RocketMQ如何解决分布式事务

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1.基本实现思路

a.生产者向我们的Broker（MQ服务器端）发送我们派单消息设置为半消息，该消息不可以被消费者消费。
b.在执行我们的本地的事务，将本地执行事务结果提交或者回滚告诉Broker
c.Broker获取本地事务的结果如果是已提交的话，将该半消息设置为允许被消费者消费，如果本地事务执行失败的情况下，将该半消息直接从Broker中移除
d.如果我们的本地事务没有将结果及时通知给我们的Broker，这时候我们Broker会主动定时（默认60s）查询本地事务结果
e.本地事务结果实际上就是一个回调方法，根据自己业务场景封装本地事务结果
事务回查的时间次数等配置在broker里

2.代码示例

2.1 生产者消息发送

/**
 * 生产者消息发送
 */
@Service
public class OrderService {

    @Autowired
    private RocketMQTemplate rocketMQTemplate;

    public String sendOrder() {
        //数据封装
        String orderId = (new Random().nextInt(1000)) +"";
        UserEntity entity = new UserEntity();
        entity.setId(Long.valueOf(orderId));
        entity.setAge(12);
        entity.setName("张三");
        String mm = JSON.toJSONString(entity);
        //消息封装
        MessageBuilder stringMessageBuilder = MessageBuilder.withPayload(mm);
        stringMessageBuilder.setHeader("msg",mm);
        Message msg = stringMessageBuilder.build();
        //发送半消息
        rocketMQTemplate.sendMessageInTransaction("tt0103","tpc0103",msg,null);
        return orderId;
    }
}

2.2 生产者监听程序

/**
 * 生产者监听程序
 */
@Slf4j
@Component
@RocketMQTransactionListener(txProducerGroup = "tt0103")
public class SyncProducerListener implements RocketMQLocalTransactionListener {

    @Autowired
    private TransationalUtils transationalUtils;
    @Autowired
    private OrderMapper orderMapper;


    /**
     * 执行本地事务
     */
    @Override
    public RocketMQLocalTransactionState executeLocalTransaction(Message message, Object o) {
        TransactionStatus beginStatus = null;
        try {
            beginStatus = transationalUtils.begin();
            MessageHeaders headers = message.getHeaders();
            String objMsg = (String) headers.get("msg");
            if (StringUtils.isEmpty(objMsg)) {
                return RocketMQLocalTransactionState.ROLLBACK;
            }
            UserEntity orderEntity = JSONObject.parseObject(objMsg, UserEntity.class);
            int result = orderMapper.addOrder(orderEntity);
            if (result > 0) {
                transationalUtils.commit(beginStatus);
            }
            log.info("【本地业务执行完毕】 msg:{}, Object:{}", message, o);
            return RocketMQLocalTransactionState.COMMIT;
        } catch (Exception e) {
            e.printStackTrace();
            log.error("【执行本地业务异常】 exception message:{}", e.getMessage());
            if (beginStatus != null) {
                transationalUtils.rollback(beginStatus);
            }
            return RocketMQLocalTransactionState.ROLLBACK;
        }
    }

    /**
     * rocketmq主动查询本地事务提交情况
     * @param message
     * @return
     */
    @Override
    public RocketMQLocalTransactionState checkLocalTransaction(Message message) {
        log.info("【执行检查任务】");
        MessageHeaders headers = message.getHeaders();
        String objMsg = (String) headers.get("msg");
        if (StringUtils.isEmpty(objMsg)) {
            return RocketMQLocalTransactionState.UNKNOWN;
        }
        UserEntity orderEntity = JSONObject.parseObject(objMsg, UserEntity.class);
        Long orderId = orderEntity.getId();
        UserEntity orderDbEntity = orderMapper.findOrderId(orderId);
        if (orderDbEntity == null) {
            return RocketMQLocalTransactionState.UNKNOWN;
        }
        return RocketMQLocalTransactionState.COMMIT;
    }
}

2.3消费者消费

/**
 * 消费者消费
 */
@Service
@RocketMQMessageListener(topic = "tpc0103", consumerGroup = "cpc0103")
public class OrdeConsumer implements RocketMQListener {

    @Override
    public void onMessage(String msg) {
        UserEntity orderEntity = JSONObject.parseObject(msg, UserEntity.class);
        System.out.println(orderEntity.toString());
    }

}

2.4异常情况

报错：The producer group has been created before, specify another name please.

producer.setInstanceName(producer.buildMQClientId());

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