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Event Message

This page explains how you can implement a sample scenario of Event Message using WSO2 Micro Integrator.

Introduction to Event Message

The Event Message EIP is used for reliable, asynchronous event notifications between applications.

Info

For more information, see the Event Message.

Event message solution

Sample scenario

The example scenario depicts an inventory for stocks and demonstrates how the EIP distributes a message among several subscribers. It includes multiple instances of the subscribers for the event. When a message is sent to the WSO2 MI, it is transmitted to these subscriber instances, each of which acts as a subscriber through the ActiveMQ topic.

The diagram below depicts how to simulate the example scenario using the WSO2 MI.

Event message

Before digging into implementation details, let's take a look at the relationship between the example scenario and the Event Message EIP by comparing their core components.

Event Message EIP Event Message Example Scenario
Subject Stock Quote Client
Event Message ActiveMQ topic
Observer EventObserver Proxies

Synapse configuration of the artifacts

<?xml version="1.0" encoding="UTF-8"?>
<proxy name="EventGeneratorProxy" transports="http" startOnLoad="true" trace="disable" xmlns="http://ws.apache.org/ns/synapse">
   <target>
      <inSequence>
         <property name="OUT_ONLY" value="true" />
         <property name="FORCE_SC_ACCEPTED" value="true" scope="axis2" />
         <call>
           <endpoint>
               <address uri="jms:/SimpleStockQuoteService?transport.jms.ConnectionFactory=myTopicSender"/>
           </endpoint>
         </call>
      </inSequence>
   </target>
</proxy>

<?xml version="1.0" encoding="UTF-8"?>
<proxy name="EventObserver1" transports="jms" startOnLoad="true" trace="disable" xmlns="http://ws.apache.org/ns/synapse">
   <target>
       <inSequence>
          <log category="INFO" level="custom">
              <property name="Observer1" expression="$body" />
          </log>
          <drop/>
        </inSequence>
   </target>
   <parameter name="transport.jms.ContentType">
      <rules>
         <jmsProperty>contentType</jmsProperty>
         <default>application/xml</default>
      </rules>
   </parameter>
   <parameter name="transport.jms.ConnectionFactory">myTopicConnectionFactory</parameter>
   <parameter name="transport.jms.DestinationType">topic</parameter>
   <parameter name="transport.jms.Destination">SimpleStockQuoteService</parameter>
</proxy>

<?xml version="1.0" encoding="UTF-8"?>
<proxy name="EventObserver2" transports="jms" startOnLoad="true" trace="disable" xmlns="http://ws.apache.org/ns/synapse">
    <target>
        <inSequence>
           <log level="custom">
           <property name="Observer2" value="Event received by the Observer2"/>
           </log>
           <log category="INFO" level="custom">
              <property name="Observer2" expression="$body" />
           </log>
           <drop/>
        </inSequence>
    </target>
    <parameter name="transport.jms.ContentType">
        <rules>
           <jmsProperty>contentType</jmsProperty>
           <default>application/xml</default>
        </rules>
    </parameter>
    <parameter name="transport.jms.ConnectionFactory">myTopicConnectionFactory</parameter>
    <parameter name="transport.jms.DestinationType">topic</parameter>
    <parameter name="transport.jms.Destination">SimpleStockQuoteService</parameter>
</proxy>

Set up the sample scenario

  1. Install WSO2 Micro Integrator.

    Info

    Follow the Install the Micro Integrator Runtime documentation for more information.

  2. Launch Visual Studio Code with the Micro Integrator for VS Code extension (MI for VS Code) installed.

    Info

    Follow the Install Micro Integrator for VS Code documentation for a complete installation guide.

  3. Download the artifacts of the sample.

    Download ZIP

  4. Import the artifacts to WSO2 MI.

    Click File -> Open Folder -> Select the extracted ZIP file to import the downloaded ZIP file.

  5. Start the project in the WSO2 MI server.

    For instructions, go to Build and Run Documentation.

  6. Set up and Start ActiveMQ.

Note

Make sure to configure the relevant JMS parameters in the deployment.toml file. 

[[transport.jms.listener]]
name = "myTopicConnectionFactory"
parameter.initial_naming_factory = "org.apache.activemq.jndi.ActiveMQInitialContextFactory"
parameter.provider_url = "tcp://localhost:61616"
parameter.connection_factory_name = "TopicConnectionFactory"
parameter.connection_factory_type = "topic"

[[transport.jms.sender]]
name = "myTopicSender"
parameter.initial_naming_factory = "org.apache.activemq.jndi.ActiveMQInitialContextFactory"
parameter.provider_url = "tcp://localhost:61616"
parameter.connection_factory_name = "TopicConnectionFactory"
parameter.connection_factory_type = "topic"

Execute the sample

Send the following request to the service using SoapUI (or any other SOAP client).

POST http://localhost:8290/services/EventGeneratorProxy

Content-Type: text/xml;charset=UTF-8
SOAPAction: "urn:getQuote"

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ser="http://services.samples" xmlns:xsd="http://services.samples/xsd">
<soapenv:Body>
    <ser:getQuote>
        <ser:request>
            <xsd:symbol>IBM</xsd:symbol>
        </ser:request>
    </ser:getQuote>
</soapenv:Body>
</soapenv:Envelope>

Analyze the output

When you execute the command above, a message is sent to the ActiveMQ topic. Notice the following processed server log in WSO2 MI output:

INFO {LogMediator} - {proxy:EventObserver2} Observer2 = <soapenv:Body xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
      <ser:getQuote xmlns:ser="http://services.samples">    
         <ser:request>          
            <xsd:symbol xmlns:xsd="http://services.samples/xsd">IBM</xsd:symbol>
         </ser:request>
      </ser:getQuote>
   </soapenv:Body>
INFO {LogMediator} - {proxy:EventObserver1} Subscriber1 = <soapenv:Body xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"><soapenv:Envelope xmlns:xsd="http://services.samples/xsd" xmlns:ser="http://services.samples"><soapenv:Body>
      <ser:getQuote>    
         <ser:request>          
            <xsd:symbol>IBM</xsd:symbol>
         </ser:request>
      </ser:getQuote>
   </soapenv:Body></soapenv:Envelope></soapenv:Body>