Duplicate Messages sent

Question

Hi there,
I am trying to figure out why I receive duplicate messages from my message queue. We have our Entity Beans send out messages when their state changes. When the beans are deployed first, and their state changes, only a single message is sent out, but if the state of the bean is changed again, then multiple messages are sent out. I guess the message queue does not get flushed after the delivery of the messages. Can any one shed some light on this issue?
Here is my client code, which is gui.
try {
TopicConnectionFactory factory = serviceLocator.getTopicConnectionFactory("jms/TopicConnectionFactory");
Topic topic = serviceLocator.getTopic("jms/jtTopic");
TopicConnection connect = factory.createTopicConnection();
TopicSession session = connect.createTopicSession(false, Session.CLIENT_ACKNOWLEDGE);
TopicSubscriber subscriber = session.createSubscriber(topic);
subscriber.setMessageListener(this);
System.out.println("Listening for messages on topic/rhythm-employee...");
// calls onMessage();
connect.start();
} catch (NamingException ne) {
ne.printStackTrace();
} catch (JMSException jme) {
jme.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
And here is the onMessage code:
public synchronized void onMessage(Message message) {
try {
ObjectMessage oMsg = (ObjectMessage) message;
String jobName = oMsg.getStringProperty("jobName");
String scnName = oMsg.getStringProperty("scnName");
if (oMsg.getStringProperty("actionType").equals("scene")) {
SceneTO sceneTO = (SceneTO) oMsg.getObject();
System.out.println("Scene Name: " + sceneTO.getSceneName());
final Object obj = oMsg.getObject();
Hashtable hash;
if (obj instanceof SceneTO) {
JTBase.jobLock.lock();
hash = (Hashtable) JTBase.Jobs.get(jobName);
if (!hash.containsKey(scnName)) {
hash.put(scnName,new Hashtable());
hash = (Hashtable) hash.get(scnName);
if (!hash.containsKey("Scene Info")) {
hash.put("Scene Info",new Hashtable());
hash = (Hashtable) hash.get("Scene Info");
if (hash.containsKey("data")) {
hash.remove("data");
hash.put("data",obj);
JTBase.jobLock.releaseLock();
// Refresh if needed
if(JTBase.jobName.equals(jobName) && JTBase.scnName.equals(scnName)) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
updateHeader(obj);
if (JTBase.tabName.equals("Scene Info")) {
updateMain("Refresh");
oMsg.clearBody();
message.acknowledge();
} catch(JMSException jmsE) {
JTBase.jobLock.releaseLock();
jmsE.printStackTrace();
Thanks in advance
-r

Answer 1

Hi,
<rhajikhani1>
When the beans are deployed first, and their state changes, only a single message is sent out, but if the state of the bean is changed again, then multiple messages are sent out
</rhajikhani1>
Does this not sound like a problem at the sending-side (your Entity Bean) rather than the receiving-side (the GUI code you have below).
You say that when the Entity Bean is deployed it sends one message which (I assume) is handled OK by the GUI code. Then, when the Entitiy Bean changes it starts sending multiple messages, isn't this a problem with the Entity Bean message sending code?
Anyway, if you are sure it is the receiver side I suggest placing a try catch (Throwable) around the code in the onMessage and printing the stack trace. At the moment you only catch JMSExceptions. The reason I say this is that maybe the message.acknowledge line is not being called which has resulted in a redelivery for some reason.
I can see several points in your code where a NullPointerException could be raised which would result in the message not being acknowledged. For example if the message does not contain the property "scnName" then a NullPointerException will be thrown by the call to hash.containsKey(scnName). If you were to catch Throwables then you can tell if there is a problem with the onMessage method (or the messages it is receiving).
Hope this helps,
Tom Jenkinson
Arjuna Technologies Limited