java - 从队列中接收消息数

Question

我正在接收来自 Active MQ 队列的消息。

有没有办法一次接收多条消息？还是必须通过循环来完成？

此外，如果我想说 30 条消息运行一个过程，并且只有当该过程有效时，才会 message.acknowledge();为所有消息返回一个。

我的意思是如果程序失败，我不想从队列中删除这 30 个。

谢谢。

Answer 1

您必须循环执行。通常，最好使用消息驱动的 bean 来消费消息，但它不适合这种情况，因为它们逐条接收消息并且您无法指定确切的数量。因此，使用MessageConsumer和手动交易：

@Resource
UserTransaction utx;

@Resource(mappedName="jms/yourConnectionFactory");
ConnectionFactory cf;

@Resource(mappedName="jms/yourQueue");
Queue queue;

..    
Connection conn = null;
Session s = null;
MessageConsumer mc = null;
try {
    utx.begin();
    conn = cf.createConnection();
    s = conn.createSession(true, Session.CLIENT_ACKNOWLEDGE); //TRANSACTIONAL SESSION!
    mc = s.createConsumer(queue);
    conn.start(); // START CONNECTION'S DELIVERY OF INCOMING MESSAGES
    for(int i=0; i<30; i++)
    {
          Message msg = mc.receive();
          //BUSINESS LOGIC
    }
    utx.commit();
} catch(Exception ex) {
  ..
} finally { //CLOSE CONNECTION, SESSION AND MESSAGE CONSUMER
}

Answer 2

I don't have any experience in ActiveMQ. But I think in case of queue listeners, basic logic should be the same independent to the queue implementation.

For your first question I don't know any way of retrieving multiple messages from a queue. I think best way would be to fetch it one by one inside a loop.

For your second question, message will not be discarded from the queue till the underlying transaction which read the message commits. So you could read whole bunch of messages in a single transaction and roll it back in case of an error. It shouldn't erase any existing messages from the queue.

May I ask why do you need 30 messages to run a procedure. Usually when we use a queue, each message should be able to process independently.