摘要

1. 事务消息是在发送端提供一种消息回查机制，如果消息发送状态是LocalTransactionState.COMMIT_MESSAGE，则表明本地消息发送成功，如果消息发送状态是 ROLLBACK_MESSAGE，则消息发送失败，消费端不会消费这条消息；如果消息发送状态是UNKNOW，则会一直调用 listener 里面的checkLocalTransaction回查本地状态。事务消息只对消息发送端提供一种回查机制，消息消费端没有什么特殊的。Push模式的消费端，提供至少消费一次的保证。
2. 事务消息失败会回查，最多15次，时间间隔一分钟。见

org.apache.rocketmq.common.BrokerConfig.transactionCheckMax = 15;org.apache.rocketmq.common.BrokerConfig.transactionCheckInterval = 60 * 1000;

示例

Producer消息发送

public class TransactionListenerImpl implements TransactionListener {    private AtomicInteger transactionIndex = new AtomicInteger(0);    private ConcurrentHashMap
    
      localTrans = new ConcurrentHashMap<>();    /**     * 在你的prepare消息到达broker的时候调用这个方法     * 此时消息并没有被被消费者消费     * 如果本方法执行成功(commit)或者失败(rollback)，则不会执行checkLocalTransaction方法     *          UNKNOW,才会调用checkLocalTransaction回查，回查频率间隔1分钟     */    @Override    public LocalTransactionState executeLocalTransaction(Message msg, Object arg) {        int value = transactionIndex.getAndIncrement();        int status = value % 3;        localTrans.put(msg.getTransactionId(), status);        System.out.println("执行 executeLocalTransaction 方法");        return LocalTransactionState.COMMIT_MESSAGE;    }    @Override    public LocalTransactionState checkLocalTransaction(MessageExt msg) {        Integer status = localTrans.get(msg.getTransactionId());//        if (null != status) {//            switch (status) {//                case 0://                    return LocalTransactionState.COMMIT_MESSAGE;//                case 1://                    return LocalTransactionState.COMMIT_MESSAGE;//                case 2://                    return LocalTransactionState.ROLLBACK_MESSAGE;//                default://                    return LocalTransactionState.COMMIT_MESSAGE;//            }//        }        System.out.println("执行 checkLocalTransaction 方法," + LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));        System.out.println();        return LocalTransactionState.COMMIT_MESSAGE;    }}
    

Producer的listener

public class TransactionListenerImpl implements TransactionListener {    private AtomicInteger transactionIndex = new AtomicInteger(0);    private ConcurrentHashMap
    
      localTrans = new ConcurrentHashMap<>();    /**     * 在你的prepare消息到达broker的时候调用这个方法     * 此时消息并没有被被消费者消费     * 如果本方法执行成功(commit)或者失败(rollback)，则不会执行checkLocalTransaction方法     *          UNKNOW,才会调用checkLocalTransaction回查，回查频率间隔1分钟     */    @Override    public LocalTransactionState executeLocalTransaction(Message msg, Object arg) {        int value = transactionIndex.getAndIncrement();        int status = value % 3;        localTrans.put(msg.getTransactionId(), status);        System.out.println("执行 executeLocalTransaction 方法");        return LocalTransactionState.COMMIT_MESSAGE;    }    @Override    public LocalTransactionState checkLocalTransaction(MessageExt msg) {        Integer status = localTrans.get(msg.getTransactionId());//        if (null != status) {//            switch (status) {//                case 0://                    return LocalTransactionState.COMMIT_MESSAGE;//                case 1://                    return LocalTransactionState.COMMIT_MESSAGE;//                case 2://                    return LocalTransactionState.ROLLBACK_MESSAGE;//                default://                    return LocalTransactionState.COMMIT_MESSAGE;//            }//        }        System.out.println("执行 checkLocalTransaction 方法," + LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));        System.out.println();        return LocalTransactionState.COMMIT_MESSAGE;    }}
    

consumer消息消费

public class PushConsumer {    public static void main(String[] args) throws InterruptedException, MQClientException {        DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("PUSH_CONSUME_GROUP");        consumer.setNamesrvAddr("localhost:9876");        consumer.subscribe("TOPIC_TEST", "*");// topic  tag        /**         * 全新的消费组 才适用这些策略         * CONSUME_FROM_LAST_OFFSET //默认策略，从该队列最尾开始消费，即跳过历史消息		 * CONSUME_FROM_FIRST_OFFSET //从队列最开始开始消费，即历史消息（还储存在broker的）全部消费一遍         * CONSUME_FROM_TIMESTAMP//从某个时间点开始消费，和setConsumeTimestamp()配合使用，默认是半个小时以前         *///        consumer.setConsumeFromWhere(ConsumeFromWhere.CONSUME_FROM_LAST_OFFSET);//        consumer.setConsumeTimestamp("20170422221800"); //时间格式 yyyyMMddHHmmss        consumer.registerMessageListener(new MessageListenerConcurrently() {            @Override            public ConsumeConcurrentlyStatus consumeMessage(List
    
      msgs, ConsumeConcurrentlyContext context) {                System.out.printf("%s Receive New Messages: %s %n", Thread.currentThread().getName(), msgs);                for(MessageExt msg:msgs){                	System.out.println("msgId:"+msg.getMsgId() + " body:" + new String(msg.getBody()));                }                /**                 * CONSUME_SUCCESS 消费成功                 * RECONSUME_LATER 重试消费，重试次数可以设置，默认是16次                 */                return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;//            }        });        consumer.start();        System.out.printf("Consumer Started.%n");    }}
    

源码阅读

参考文档