JMS supports two models for messaging as follows:
- Queues: point-to-point
- Topics: publish and subscribe
There are many business use cases that can be implemented using the publisher-subscriber (pub-sub) pattern. For example, consider a blog with subscribed readers. The blog author posts a blog entry that the subscribers of the blog can view. In other words, the blog author publishes a message (the blog post content) and the subscribers (the blog readers) receive that message. Popular publisher/subscriber patterns like these can be implemented using JMS topics as described in the following sections:
In this sample scenario, you create a JMS topic in a broker server such as ActiveMQ or the Message Broker Profile of WSO2 Enterprise Integrator (WSO2 EI), and then you add proxy services using the ESB Profile of WSO2 EI to act as the publisher and subscribers. This example assumes you have already downloaded and installed the ESB Profile of WSO2 EI (see Installation Guide).
Configuring the broker server
For this example, you will use ActiveMQ as the broker server. Follow the instructions in Configure with ActiveMQ to set up the ESB Profile of WSO2 EI with ActiveMQ as the broker.
Configuring the publisher
<EI_HOME>/conf/JNDI.propertiesfile and specify the JNDI designation of the topic (in this example it is
Next, add a proxy service named
StockQuoteProxyand configure it to publish to the topic
SimpleStockQuoteService. You can add the proxy service to the ESB either by building the proxy service in the design view via the Management Console of the ESB Profile or by copying the XML configuration into the source view. Alternatively, you can add an XML file named
<EI_HOME>/repository/deployment/server/synapse-configs/default/proxy-services. A sample XML code segment that defines the proxy service is given below. You will see that the address URI specifies properties to configure the JMS transport.
If you are using the Management Console source view, you must use '&' instead of '&' in endpoint URLs, as shown in the example above. If you are saving this proxy service configuration as an XML file in the
<EI_HOME>/repository/deployment/server/synapse-configs/default/proxy-servicesdirectory, use '&' instead.
Configuring the subscribers
Next, you need to configure two proxy services that subscribe to the JMS topic
SimpleStockQuoteService, so that whenever the topic receives a message, it is sent to the subscribing proxy services. Following is the sample configuration for the proxy services:
Publishing to the topic
Open a command prompt (or a shell in Linux), go to the
<EI_HOME>\bindirectory and execute one of the following commands to start the ESB Profile of WSO2 EI:
- On Windows:
On Linux/Mac OS:
- On Windows:
A log message similar to the following will appear:
To invoke the publisher, use the sample
stock quoteclient service by navigating to the
<EI_HOME>/samples/axis2Clientdirectory and running the following command:
The message flow is executed as follows:
stockquoteclient sends the message to the StockQuoteProxy service, the publisher is invoked and sends the message to the JMS topic.
- The topic delivers the message to all the subscribers of that topic. In this case, the subscribers are ESB proxy services.