场景

在业务中，经常需要在执行数据库操作后（事务提交完成），发送消息或事件来异步调用其他组件执行相应的业务操作。
比如： 用户注册成功后，发送激活码或激活邮件，如果用户保存后就执行异步操作发送激活码或激活邮件，但是前面用户保存后发生异常，数据库进行回滚，用户实际没有注册成功，但用户收到激活码或激活邮件。此时，我们就迫切要求数据库事务完成后再执行异步操作。

需求

在成功修改数据库后，向Rabbitmq发送一条消息

解决方案

1.使用TransactionSynchronizationManage 控制事务

TransactionSynchronization 该类中有方法可以控制业务在提交事务后执行。

service的代码

 public boolean updateById(Hotel hotel) {
        logger.info("----- into service -----");

        //修改DB的数据
        hotelMapper.updateById(hotel);

        //事务提交后再执行
        TransactionSynchronizationManager.registerSynchronization(new TransactionSynchronization() {
            @Override
            public void afterCommit() {
                //成功修改DB的数据后，向Rabbitmq发消息
                rabbitTemplate.convertAndSend(MqConstants.HOTEL_EXCHANGE, MqConstants.HOTEL_INSERT_KEY, hotel.getId().toString());
                logger.info("----- rabbitmq send message -----");

            }
        });

        logger.info("--------- out service ----------");
        //模拟异常
        int n =0/0;

        return false;
    }

注意： 上面的代码将在事务提交后执行.如果在非事务context中将抛出java.lang.IllegalStateException: Transaction synchronization is not active。

所以必须在service方法上添加 @Transactional注解。

2. 使用 TransactionSynchronizationAdapter 控制事务

配置类

import com.sun.istack.internal.NotNull;
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 javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.*;

@Component("afterCommitExecutor")
public class AfterCommitExecutor extends TransactionSynchronizationAdapter implements Executor {
    private static final ThreadLocal<List<Runnable>> RUNNABLES = new ThreadLocal<List<Runnable>>();
    private ThreadPoolExecutor threadPool;

    private Logger logger = LoggerFactory.getLogger(AfterCommitExecutor.class);
    
    @PostConstruct
    public void init() {
        logger.debug("初始化线程池。。。");
        int availableProcessors = Runtime.getRuntime().availableProcessors();
        if (0 >= availableProcessors) {
            availableProcessors = 1;
        }
        int maxPoolSize = (availableProcessors > 5) ? availableProcessors * 2 : 5;
        logger.debug("CPU Processors :%s MaxPoolSize:%s", availableProcessors, maxPoolSize);
        threadPool = new ThreadPoolExecutor(
            availableProcessors,
            maxPoolSize,
            60,
            TimeUnit.SECONDS,
            new LinkedBlockingQueue<Runnable>(maxPoolSize * 2),
            Executors.defaultThreadFactory(),
            new RejectedExecutionHandler() {
                @Override
                public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
                    logger.debug("Task:%s rejected", r.toString());
                    if (!executor.isShutdown()) {
                        executor.getQueue().poll();
                        executor.execute(r);
                    }
                }
            }
        );
    }

    @PreDestroy
    public void destroy() {
        logger.debug("销毁线程池。。。");
        if (null != threadPool && !threadPool.isShutdown()) {
            threadPool.shutdown();
        }
    }

    @Override
    public void execute(@NotNull Runnable runnable) {
        if (!TransactionSynchronizationManager.isSynchronizationActive()) {
            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() {
        logger.debug("事务提交完成处理 ... ");
        List<Runnable> threadRunnables = RUNNABLES.get();
        for (int i = 0; i < threadRunnables.size(); i++) {
            Runnable runnable = threadRunnables.get(i);
            try {
                threadPool.execute(runnable);
            } catch (RuntimeException e) {
                logger.error("", e);
            }
        }
    }

    @Override
    public void afterCompletion(int status) {
        logger.debug("事务处理完毕 .... ");
        RUNNABLES.remove();
    }
}

service代码

 @Transactional
    public boolean updateById(Hotel hotel) {
        logger.info("----- into service -----");

        //修改DB的数据
        hotelMapper.updateById(hotel);

        // 使用AfterCommitExecutor
        afterCommitExecutor.execute(new Runnable() {
            @Override
            public void run() {
                rabbitTemplate.convertAndSend(MqConstants.HOTEL_EXCHANGE, MqConstants.HOTEL_INSERT_KEY, hotel.getId().toString());
                logger.info("----- rabbitmq send message -----");
            }
        });

        logger.info("--------- out service ----------");
        int n =0/0;

        return false;
    }