如何在数据库事务提交成功后进行异步操作
jopen
9年前
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
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操作A操作数据库失败后，事务回滚，那么操作B不能执行。
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操作A执行成功后，操作B也必须执行成功
如何实现
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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
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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
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如何在spring事务提交之后操作
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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。
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