Transacted Message in JMS
In a Java SE environment or in the Java EE
application client container:
If transacted is set to true then the session will
use a local transaction which may subsequently be committed or rolled back by
calling the session's commit or rollback methods. The argument
acknowledgeMode is ignored.
·
If transacted is set to false then the session will
be non-transacted. In this case the argument acknowledgeMode is used to specify
how messages received by this session will be acknowledged. The permitted
values are Session.CLIENT_ACKNOWLEDGE, Session.AUTO_ACKNOWLEDGE and Session.DUPS_OK_ACKNOWLEDGE. For a definition of
the meaning of these acknowledgement modes see the links below.
Modifier and Type
|
Field and Description
|
static
int
|
With this acknowledgment mode, the session
automatically acknowledges a client's receipt of a message either when the
session has successfully returned from a call to receive or when the message listener the session has
called to process the message successfully returns.
|
static
int
|
With this acknowledgment mode, the client
acknowledges a consumed message by calling the message's acknowledge method.
|
static
int
|
This acknowledgment mode instructs the session
to lazily acknowledge the delivery of messages.
|
static
int
|
This value may be passed as the argument to the
method createSession(int sessionMode) on the Connection object to specify that the session should use a
local transaction.
|
In a Java EE web or EJB container, when
there is an active JTA transaction in progress:
Both arguments transacted and acknowledgeMode are ignored. The
session will participate in the JTA transaction and will be committed or rolled
back when that transaction is committed or rolled back, not by calling the
session's commit or rollback methods. Since both
arguments are ignored, developers are recommended to use createSession(), which has no
arguments, instead of this method.
Interface TopicConnectionFactory
Modifier and Type
|
Method and
Description
|
|
Creates a
topic connection with the default user identity.
|
|
|
Creates a
topic connection with the specified user identity.
|
public class FirstClient {
private Context context = null;
private TopicConnectionFactory factory = null;
private TopicConnection
connection = null;
private TopicSession session = null;
private Topic topic = null;
private TopicPublisher publisher = null;
public FirstClient() {
Properties
initialProperties = new Properties();
initialProperties.put(InitialContext.INITIAL_CONTEXT_FACTORY,
"org.exolab.jms.jndi.InitialContextFactory");
initialProperties.put(InitialContext.PROVIDER_URL, "tcp://localhost:3035");
try {
context = new
InitialContext(initialProperties);
factory = (TopicConnectionFactory) context.lookup("ConnectionFactory");
topic = (Topic) context.lookup("topic1");
connection = factory.createTopicConnection();
session = connection.createTopicSession(false, //Transacted
TopicSession.AUTO_ACKNOWLEDGE);
publisher = session.createPublisher(topic);
EventMessage
eventMessage = new EventMessage(1, "Message
from FirstClient");
ObjectMessage
objectMessage = session.createObjectMessage();
objectMessage.setObject(eventMessage);
connection.start();
publisher.publish(objectMessage);
System.out.println(this.getClass().getName()+
"
has sent a message : " + eventMessage);
session.close();
connection.close();
context.close();
}
catch (Exception e) {
}
}
}
Synchronous Messaging and Asynchronous Messaging
In case of asynchronous consumption, the
consumer is implementing the MessageListener interface .So the overridden
onMessage() method gets the message. But in case of synchronous consumption,
the client is waiting to get the message since we used the receive() method of
the consumer.
public interface MessageListener
A MessageListener object
is used to receive asynchronously delivered messages.
Each session must ensure that it passes
messages serially to the listener. This means that a listener assigned to one
or more consumers of the same session can assume that the onMessage method
is not called with the next message until the session has completed the last
call.
Implement MessageListener Interface for implement
Asynchronous Consumer.
Modifier and Type
|
Method and
Description
|
void
|
Passes a
message to the listener.
|
JMS Reliablity Mechanisms-Message
persistence in JMS
1)Persistent delivery mode – This is the default delivery mode. It
forces the JMS provider to take extra care to avoid the loss of message in case
of failure. Message is persisted in secondary storage. When the provider comes
alive again message will be delivered to consumer. This ensures reliable
message delivery.
2)Non-Persistent
delivery mode– If we specify the delivery mode as non-persistent then the
provider is not taking extra effort to persist the message if a provider
failure occurs.
By using the setDeliveryMode(int
value) method of MessageProducer interface .
DeliveryMode.PERSISTENT
=2
DeliveryMode.NON_PERSISTENT=1
.
producer.setDeliveryMode(DeliveryMode.PERSISTENT);
Or Use the
overloaded send() or publish() method of MessageProducer interface .The second
argument in the method call specifies the delivery mode.
producer.send(message, DeliveryMode.PERSISTENT);
Setting Message Priority Levels in JMS
1.
Priority
levels – 0 to 9
2.
Default
Priority Level – 4
3.
Messages
having highest priority are delivered first.
4.
Setting
Message Priority
-By using
setPriority(int value) method of MessageProducer interface.
-By using
the overloaded publish() method.The third argument will be the priority.
void send(Message message,
int deliveryMode, int priority, long timeToLive) throws JMSException
topicPublisher.publish(message,
DeliveryMode.NON_PERSISTENT, 3,20000)
message - the
message to send
deliveryMode - the delivery mode to use
priority - the
priority for this message
timeToLive - the message's lifetime (in milliseconds)
Message Expiry in JMS
By default a message never expires.In some cases message will become obsolete after a particular time period. In such situation it is desirable to set expiration time . After the message expires, it will not be delivered.
We can set the expiration time in program in two ways.
Using setTimeToLive() method of MessageProducer interface to set the expiry time of messages from that producer.
Example: topPublisher .setTimeToLive(10000)
The above statement sets the expiry time 10000 milliseconds(10 seconds)
Using the overridden method publish() of MessageProducer
Example :topPublisher.publish(message, DeliveryMode.PERSISTENT, 3,10000)
The fourth argument gives the expiry time as 10000 milliseconds
The
reliability mechanisms we discussed so far are :
Creating Durable Subscriptions in JMS
This ensures message delivery to Subscriber, when it comes alive.
topic
= (Topic) context.lookup("topic1");
connection = factory.createTopicConnection();
session = connection.createTopicSession(false,TopicSession.AUTO_ACKNOWLEDGE);
subscriber = session.createDurableSubscriber(topic,"sampleSubscription");
// subscriber = session.createSubscriber(topic);
connection.start();
Message message = subscriber.receive();
connection = factory.createTopicConnection();
session = connection.createTopicSession(false,TopicSession.AUTO_ACKNOWLEDGE);
subscriber = session.createDurableSubscriber(topic,"sampleSubscription");
// subscriber = session.createSubscriber(topic);
connection.start();
Message message = subscriber.receive();
A durable subscriber can have only one active subscriber at a
time.
A durable subscriber
registers a durable subscription with a unique identity (“sampleSubscription” in above example). Subsequent
subscribers with the same identity will resume the subscription in the state
where the previous subscriber was left.
If there is no active subscriber, then the JMS provider keeps
the messages till they are received by any subscriber or till the message
expires.
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