切入点，许多问题都是可以找到解决思路、或者方案；

你对spring了解多少......

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