如何在数据库事务提交成功后进行异步操作

问题

业务场景

业务需求上经常会有一些边缘操作，比如主流程操作A：用户报名课程操作入库，边缘操作B：发送邮件或短信通知。

业务要求

• 操作A操作数据库失败后，事务回滚，那么操作B不能执行。

• 操作A执行成功后，操作B也必须执行成功

如何实现

• 普通的执行A，之后执行B，是可以满足要求1，对于要求2通常需要设计补偿的操作

• 一般边缘的操作，通常会设置成为异步的，以提升性能，比如发送MQ，业务系统负责事务成功后消息发送成功，然后接收系统负责保证通知成功完成

本文内容

如何在spring事务提交之后进行异步操作，这些异步操作必须得在该事务成功提交后才执行，回滚则不执行。

要点

• 如何在spring事务提交之后操作

• 如何把操作异步化

实现方案

使用TransactionSynchronizationManager在事务提交之后操作

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...");             }         }        );         ThreadLocalRandom random = ThreadLocalRandom.current();         if(random.nextInt() % 2 ==0){             throw new RuntimeException("test email transaction");         }         System.out.println("service end");     }

该方法就可以实现在事务提交之后进行操作

操作异步化

使用mq或线程池来进行异步，比如使用线程池：

private final ExecutorService executorService = Executors.newFixedThreadPool(5);     public void insert(TechBook techBook){         bookMapper.insert(techBook);   //        send after tx commit but is async         TransactionSynchronizationManager.registerSynchronization(new TransactionSynchronizationAdapter() {             @Override             public void afterCommit() {                 executorService.submit(new Runnable() {                     @Override                     public void run() {                         System.out.println("send email after transaction commit...");                         try {                             Thread.sleep(10*1000);                         } catch (InterruptedException e) {                             e.printStackTrace();                         }                         System.out.println("complete send email after transaction commit...");                     }                 });             }         }         );   //        async work but tx not work, execute even when tx is rollback //        asyncService.executeAfterTxComplete();           ThreadLocalRandom random = ThreadLocalRandom.current();         if(random.nextInt() % 2 ==0){             throw new RuntimeException("test email transaction");         }         System.out.println("service end");     }

封装以上两步

public interface AfterCommitExecutor extends Executor { }   import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.stereotype.Component; import org.springframework.transaction.support.TransactionSynchronizationAdapter; import org.springframework.transaction.support.TransactionSynchronizationManager;   import java.util.ArrayList; import java.util.List; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors;   @Component public class AfterCommitExecutorImpl extends TransactionSynchronizationAdapter implements AfterCommitExecutor {     private static final Logger LOGGER = LoggerFactory.getLogger(AfterCommitExecutorImpl.class);     private static final ThreadLocal<List<Runnable>> RUNNABLES = new ThreadLocal<List<Runnable>>();     private ExecutorService threadPool = Executors.newFixedThreadPool(5);       @Override     public void execute(Runnable runnable) {         LOGGER.info("Submitting new runnable {} to run after commit", runnable);         if (!TransactionSynchronizationManager.isSynchronizationActive()) {             LOGGER.info("Transaction synchronization is NOT ACTIVE. Executing right now runnable {}", runnable);             runnable.run();             return;         }         List<Runnable> threadRunnables = RUNNABLES.get();         if (threadRunnables == null) {             threadRunnables = new ArrayList<Runnable>();             RUNNABLES.set(threadRunnables);             TransactionSynchronizationManager.registerSynchronization(this);         }         threadRunnables.add(runnable);     }       @Override     public void afterCommit() {         List<Runnable> threadRunnables = RUNNABLES.get();         LOGGER.info("Transaction successfully committed, executing {} runnables", threadRunnables.size());         for (int i = 0; i < threadRunnables.size(); i++) {             Runnable runnable = threadRunnables.get(i);             LOGGER.info("Executing runnable {}", runnable);             try {                 threadPool.execute(runnable);             } catch (RuntimeException e) {                 LOGGER.error("Failed to execute runnable " + runnable, e);             }         }     }       @Override     public void afterCompletion(int status) {         LOGGER.info("Transaction completed with status {}", status == STATUS_COMMITTED ? "COMMITTED" : "ROLLED_BACK");         RUNNABLES.remove();     }   } public void insert(TechBook techBook){         bookMapper.insert(techBook);   //        send after tx commit but is async //        TransactionSynchronizationManager.registerSynchronization(new TransactionSynchronizationAdapter() { //            @Override //            public void afterCommit() { //                executorService.submit(new Runnable() { //                    @Override //                    public void run() { //                        System.out.println("send email after transaction commit..."); //                        try { //                            Thread.sleep(10*1000); //                        } catch (InterruptedException e) { //                            e.printStackTrace(); //                        } //                        System.out.println("complete send email after transaction commit..."); //                    } //                }); //            } //        } //        );           //send after tx commit and is async         afterCommitExecutor.execute(new Runnable() {             @Override             public void run() {                 try {                     Thread.sleep(5*1000);                 } catch (InterruptedException e) {                     e.printStackTrace();                 }                 System.out.println("send email after transactioin commit");             }         });   //        async work but tx not work, execute even when tx is rollback //        asyncService.executeAfterTxComplete();           ThreadLocalRandom random = ThreadLocalRandom.current();         if(random.nextInt() % 2 ==0){             throw new RuntimeException("test email transaction");         }         System.out.println("service end");     }

关于Spring的Async

spring为了方便应用使用线程池进行异步化，默认提供了@Async注解，可以整个app使用该线程池，而且只要一个@Async注解在方法上面即可，省去重复的submit操作。关于async要注意的几点：

1、async的配置

<context:component-scan base-package="com.yami" />    <!--配置@Async注解使用的线程池，这里的id随便命名，最后在task:annotation-driven executor= 指定上就可以-->     <task:executor id="myExecutor" pool-size="5"/>     <task:annotation-driven executor="myExecutor" />

这个必须配置在root context里头，而且web context不能扫描controller层外的注解，否则会覆盖掉。

<context:component-scan base-package="com.yami.web.controller"/> <mvc:annotation-driven/>

2、async的调用问题

async方法的调用，不能由同类方法内部调用，否则拦截不生效，这是spring默认的拦截问题，必须在其他类里头调用另一个类中带有async的注解方法，才能起到异步效果。

3、事务问题

async方法如果也开始事务的话，要注意事务传播以及事务开销的问题。而且在async方法里头使用如上的TransactionSynchronizationManager.registerSynchronization不起作用，值得注意。