Re: Message-Driven Bean OnMesssage() etc

I see.
How do you know there isn't another yet not arrived message with a
higher priority? E.g. what is the trigger to start forwarding
messages? The priority field is probably your only option, if your
scenarioo is to always forward the highest-priority message available
on the queue at any given time. If the sender is out of your control
(which I guess implies that you determine the priority from the
payload), your safest, most scalable and most portable option (not
bad, ehe?) i probably to design two MDBs - one that consumes messages
from the destination, determines the priority and sends the message
as is to a new destination, but this time with the priority assigned
to the JMSPriority header field, which would allow a second MDB to
consume them in the order you needs to have them processed. But I
still have a hard time understanding you business case. Is the
original sender batching out messages and you need to process them in
priority within the batch? Some more background info would help.

/Johan

3 jan 2006 kl. 17.13 skrev Zerbe John W:

> Are you using the JMSPriority field?
> If so, you should be able to configure your message engine to
> deliver the
> messages in priority order rather than FIFO.
> Using an "in memory" structure for this sort of thing (reordering
> of messages)
> is generally not a good idea.
>
> If you ever need to scale up with multiple instances of the JVM on
> potentially separate machines, you won't have access to the same
> data structures from the separate instances.
>
>
>
> -----Original Message-----
> From: A mailing list for Enterprise JavaBeans development
> [mailto:[email protected]]On Behalf Of Jingwen Jin
> Sent: Sunday, January 01, 2006 12:42 PM
> To: [email protected]
> Subject: Re: Message-Driven Bean OnMesssage() etc
>
>
> Hi Johan,
>
> Thank you again for the generous response. I sent the following
> text to Mark
> Birenbaum on this list who responded me earlier. I'm posting the
> message to the
> group in the hope of getting feedbacks faster.
>
> ------------------------------------------------------------------
> The reason I wanted to store incoming messages first is that I
> wanted the
> messages to get ordered based on their priority (determined by
> their urgency and
> importance), and have another thread or MDB deliver the messages in
> order. So I
> do need the two entities to share a common in-memory data
> structure. Doing this
> with regular threading is natural. But how can I simulate this
> (sharing of a
> common object) with multiple MDBs?
>
> -------------------------------------------------------------------
>
> Thanks, and Happy New Year,
>
> Jingwen
>
> ---- Original message ----
>> Date: Sun, 1 Jan 2006 16:18:06 +0100
>> From: Johan Eltes <[email protected]>
>> Subject: Re: Message-Driven Bean OnMesssage() etc
>> To: Jingwen Jin <[email protected]>
>> Cc: [email protected]
>>
>> If you have many MDB instances (e.g. threaded MDBs) simultaneously
>> pulling messages off the queue/topic, you could let each mdb instance
>> forward the message without creating a new thread. You wouldn't
>> usually need to do asynchronous *wihin* an MDB, since the MDB is
>> asynchronous itself. What exactly is it you need to achieve by
>> threading, in addition to what you get by having an MDB?
>>
>> /Johan
>>
>> 1 jan 2006 kl. 01.06 skrev Jingwen Jin:
>>
>>> Hi, Thanks a lot for the suggestion. The fact that EJB does not
>>> support
>>> multi-threading surprised me. As I said, I wanted my MDB to store
>>> incoming
>>> messages in a data structure, and then have threads working on the
>>> sending of
>>> messages. How could such a task be achieved by using multiple
>>> beans? More
>>> details would be very helpful.
>>>
>>> When google-ing, I found somebody commenting that multi-threading
>>> would work
>>> when separating the "multi threadedness" into a separate layer
>>> outside of the
>>> EJB layer. In such a case, a java job scheduler is needed to handle
>>> the
>>> scheduling. Have you or has anybody on the list used any scheduler
>>> (such as the
>>> Quartz scheduler)?
>>>
>>> Thank you,
>>>
>>> Jingwen
>>>
>>>
>>> ---- Original message ----
>>>> Date: Thu, 29 Dec 2005 09:29:03 +0100
>>>> From: Johan Eltes <[email protected]>
>>>> Subject: Re: Message-Driven Bean OnMesssage() etc
>>>> To: [email protected]
>>>>
>>>> You are not allowed to create threads in an EJB.
>>>> One of the reasons is that transaction contexts are bound to
>>>> threads.
>>>> If you create a thread (most app servers will not let you), that
>>>> the
>>>> app server will not be able to manage it.
>>>>
>>>> Would it be possible to have multiple MDBs (MDB pool size > 1)
>>>> instead of forking threads within your business logic?
>>>>
>>>> /Johan
>>>>
>>>> 29 dec 2005 kl. 06.00 skrev Jingwen Jin:
>>>>
>>>>> I'm writing a pub/sub server that, on receiving an incoming
>>>>> message,
>>>>> stores it into a messageArray, and then creates a thread to
>>>>> forward
>>>>> messages in the array. The following code works ok if the
>>>>> "forwardMessage"
>>>>> method is called within onMessage(); messages get delivered.
>>>>>
>>>>> But whenever I try to deliver the messages in messageArray using a
>>>>> thread
>>>>> as shown below, I get the following exception and messages
>>>>> don't get
>>>>> delivered:
>>>>>
>>>>> ReplyMsgBean.forwardMessage: JMSException:
>>>>> com.sun.messaging.jms.JMSException: [SEND_REPLY(9)] [C4036]: A
>>>>> server
>>>>> error occurred. : transaction failed: Unexpected Broker Exception:
>>>>> [received message with Unknown Transaction ID -1: ignoring
>>>>> message]
>>>>>
>>>>> It looks like the server could not create the connection within
>>>>> the
>>>>> forwardMessage method.
>>>>>
>>>>> I'd appreciate any suggestions.
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Jingwen
>>>>>
>>>>> ---------------------------------
>>>>>
>>>>>
>>>>>
>>>>> public class ReplyMsgBean implements MessageDrivenBean,
>>>>> MessageListener {
>>>>> ...
>>>>>     public ReplyMsgBean() throws Exception {
>>>>>  messageArray = new ArrayList();
>>>>>  mft = new MessageForwardingThread();
>>>>>  mft.start();
>>>>>     }
>>>>>     public void ejbCreate() {
>>>>>         try {
>>>>>             Context initial = new InitialContext();
>>>>>             cf = (ConnectionFactory) initial.lookup(
>>>>>                     "java:comp/env/jms/MyConnectionFactory");
>>>>>         } catch (Exception ex) {
>>>>>             logger.severe("ReplyMsgBean.ejbCreate: Exception: " +
>>>>>                 ex.toString());
>>>>>         }
>>>>>     }
>>>>>     public void onMessage(Message inMessage) {
>>>>>        put the message into messageArray
>>>>>     }
>>>>>     private static void forwardMessage(TextMessage msg) {
>>>>>          ...
>>>>>          Connection con = cf.createConnection();
>>>>>          Session ses = con.createSession(true, 0);
>>>>>          producer = ses.createProducer(topic);
>>>>>  producer.send(msg);
>>>>>          con.close();
>>>>>     }
>>>>>
>>>>>
>>>>>    final class MessageForwardingThread extends Thread {
>>>>>          ...
>>>>>  public final void run() {
>>>>>              for every-message (msg) in messageArray
>>>>>   ReplyMsgBean.forwardMessage(msg);
>>>>>
>>>>>  }
>>>>>
>>>>>    }
>>>>>
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