java - JMS 队列接收消息？

Question

在 JMS API 文档中，它说:

public Message receive() throws JMSException

Receives the next message produced for this message consumer. This call blocks indefinitely until a message is produced or until this message consumer is closed.

If this receive is done within a transaction, the consumer retains the message until the transaction commits.

这里我有三个问题:1. 在代码中，我们是否需要while循环来接收消息？喜欢:

while(true){
    Message msg = queue.receive();
    ....
}

1. 交易设置是什么？如何提交交易？像这样:

   boolean transacted = false;
   session = connection.createQueueSession(transacted, Session.AUTO_ACKNOWLEDGE);
   

2. receiveNoWait() 有事务支持吗？如何使用它？

谢谢

Answer 1

1. 如果您打算使用 receive，那么您将需要某种循环以在收到第一个消息后继续接收消息。请记住，您还可以设置消息监听器并通过回调方法异步接收消息，而不必阻塞。

2. 默认情况下，事务通常设置为 AUTO_ACKNOWLEDGE，这意味着一旦消息从队列中取出，它就会消失并且无法回滚。如果要设置事务，则需要将 session 设置为事务处理并将方法设置为 SESSION_TRANSACTED。当您在 session 中调用 commit() 时，消息将在队列中得到确认。

3. 如果您正确设置确认模式并在 session 中使用 commit() 和 rollback()，则 receiveNoWait() 可以具有事务支持。

如果我是你，我会创建一个 MessageListener 而不必担心旋转一个线程来轮询接收方法。请记住，一旦 session 创建，隐式事务就会启动。

public class JmsAdapter implements MessageListener, ExceptionListener
{
    private ConnectionFactory connFactory = null;
    private Connection conn = null;
    private Session session = null;

    public void receiveMessages() 
    {
        try
        {
            this.session = this.conn.createSession(true, Session.SESSION_TRANSACTED);

            this.conn.setExceptionListener(this);

            Destination destination = this.session.createQueue("SOME_QUEUE_NAME");

            this.consumer = this.session.createConsumer(destination);

            this.consumer.setMessageListener(this);

            this.conn.start();
        } 
        catch (JMSException e) 
        {
            //Handle JMS Exceptions Here
        }
    }

    @Override
    public void onMessage(Message message) 
    {
        try
        {
            //Do Message Processing Here

            //Message sucessfully processed...  Go ahead and commit the transaction.
            this.session.commit();
        }
        catch(SomeApplicationException e)
        {
            //Message processing failed.
            //Do whatever you need to do here for the exception.

            //NOTE: You may need to check the redelivery count of this message first
            //and just commit it after it fails a predefined number of times (Make sure you
            //store it somewhere if you don't want to lose it).  This way you're process isn't
            //handling the same failed message over and over again.
            this.session.rollback()
        }
    }
}