Explains Topics in JMS

1. Karthik
*

2. * JMS (Java Message Service) is a widely-used API for Message Oriented
Middleware. It allows communication between different components of
a distributed application to be loosely coupled, reliable, and
asynchronous.
* JMS supports two models for messaging:
• Queues - Point-to-point
• Topics - Publish and subscribe
* Mule's JMS transport lets you easily send and receive messages to
queues and topics for any message service which implements the JMS
specification.

3. *The publish/subscribe model supports publishing messages to a
particular message topic. Subscribers may register interest in
receiving messages on a particular message topic. In this model,
neither the publisher nor the subscriber knows about each other. A
good analogy for this is an anonymous bulletin board. The following
are characteristics of this model:
• Multiple consumers (or none) receive the message
• There is a timing dependency between publishers and
subscribers. The publisher has to create a message topic for
clients to subscribe.

4. • The subscriber has to remain continuously active to
receive messages, unless it has established a durable subscription. In
that case, messages published while the subscriber is not connected
redistribute when it reconnects.
Example:
JMS Publisher Flow Configuration:
*Open the “jms” message flow and drag and drop an HTTP endpoint
on to the flow. Double-click on the HTTP endpoint to bring up the
properties dialog. Specify “jms_topic” for Path. This will make the
HTTP endpoint accessible using URL
http://localhost:7777/jms_topic.
*Set a payload that you want to add to Publish.

5. *Drag and drop a JMS endpoint next to the HTTP inbound endpoint.
*Double-click the JMS endpoint to bring up the properties dialog.
Specify “topic” for Topic name and Select “Active_MQ” for
Connection Reference in the Connector Configuration that we
created earlier.

6. JMS Subscriber Flow Configuration:
*Use a Jms endpoint to subscribe the Published messages.
*Use a Logger to log the Received Message.
*Use Set-payload to send a response back to the Jms Service.
*Create another Subscriber to receive the same Published
messages.
*The final JMS Subscriber Message Flow is as below:

7. * Run the JMS flow. Open http://localhost:7777/jms_topic.
* This will publish the request to the ActiveMQ JMS Topic “topic”.
* Verify this by examining the ActiveMQ administration page at
http://localhost:8161/admin/topics.jsp. We can see the messages
enqueued, dequeued and the number of consumers.
* The Output you receive after the execution is the Payload Set by
any of the two subscribers JMS-Topic 1 or JMS-Topic2.

8. Example to understand how JMS uses serializing, and
de-serializing objects:
*Serialization is a process of converting an object into a sequence of
bytes which can be persisted to a disk or database or can be sent
through streams. The reverse process of creating object from
sequence of bytes is called deserialization.
Steps to share Objects via JMS are:
1. Open the “jms” message flow and drag and drop an HTTP endpoint
on to the flow. Double-click on the HTTP endpoint to bring up the
properties dialog. Specify “/jms_serializable_queue” for Path. This will
make the HTTP endpoint accessible using URL
http://localhost:7777//jms_serializable_queue.

9. 2. Create a Java Class that implements the Serializable interface as
below:

10. 3. Instantiate the class using Set-payload.
4. Set the values to the object using Expression.

11. 5. Drag and drop a JMS endpoint next to the HTTP inbound endpoint.
*Double-click the JMS endpoint to bring up the properties dialog.
*Specify “serial_queue” for queue name. Select “Active_MQ” for
Connection Reference in the Connector Configuration that we
created earlier.

12. 6. The JMS Client Message Flow is as below:
7. Use a Jms endpoint to receive the messages on the Destination
with the below configuration and Active_MQ is configured before.
8. Use an expression to print the contents of the received payload.

13. 9. Use a Logger to log the Received Message.
10. The final JMS Subscriber Message Flow is as below:

14. *Run the JMS flow. Open
http://localhost:7777/jms_serialiable_queue.
*This will publish the request to the ActiveMQ JMS Topic “topic”.
Verify this by examining the ActiveMQ administration page at
http://localhost:8161/admin/queues.jsp. We can see the messages
enqueued, dequeued and the number of consumers.
*The Output you receive after the execution is the name that is sent
from the Client.
*The Serializable implementation is done in a similar way using Topic
but with many publishers and subscribers.

15. *Thank You All