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

对于第二步来说，如果这类方法比较多的话，则写起来重复性太多，因而，抽象出来如下：
这里改造了azagorneanu的代码:

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。