Chapter 294. Camel SCR (deprecated)

Camel-scr bundle is not included in Apache Camel versions prior 2.15.0, but the artifact itself can be used with any Camel version since 2.12.0.

org.apache.camel/camel-scr bundle provides a base class, AbstractCamelRunner, which manages a Camel context for you and a helper class, ScrHelper, for using your SCR properties in unit tests. Camel-scr feature for Apache Karaf defines all features and bundles required for running Camel in SCR bundles.

AbstractCamelRunner class ties CamelContext’s lifecycle to Service Component’s lifecycle and handles configuration with help of Camel’s PropertiesComponent. All you have to do to make a Service Component out of your java class is to extend it from AbstractCamelRunner and add the following org.apache.felix.scr.annotations on class level:

Add required annotations

@Component
@References({
    @Reference(name = "camelComponent",referenceInterface = ComponentResolver.class,
        cardinality = ReferenceCardinality.MANDATORY_MULTIPLE, policy = ReferencePolicy.DYNAMIC,
        policyOption = ReferencePolicyOption.GREEDY, bind = "gotCamelComponent", unbind = "lostCamelComponent")
})

Then implement getRouteBuilders() method which returns the Camel routes you want to run:

Implement getRouteBuilders()

    @Override
    protected List<RoutesBuilder> getRouteBuilders() {
        List<RoutesBuilder> routesBuilders = new ArrayList<>();
        routesBuilders.add(new YourRouteBuilderHere(registry));
        routesBuilders.add(new AnotherRouteBuilderHere(registry));
        return routesBuilders;
    }

And finally provide the default configuration with:

Default configuration in annotations

@Properties({
   @Property(name = "camelContextId", value = "my-test"),
   @Property(name = "active", value = "true"),
   @Property(name = "...", value = "..."),
   ...
})

That’s all. And if you used camel-archetype-scr to generate a project all this is already taken care of.

Below is an example of a complete Service Component class, generated by camel-archetype-scr:

CamelScrExample.java

// This file was generated from org.apache.camel.archetypes/camel-archetype-scr/2.15-SNAPSHOT
package example;

import java.util.ArrayList;
import java.util.List;

import org.apache.camel.scr.AbstractCamelRunner;
import example.internal.CamelScrExampleRoute;
import org.apache.camel.RoutesBuilder;
import org.apache.camel.spi.ComponentResolver;
import org.apache.felix.scr.annotations.*;

@Component(label = CamelScrExample.COMPONENT_LABEL, description = CamelScrExample.COMPONENT_DESCRIPTION, immediate = true, metatype = true)
@Properties({
    @Property(name = "camelContextId", value = "camel-scr-example"),
    @Property(name = "camelRouteId", value = "foo/timer-log"),
    @Property(name = "active", value = "true"),
    @Property(name = "from", value = "timer:foo?period=5000"),
    @Property(name = "to", value = "log:foo?showHeaders=true"),
    @Property(name = "messageOk", value = "Success: {{from}} -> {{to}}"),
    @Property(name = "messageError", value = "Failure: {{from}} -> {{to}}"),
    @Property(name = "maximumRedeliveries", value = "0"),
    @Property(name = "redeliveryDelay", value = "5000"),
    @Property(name = "backOffMultiplier", value = "2"),
    @Property(name = "maximumRedeliveryDelay", value = "60000")
})
@References({
    @Reference(name = "camelComponent",referenceInterface = ComponentResolver.class,
        cardinality = ReferenceCardinality.MANDATORY_MULTIPLE, policy = ReferencePolicy.DYNAMIC,
        policyOption = ReferencePolicyOption.GREEDY, bind = "gotCamelComponent", unbind = "lostCamelComponent")
})
public class CamelScrExample extends AbstractCamelRunner {

    public static final String COMPONENT_LABEL = "example.CamelScrExample";
    public static final String COMPONENT_DESCRIPTION = "This is the description for camel-scr-example.";

    @Override
    protected List<RoutesBuilder> getRouteBuilders() {
        List<RoutesBuilder> routesBuilders = new ArrayList<>();
        routesBuilders.add(new CamelScrExampleRoute(registry));
        return routesBuilders;
    }
}

CamelContextId and active properties control the CamelContext’s name (defaults to "camel-runner-default") and whether it will be started or not (defaults to "false"), respectively. In addition to these you can add and use as many properties as you like. Camel’s PropertiesComponent handles recursive properties and prefixing with fallback without problem.

AbstractCamelRunner will make these properties available to your RouteBuilders with help of Camel’s PropertiesComponent and it will also inject these values into your Service Component’s and RouteBuilder’s fields when their names match. The fields can be declared with any visibility level, and many types are supported (String, int, boolean, URL, …​).

Below is an example of a RouteBuilder class generated by camel-archetype-scr:

CamelScrExampleRoute.java

// This file was generated from org.apache.camel.archetypes/camel-archetype-scr/2.15-SNAPSHOT
package example.internal;

import org.apache.camel.LoggingLevel;
import org.apache.camel.builder.RouteBuilder;
import org.apache.camel.impl.SimpleRegistry;
import org.apache.commons.lang.Validate;

public class CamelScrExampleRoute extends RouteBuilder {

    SimpleRegistry registry;

    // Configured fields
    private String camelRouteId;
    private Integer maximumRedeliveries;
    private Long redeliveryDelay;
    private Double backOffMultiplier;
    private Long maximumRedeliveryDelay;

    public CamelScrExampleRoute(final SimpleRegistry registry) {
        this.registry = registry;
    }

    @Override
    public void configure() throws Exception {
        checkProperties();

        // Add a bean to Camel context registry
        registry.put("test", "bean");

        errorHandler(defaultErrorHandler()
            .retryAttemptedLogLevel(LoggingLevel.WARN)
            .maximumRedeliveries(maximumRedeliveries)
            .redeliveryDelay(redeliveryDelay)
            .backOffMultiplier(backOffMultiplier)
            .maximumRedeliveryDelay(maximumRedeliveryDelay));

        from("{{from}}")
            .startupOrder(2)
            .routeId(camelRouteId)
            .onCompletion()
                .to("direct:processCompletion")
            .end()
            .removeHeaders("CamelHttp*")
            .to("{{to}}");


        from("direct:processCompletion")
            .startupOrder(1)
            .routeId(camelRouteId + ".completion")
            .choice()
                .when(simple("${exception} == null"))
                    .log("{{messageOk}}")
                .otherwise()
                    .log(LoggingLevel.ERROR, "{{messageError}}")
            .end();
        }
    }

    public void checkProperties() {
        Validate.notNull(camelRouteId, "camelRouteId property is not set");
        Validate.notNull(maximumRedeliveries, "maximumRedeliveries property is not set");
        Validate.notNull(redeliveryDelay, "redeliveryDelay property is not set");
        Validate.notNull(backOffMultiplier, "backOffMultiplier property is not set");
        Validate.notNull(maximumRedeliveryDelay, "maximumRedeliveryDelay property is not set");
    }
}

Let’s take a look at CamelScrExampleRoute in more detail.

    // Configured fields
    private String camelRouteId;
    private Integer maximumRedeliveries;
    private Long redeliveryDelay;
    private Double backOffMultiplier;
    private Long maximumRedeliveryDelay;

The values of these fields are set with values from properties by matching their names.

        // Add a bean to Camel context registry
        registry.put("test", "bean");

If you need to add some beans to CamelContext’s registry for your routes, you can do it like this.

    public void checkProperties() {
        Validate.notNull(camelRouteId, "camelRouteId property is not set");
        Validate.notNull(maximumRedeliveries, "maximumRedeliveries property is not set");
        Validate.notNull(redeliveryDelay, "redeliveryDelay property is not set");
        Validate.notNull(backOffMultiplier, "backOffMultiplier property is not set");
        Validate.notNull(maximumRedeliveryDelay, "maximumRedeliveryDelay property is not set");
    }

It is a good idea to check that required parameters are set and they have meaningful values before allowing the routes to start.

        from("{{from}}")
            .startupOrder(2)
            .routeId(camelRouteId)
            .onCompletion()
                .to("direct:processCompletion")
            .end()
            .removeHeaders("CamelHttp*")
            .to("{{to}}");


        from("direct:processCompletion")
            .startupOrder(1)
            .routeId(camelRouteId + ".completion")
            .choice()
                .when(simple("${exception} == null"))
                    .log("{{messageOk}}")
                .otherwise()
                    .log(LoggingLevel.ERROR, "{{messageError}}")
            .end();

Note that pretty much everything in the route is configured with properties. This essentially makes your RouteBuilder a template. SCR allows you to create more instances of your routes just by providing alternative configurations. More on this in section Using Camel SCR bundle as a template.

In (non-OSGi) unit tests you should use prepare() → run() → stop() instead of activate() → deactivate() for more fine-grained control. Also, this allows us to avoid possible SCR specific operations in tests.

The easiest way to create an Camel SCR bundle project is to use camel-archetype-scr and Maven.

You can generate a project with the following steps:

Generating a project

$ mvn archetype:generate -Dfilter=org.apache.camel.archetypes:camel-archetype-scr
 
Choose archetype:
1: local -> org.apache.camel.archetypes:camel-archetype-scr (Creates a new Camel SCR bundle project for Karaf)
Choose a number or apply filter (format: [groupId:]artifactId, case sensitive contains): : 1
Define value for property 'groupId': : example
[INFO] Using property: groupId = example
Define value for property 'artifactId': : camel-scr-example
Define value for property 'version': 1.0-SNAPSHOT: :
Define value for property 'package': example: :
[INFO] Using property: archetypeArtifactId = camel-archetype-scr
[INFO] Using property: archetypeGroupId = org.apache.camel.archetypes
[INFO] Using property: archetypeVersion = 2.15-SNAPSHOT
Define value for property 'className': : CamelScrExample
Confirm properties configuration:
groupId: example
artifactId: camel-scr-example
version: 1.0-SNAPSHOT
package: example
archetypeArtifactId: camel-archetype-scr
archetypeGroupId: org.apache.camel.archetypes
archetypeVersion: 2.15-SNAPSHOT
className: CamelScrExample
Y: :

Done!

Now run:

mvn install

and the bundle is ready to be deployed.

Service Component is a POJO and has no special requirements for (non-OSGi) unit testing. There are however some techniques that are specific to Camel SCR or just make testing easier.

Below is an example unit test, generated by camel-archetype-scr:

// This file was generated from org.apache.camel.archetypes/camel-archetype-scr/2.15-SNAPSHOT
package example;

import java.util.List;

import org.apache.camel.scr.internal.ScrHelper;
import org.apache.camel.builder.AdviceWithRouteBuilder;
import org.apache.camel.component.mock.MockComponent;
import org.apache.camel.component.mock.MockEndpoint;
import org.apache.camel.model.ModelCamelContext;
import org.apache.camel.model.RouteDefinition;
import org.junit.After;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.TestName;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

@RunWith(JUnit4.class)
public class CamelScrExampleTest {

    Logger log = LoggerFactory.getLogger(getClass());

    @Rule
    public TestName testName = new TestName();

    CamelScrExample integration;
    ModelCamelContext context;

    @Before
    public void setUp() throws Exception {
        log.info("*******************************************************************");
        log.info("Test: " + testName.getMethodName());
        log.info("*******************************************************************");

        // Set property prefix for unit testing
        System.setProperty(CamelScrExample.PROPERTY_PREFIX, "unit");

        // Prepare the integration
        integration = new CamelScrExample();
        integration.prepare(null, ScrHelper.getScrProperties(integration.getClass().getName()));
        context = integration.getContext();

        // Disable JMX for test
        context.disableJMX();

        // Fake a component for test
        context.addComponent("amq", new MockComponent());
    }

    @After
    public void tearDown() throws Exception {
        integration.stop();
    }

    @Test
    public void testRoutes() throws Exception {
        // Adjust routes
        List<RouteDefinition> routes = context.getRouteDefinitions();

        routes.get(0).adviceWith(context, new AdviceWithRouteBuilder() {
            @Override
            public void configure() throws Exception {
                // Replace "from" endpoint with direct:start
                replaceFromWith("direct:start");
                // Mock and skip result endpoint
                mockEndpoints("log:*");
            }
        });

        MockEndpoint resultEndpoint = context.getEndpoint("mock:log:foo", MockEndpoint.class);
        // resultEndpoint.expectedMessageCount(1); // If you want to just check the number of messages
        resultEndpoint.expectedBodiesReceived("hello"); // If you want to check the contents

        // Start the integration
        integration.run();

        // Send the test message
        context.createProducerTemplate().sendBody("direct:start", "hello");

        resultEndpoint.assertIsSatisfied();
    }
}

Now, let’s take a look at the interesting bits one by one.

Using property prefixing

        // Set property prefix for unit testing
        System.setProperty(CamelScrExample.PROPERTY_PREFIX, "unit");

This allows you to override parts of the configuration by prefixing properties with "unit.". For example, unit.from overrides from for the unit test.

Prefixes can be used to handle the differences between the runtime environments where your routes might run. Moving the unchanged bundle through development, testing and production environments is a typical use case.

Getting test configuration from annotations

        integration.prepare(null, ScrHelper.getScrProperties(integration.getClass().getName()));

Here we configure the Service Component in test with the same properties that would be used in OSGi environment.

Mocking components for test

        // Fake a component for test
        context.addComponent("amq", new MockComponent());

Components that are not available in test can be mocked like this to allow the route to start.

Adjusting routes for test

        // Adjust routes
        List<RouteDefinition> routes = context.getRouteDefinitions();

        routes.get(0).adviceWith(context, new AdviceWithRouteBuilder() {
            @Override
            public void configure() throws Exception {
                // Replace "from" endpoint with direct:start
                replaceFromWith("direct:start");
                // Mock and skip result endpoint
                mockEndpoints("log:*");
            }
        });

Camel’s AdviceWith feature allows routes to be modified for test.

Starting the routes

        // Start the integration
        integration.run();

Here we start the Service Component and along with it the routes.

Sending a test message

        // Send the test message
        context.createProducerTemplate().sendBody("direct:start", "hello");

Here we send a message to a route in test.

Once the bundle has been built with mvn install it’s ready to be deployed. To deploy the bundle on Apache Karaf perform the following steps on Karaf command line:

Deploying the bundle in Apache Karaf

# Add Camel feature repository
karaf@root> features:chooseurl camel 2.15-SNAPSHOT
 
# Install camel-scr feature
karaf@root> features:install camel-scr
 
# Install commons-lang, used in the example route to validate parameters
karaf@root> osgi:install mvn:commons-lang/commons-lang/2.6
 
# Install and start your bundle
karaf@root> osgi:install -s mvn:example/camel-scr-example/1.0-SNAPSHOT
 
# See how it's running
karaf@root> log:tail -n 10
 
Press ctrl-c to stop watching the log.

# Override 'messageOk' property
karaf@root> config:propset -p example.CamelScrExample messageOk "This is better logging"

# Create a PID with a tail
karaf@root> config:edit example.CamelScrExample-anotherone
 
# Override some properties
karaf@root> config:propset camelContextId my-other-context
karaf@root> config:propset to "file://removeme?fileName=removemetoo.txt"
 
# Save the PID
karaf@root> config:update

When designing a Service Component to be a template you typically don’t want it to start without a "tailed" configuration i.e. with the default configuration.

To prevent your Service Component from starting with the default configuration add policy = ConfigurationPolicy.REQUIRE `to the class level `@Component annotation.