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Anchortop
top Enterprise messaging has become an increasingly important component of loosely coupled, reliable enterprise frameworks. This is due in large part to the proliferation of enterprise applications and disparate enterprise resources, and the increasing need to integrate these applications into cohesive systems. Over the years Messaging and Message Oriented Middleware (MOM) has provided this integration proprietary manner. Introduction of Java Messaging Service (JMS) as a standard, eliminated many of the disadvantages in proprietary MOM based products. In addition,Message Driven Beans(MDBs) introduced together with Enterprise Java Beans 2.0 have served to get the best out of existing investments in J2EE application servers. Most of the J2EE application servers in modern era are acting as a MOM with a whole lot of value added services to JMS. As a J2EE 1.4 certified application server, Apache Geronimo comes into the party with support of JMS integrating with one of the best breed open source messaging frameworks, ActiveMQ. This article will provide you with a way to use JMS for your enterprise application scenario both as a local and remotely referred environments with Geronimo and ActiveMQ.

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Overview of JMS in Geronimo/ActiveMQ Enviroment Anchor overviewoverview

Geronimo server comes with a JMS server and application components that can access JMS resources like connection factories, topics and queues from it. This JMS server is also known as message broker. The default message broker supported by Geronimo is ActiveMQ, usually does not need to be changed since it is a mature and feature-rich JMS product. This implementation uses inbuilt Derby database for the message persistent features.

ActiveMQ supports a large variety of transports (such as TCP, SSL, UDP, multicast, intra-JVM, and NIO) and client interactions (such as push, pull, and publish/subscribe). In the Geronimo context ActiveMQ supports MDBs, which are EJBs that consume JMS messages. It allows JMS applications to take J2EE specific features from Geronimo and application components such as JSPs, Servlets or EJBs utilizing JMS. Geronimo has implemented this JMS API in an abstract layer to support any JMS provider. It has achieved this feature by supporting J2EE Connector (JCA) specification. The JCA 1.5 specification details the contracts required between the application server and the driver supplied by ActiveMQ (resource adapter). Applications deployed in the Geronimo access ActiveMQ message broker only through this resource adapter(RA).

Application Overview Anchor applicationapplication

Order processing application has two defined message queues to receive orders and consignments. Order requests can be generated and sent via the company's web application. When order requests are received to the order queue, a MDB will be triggered. It will carry out the next level of order request processing by saving those requests in to a server repository. Those saved order requests will be processed by a company employee later.

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The core of the order placement application will be deployed as an EAR to the application server. Overview of the contents of EAR is given in the following depiction.

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MDB Implementation

The Message-Driven Bean uses the @MessageDriven annotation to replace the declaration of this MDB in the ejb-jar.xml file. By providing the annotation with further information it knows to look for a destination (in this case it happens to be a queue) to process. So this MDB will sit there and process messages passed into the 'OrderQueue.' The end result is that is echoes this message to the screen.

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In this application there is a MDB that will listen on OrderQueue. openejb-jar.xml tells Geronimo that there is a MDB which is associated with the jms-resources JMS Resource Group. It links OrderRecvMDB with OrderQueue via CommonConnectionFactory.

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geronimo-application.xml and application.xml define the main components of the EAR. Both EJB component and Web archive information are given in these files as usual.  This geronimo-application.xml also includes a section for defining a JMS queue and a common queue connection factory to access it. This is used for deploying the geronimo-activemq-ra.rar that is embedded in the ear.

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Client Implementation

The OrderSenderServlet.java servlet will parse the web form, create a message, and send that message to the OrderQueue via the CommonConnectoryFactory.

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Please note that Geronimo ignores the 'mappedName' configuration attribute for @Resource. Instead, use 'name' when annotating.

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web.xml of the archive has the relevant configurations for the both queue connection factory and the queue, which is essential to refer to resources in a local enviroment.

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Please note that this web application supports Servlet 2.5 specification. Some of the configurations in older versions (2.4) are slightly different than given in the above web.xml.

geronimo-web.xml is not necessary in this case as the annotations will help resolve the queue or connection factory references.

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Configuring, Building and Deploying the Sample Application Anchorconfigureconfigure

Download the order processing application from the following link:
jms-mdb-sample

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Testing of the Sample Application Anchor testingtesting

To test the sample web application open a browser and type http://localhost:8080/order. It will forward you in to the Order Management Welcome page. Then user has to fill the necessary information for the order placement and submit it.

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After processing an order you will see the message printed to your console.

Summary Anchorsummarysummary

This article has demonstrated the use of JMS features in Apache Geronimo with the ActiveMQ JMS server. It provides a hypothetical example which extensively used JMS features.

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