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Chapter 94. Kura

Kura component

Kura component is available starting from Camel 2.15.

This documentation page covers the integration options of Camel with the Eclipse Kura M2M gateway. The common reason to deploy Camel routes into the Eclipse Kura is to provide enterprise integration patterns and Camel components to the messaging M2M gateway. For example you might want to install Kura on Raspberry PI, then read temperature from the sensor attached to that Raspberry PI using Kura services and finally forward the current temperature value to your data center service using Camel EIP and components.

KuraRouter activator

Bundles deployed to the Eclipse Kura are usually developed as bundle activators. So the easiest way to deploy Apache Camel routes into the Kura is to create an OSGi bundle containing the class extending org.apache.camel.kura.KuraRouter class:

public class MyKuraRouter extends KuraRouter {

  @Override
  public void configure() throws Exception {
    from("timer:trigger").
      to("netty-http:http://app.mydatacenter.com/api");
  }

}

Keep in mind that KuraRouter implements the org.osgi.framework.BundleActivator interface, so you need to register its start and stop lifecycle methods while creating Kura bundle component class.

Kura router starts its own OSGi-aware CamelContext. It means that for every class extending KuraRouter, there will be a dedicated CamelContext instance. Ideally we recommend to deploy one KuraRouter per OSGi bundle.

Deploying KuraRouter

Bundle containing your Kura router class should import the following packages in the OSGi manifest:

Import-Package: org.osgi.framework;version="1.3.0",
  org.slf4j;version="1.6.4",
  org.apache.camel,org.apache.camel.impl,org.apache.camel.core.osgi,org.apache.camel.builder,org.apache.camel.model,
  org.apache.camel.component.kura

Keep in mind that you don't have to import every Camel component bundle you plan to use in your routes, as Camel components are resolved as the services on the runtime level.

Before you deploy your router bundle, be sure that you have deployed (and started) the following Camel core bundles (using Kura GoGo shell)...

install file:///home/user/.m2/repository/org/apache/camel/camel-core/2.15.0/camel-core-2.15.0.jar
start <camel-core-bundle-id>
install file:///home/user/.m2/repository/org/apache/camel/camel-core-osgi/2.15.0/camel-core-osgi-2.15.0.jar
start <camel-core-osgi-bundle-id>
install file:///home/user/.m2/repository/org/apache/camel/camel-kura/2.15.0/camel-kura-2.15.0.jar 
start <camel-kura-bundle-id>

...and all the components you plan to use in your routes:

install file:///home/user/.m2/repository/org/apache/camel/camel-stream/2.15.0/camel-stream-2.15.0.jar
start <camel-stream-bundle-id>

Then finally deploy your router bundle:

install file:///home/user/.m2/repository/com/example/myrouter/1.0/myrouter-1.0.jar
start <your-bundle-id>

KuraRouter utilities

Kura router base class provides many useful utilities. This section explores each of them.

SLF4J logger

Kura uses SLF4J facade for logging purposes. Protected member log returns SLF4J logger instance associated with the given Kura router.

public class MyKuraRouter extends KuraRouter {

    @Override
    public void configure() throws Exception {
		log.info("Configuring Camel routes!");
        ...
    }

}

BundleContext

Protected member bundleContext returns bundle context associated with the given Kura router.

public class MyKuraRouter extends KuraRouter {

    @Override
    public void configure() throws Exception {
		ServiceReference<MyService> serviceRef = bundleContext.getServiceReference(LogService.class.getName());
		MyService myService = bundleContext.getService(serviceRef);
        ...
    }

}

CamelContext

Protected member camelContext is the CamelContext associated with the given Kura router.

public class MyKuraRouter extends KuraRouter {

    @Override
    public void configure() throws Exception {
		camelContext.getStatus();
        ...
    }

}

ProducerTemplate

Protected member producerTemplate is the ProducerTemplate instance associated with the given Camel context.

public class MyKuraRouter extends KuraRouter {
 
    @Override
    public void configure() throws Exception {
        producerTemplate.sendBody("jms:temperature", 22.0);
        ...
    }
 
}

ConsumerTemplate

Protected member consumerTemplate is the ConsumerTemplate instance associated with the given Camel context.

public class MyKuraRouter extends KuraRouter {
 
    @Override
    public void configure() throws Exception {
        producerTemplate.sendBody("jms:temperature", 22.0);
        ...
    }
 
}

OSGi service resolver

OSGi service resolver (service(Class<T> serviceType)) can be used to easily retrieve service by type from the OSGi bundle context.

public class MyKuraRouter extends KuraRouter {

    @Override
    public void configure() throws Exception {
		MyService myService = service(MyService.class);
        ...
    }

}

If service is not found, a null value is returned. If you want your application to fail if the service is not available, use requiredService(Class) method instead. The requiredService throws IllegalStateException if a service cannot be found.

public class MyKuraRouter extends KuraRouter {
 
    @Override
    public void configure() throws Exception {
        MyService myService = requiredService(MyService.class);
        ...
    }
 
}

KuraRouter activator callbacks

Kura router comes with the lifecycle callbacks that can be used to customize the way the Camel router works. For example to configure the CamelContext instance associated with the router just before the former is started, override beforeStart method of the KuraRouter class:

public class MyKuraRouter extends KuraRouter {
 
  ...

  protected void beforeStart(CamelContext camelContext) {
    OsgiDefaultCamelContext osgiContext = (OsgiCamelContext) camelContext;
    osgiContext.setName("NameOfTheRouter");
  }

}

Loading XML routes from ConfigurationAdmin

Sometimes it is desired to read the XML definition of the routes from the server configuration. This a common scenario for IoT gateways where over-the-air redeployment cost may be significant. To address this requirement each KuraRouter looks for the kura.camel.BUNDLE-SYMBOLIC-NAME.route property from the kura.camel PID using the OSGi ConfigurationAdmin. This approach allows you to define Camel XML routes file per deployed KuraRouter. In order to update a route, just edit an appropriate configuration property and restart a bundle associated with it. The content of the kura.camel.BUNDLE-SYMBOLIC-NAME.route property is expected to be Camel XML route file, for example:

<routes xmlns="http://camel.apache.org/schema/spring">
    <route id="loaded">
        <from uri="direct:bar"/>
        <to uri="mock:bar"/>
    </route>
</routes>

Deploying Kura router as a declarative OSGi service

If you would like to deploy your Kura router as a declarative OSGi service, you can use the activate and deactivate methods provided by KuraRouter:

<scr:component name="org.eclipse.kura.example.camel.MyKuraRouter" activate="activate" deactivate="deactivate" enabled="true" immediate="true">
  <implementation class="org.eclipse.kura.example.camel.MyKuraRouter"/>
</scr:component>