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.
