线程池activemq侦听器

Question

我使用2个线程来侦听ActiveMQ消息，使用列表来缓存消息，直到大小达到5，侦听器将对其进行处理。但是消息重复，为什么？ 我只发送10条消息，但消息未到达10次。

@Component
public class Consumer {

    private static final Logger log = LoggerFactory.getLogger(Consumer.class);

    private List<TextMessage> list =  Collections.synchronizedList(new ArrayList<TextMessage>());


    @JmsListener(destination = "HelloWorldQueue")
    public void receiveQueue(TextMessage msg)  throws Exception {
        log.info("message arrive: {}", msg.getText());
        batchProcess(msg);
    }

    private void batchProcess(TextMessage msg) {
        list.add(msg);
        if (list.size() >= 5) {
            log.info("start batch:");
            Iterator<TextMessage> it = list.iterator();
            while(it.hasNext()) {
                process(it.next());
                it.remove();
            }
        }
    }

    private void process(TextMessage msg) {

      log.info("process: {}", msg.getText());

    }
}