Background

Ali's RicketMQ has been castrated in previous versions and re-added in the new version to solve the problem that small companies are unable to make reliable messaging middleware products. At the same time, RocketMQ also refers to the Kafka implementation, and its performance is very good.

Version 2

<dependency>
    <groupId>org.apache.rocketmq</groupId>
    <artifactId>rocketmq-spring-boot-starter</artifactId>
    <version>2.0.3</version>
</dependency>

3. Source Code Interpretation

Official demo

@SpringBootApplication
public class ProducerApplication implements CommandLineRunner {
    private static final String TX_PGROUP_NAME = "myTxProducerGroup";
    @Resource
    private RocketMQTemplate rocketMQTemplate;
    @Value("${demo.rocketmq.transTopic}")
    private String springTransTopic;


    public static void main(String[] args) {
        SpringApplication.run(ProducerApplication.class, args);
    }

    @Override
    public void run(String... args) throws Exception {
        // Send transactional messages
        testTransaction();
    }
    
    private void testTransaction() throws MessagingException {
        String[] tags = new String[]{"TagA", "TagB", "TagC", "TagD", "TagE"};
        for (int i = 0; i < 10; i++) {
            try {

                Message msg = MessageBuilder
                                        .withPayload("Hello RocketMQ " + i)
                                        .setHeader(RocketMQHeaders.TRANSACTION_ID, "KEY_" + i)
                                        .build();
                SendResult sendResult = rocketMQTemplate.sendMessageInTransaction(TX_PGROUP_NAME,
                                                                        springTransTopic + ":" + tags[i % tags.length],
                                                                        msg,
                                                                        null);
                System.out.printf("------ send Transactional msg body = %s , sendResult=%s %n",
                                    msg.getPayload(),
                                    sendResult.getSendStatus());

                Thread.sleep(10);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    @RocketMQTransactionListener(txProducerGroup = TX_PGROUP_NAME)
    class TransactionListenerImpl implements RocketMQLocalTransactionListener {
        private AtomicInteger transactionIndex = new AtomicInteger(0);

        private ConcurrentHashMap<String, Integer> localTrans = new ConcurrentHashMap<>();

        @Override
        public RocketMQLocalTransactionState executeLocalTransaction(Message msg, Object arg) {
            String transId = (String)msg.getHeaders().get(RocketMQHeaders.TRANSACTION_ID);
            System.out.printf("#### executeLocalTransaction is executed, msgTransactionId=%s %n", transId);
            int value = transactionIndex.getAndIncrement();
            int status = value % 3;
            localTrans.put(transId, status);
            if (status == 0) {
                // Return local transaction with success(commit), in this case,
                // this message will not be checked in checkLocalTransaction()
                System.out.printf("    # COMMIT # Simulating msg %s related local transaction exec succeeded! ### %n", msg.getPayload());
                return RocketMQLocalTransactionState.COMMIT;
            }

            if (status == 1) {
                // Return local transaction with failure(rollback) , in this case,
                // this message will not be checked in checkLocalTransaction()
                System.out.printf("    # ROLLBACK # Simulating %s related local transaction exec failed! %n", msg.getPayload());
                return RocketMQLocalTransactionState.ROLLBACK;
            }

            System.out.printf("    # UNKNOW # Simulating %s related local transaction exec UNKNOWN! \n");
            return RocketMQLocalTransactionState.UNKNOWN;
        }

        @Override
        public RocketMQLocalTransactionState checkLocalTransaction(Message msg) {
            String transId = (String)msg.getHeaders().get(RocketMQHeaders.TRANSACTION_ID);
            RocketMQLocalTransactionState retState = RocketMQLocalTransactionState.COMMIT;
            Integer status = localTrans.get(transId);
            if (null != status) {
                switch (status) {
                    case 0:
                        retState = RocketMQLocalTransactionState.UNKNOWN;
                        break;
                    case 1:
                        retState = RocketMQLocalTransactionState.COMMIT;
                        break;
                    case 2:
                        retState = RocketMQLocalTransactionState.ROLLBACK;
                        break;
                }
            }
            System.out.printf("------ !!! checkLocalTransaction is executed once," +
                    " msgTransactionId=%s, TransactionState=%s status=%s %n",
                transId, retState, status);
            return retState;
        }
    }

}

The transaction message calls RocketMQTemplate.sendMessageInTransaction(), so start here.

//RocketMQTemplate

public TransactionSendResult sendMessageInTransaction(final String txProducerGroup, final String destination, final Message<?> message, final Object arg) throws MessagingException {
    try {
        //Producer who retrieves the producer group name from the local cache
        TransactionMQProducer txProducer = this.stageMQProducer(txProducerGroup);
        org.apache.rocketmq.common.message.Message rocketMsg = RocketMQUtil.convertToRocketMessage(objectMapper,
                                                                                                   charset, destination, message);
        return txProducer.sendMessageInTransaction(rocketMsg, arg);
    } catch (MQClientException e) {
        throw RocketMQUtil.convert(e);
    }
}

Enter txProducer.sendMessageInTransaction(rocketMsg, arg)

//TransactionMQProducer

public TransactionSendResult sendMessageInTransaction(final Message msg,
        final Object arg) throws MQClientException {
    //Have you set up a transaction listener (local transaction, return inquiry)
    if (null == this.transactionListener) {
        throw new MQClientException("TransactionListener is null", null);
    }

    return this.defaultMQProducerImpl.sendMessageInTransaction(msg, null, arg);
}

Enter defaultMQ ProducerImpl. sendMessageInTransaction (msg, null, arg)

//DefaultMQProducerImpl

public TransactionSendResult sendMessageInTransaction(final Message msg,
                                                          final LocalTransactionExecuter localTransactionExecuter, final Object arg)
        throws MQClientException {
    TransactionListener transactionListener = getCheckListener();
    if (null == localTransactionExecuter && null == transactionListener) {
        throw new MQClientException("tranExecutor is null", null);
    }
    Validators.checkMessage(msg, this.defaultMQProducer);

    SendResult sendResult = null;
	//Set to Pre-message
    MessageAccessor.putProperty(msg, MessageConst.PROPERTY_TRANSACTION_PREPARED, "true");
    MessageAccessor.putProperty(msg, MessageConst.PROPERTY_PRODUCER_GROUP, this.defaultMQProducer.getProducerGroup());
    try {
        //send message
        sendResult = this.send(msg);
    } catch (Exception e) {
        throw new MQClientException("send message Exception", e);
    }

    LocalTransactionState localTransactionState = LocalTransactionState.UNKNOW;
    Throwable localException = null;
    switch (sendResult.getSendStatus()) {
        //Send successfully, when isWaitStoreMsgOK=true (default true) in the message object, if isWaitStoreMsgOK=false, when no exception is caught, then return SEND_OK
        case SEND_OK: {
            try {
                if (sendResult.getTransactionId() != null) {
                    msg.putUserProperty("__transactionId__", sendResult.getTransactionId());
                }
                String transactionId = msg.getProperty(MessageConst.PROPERTY_UNIQ_CLIENT_MESSAGE_ID_KEYIDX);
                if (null != transactionId && !"".equals(transactionId)) {
                    msg.setTransactionId(transactionId);
                }
                //Execute incoming local branch transactions
                if (null != localTransactionExecuter) {
                    localTransactionState = localTransactionExecuter.executeLocalTransactionBranch(msg, arg);
                //Execute annotations or construct incoming transaction listeners by the producer
                } else if (transactionListener != null) {
                    log.debug("Used new transaction API");
                    localTransactionState = transactionListener.executeLocalTransaction(msg, arg);
                }
                if (null == localTransactionState) {
                    localTransactionState = LocalTransactionState.UNKNOW;
                }

                if (localTransactionState != LocalTransactionState.COMMIT_MESSAGE) {
                    log.info("executeLocalTransactionBranch return {}", localTransactionState);
                    log.info(msg.toString());
                }
            } catch (Throwable e) {
                log.info("executeLocalTransactionBranch exception", e);
                log.info(msg.toString());
                localException = e;
            }
        }
            break;
        //Brush disk timeout
        case FLUSH_DISK_TIMEOUT:
        //Timeout of data synchronization to Slave server
        case FLUSH_SLAVE_TIMEOUT:
        //No Slave server available
        case SLAVE_NOT_AVAILABLE:
            localTransactionState = LocalTransactionState.ROLLBACK_MESSAGE;
            break;
        default:
            break;
    }

    try {
        //Send a second confirmation message
        this.endTransaction(sendResult, localTransactionState, localException);
    } catch (Exception e) {
        log.warn("local transaction execute " + localTransactionState + ", but end broker transaction failed", e);
    }
    //Encapsulating execution results
    TransactionSendResult transactionSendResult = new TransactionSendResult();
    transactionSendResult.setSendStatus(sendResult.getSendStatus());
    transactionSendResult.setMessageQueue(sendResult.getMessageQueue());
    transactionSendResult.setMsgId(sendResult.getMsgId());
    transactionSendResult.setQueueOffset(sendResult.getQueueOffset());
    transactionSendResult.setTransactionId(sendResult.getTransactionId());
    transactionSendResult.setLocalTransactionState(localTransactionState);
    return transactionSendResult;
}


public void endTransaction(
        final SendResult sendResult,
        final LocalTransactionState localTransactionState,
        final Throwable localException) throws RemotingException, MQBrokerException, InterruptedException, UnknownHostException {
    
    final MessageId id;
    if (sendResult.getOffsetMsgId() != null) {
        id = MessageDecoder.decodeMessageId(sendResult.getOffsetMsgId());
    } else {
        id = MessageDecoder.decodeMessageId(sendResult.getMsgId());
    }
    String transactionId = sendResult.getTransactionId();
    final String brokerAddr = this.mQClientFactory.findBrokerAddressInPublish(sendResult.getMessageQueue().getBrokerName());
    EndTransactionRequestHeader requestHeader = new EndTransactionRequestHeader();
    requestHeader.setTransactionId(transactionId);
    requestHeader.setCommitLogOffset(id.getOffset());
    switch (localTransactionState) {
        //Submission of affairs
        case COMMIT_MESSAGE:
            requestHeader.setCommitOrRollback(MessageSysFlag.TRANSACTION_COMMIT_TYPE);
            break;
        //Submission of affairs
        case ROLLBACK_MESSAGE:
            requestHeader.setCommitOrRollback(MessageSysFlag.TRANSACTION_ROLLBACK_TYPE);
            break;
        //Submission of affairs
        case UNKNOW:
            requestHeader.setCommitOrRollback(MessageSysFlag.TRANSACTION_NOT_TYPE);
            break;
        default:
            break;
    }

    requestHeader.setProducerGroup(this.defaultMQProducer.getProducerGroup());
    requestHeader.setTranStateTableOffset(sendResult.getQueueOffset());
    requestHeader.setMsgId(sendResult.getMsgId());
    String remark = localException != null ? ("executeLocalTransactionBranch exception: " + localException.toString()) : null;
    
    //One-way send a second confirmation message without the corresponding server, which is compensated by message back-check and listening.
    this.mQClientFactory.getMQClientAPIImpl().endTransactionOneway(brokerAddr, requestHeader, remark,
                                                                   this.defaultMQProducer.getSendMsgTimeout());
}