Saturday, November 17, 2012

Camel File Poller and JMS Consumer in Scala

I put the code on  GitHub:

In this tutorial, I'm going to demonstrate using Apache Camel to write a Scala file poller. When a file arrives in the "incoming" directory, I'm placing a JMS message onto a queue. Lastly, I'll have a JMS consumer written in Scala that will receive the message from the queue. I'll be using ActiveMQ as my JMS message broker. The main focal point in the tutorial is using Apache Camel for creating a file poller. I'm not doing anything special with ActiveMQ and the JMS consumer could just as easily have been written in Java. I just chose to use Scala, because I like it for its expressiveness.

I won't go through the steps of setting up the architecture. I'll cover that in a future tutorial. For now, I assume you have ActiveMQ running, the Camel JARs downloaded, and your Scala development environment ready to go. Now on to the code.

There are only two Scala classes needed. The first component is the Scala class that defines our Camel routes. We have a single route that routes incoming files to a JMS consumer. Here's our Camel route definition in Scala.

import org.apache.camel.scala.dsl.builder.RouteBuilder
import org.apache.camel.model.dataformat.BindyType

class JmsRoutes extends RouteBuilder {
    "file://incoming" --> "activemq:queue:test.queue"

The second component in the application is the JMS consumer. This consumer simply blocks, waiting for a file to arrive in a directory named "incoming". Here's the code for the JMS message consumer.

import javax.jms.ConnectionFactory
import org.apache.camel.CamelContext
import org.apache.camel.ConsumerTemplate
import org.apache.camel.impl.DefaultCamelContext
import org.apache.camel.component.jms.JmsComponent
import org.apache.activemq.ActiveMQConnectionFactory

object JmsConsumer {
    def main(args : Array[String]) {
        val connectionFactory = new ActiveMQConnectionFactory("vm://localhost?broker.persistent=false")
        val context = new DefaultCamelContext()

        context.addComponent("activemq", JmsComponent.jmsComponentAutoAcknowledge(connectionFactory))

        context.addRoutes(new JmsRoutes())

        val consumerTemplate = context.createConsumerTemplate()


        println("received message")

This shows how simple it is to use Camel for routing messages in a Scala application. I like the expressiveness of the routing syntax. Camel is a very powerful integration framework, and yet it's extremely easy to use.

No comments:

Post a Comment