Developing Applications with Camel Quarkus
TECHNOLOGY PREVIEW - Developing applications with Camel Quarkus
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Preface
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Chapter 1. Introduction to developing applications with Camel Quarkus
This guide is for developers writing Camel applications on top of Quarkus.
Camel components which are supported on Camel Quarkus have an associated Camel Quarkus extension. For more information about the Camel Quarkus extensions supported in this distribution, see the Camel Extensions for Quarkus reference guide.
Camel Quarkus is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production.
These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process. For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview.
Chapter 2. Dependency management
A specific Camel Quarkus release is supposed to work only with a specific Quarkus release.
2.1. Quarkus BOM
The core Quarkus dependencies are managed via com.redhat.quarkus.quarkus:quarkus-bom
. This BOM does not manage the additional Quarkus extensions (for example Camel Quarkus or Kubernetes), so there are other BOMs available for you to use in your projects that contain import quarkus-bom
.
BOM stands for "Bill of Materials" - it is a pom.xml
whose main purpose is to manage the versions of artifacts so that end users importing the BOM in their projects do not need to care which particular versions of the artifacts are supposed to work together. In other words, having a BOM imported in the <depependencyManagement>
section of your pom.xml
allows you to avoid specifying versions for the dependencies managed by the given BOM.
2.2. Camel Quarkus BOM
As long as you do not plan to use any dependencies beyond those from Quarkus and Camel Quarkus, you should use org.apache.camel.quarkus:camel-quarkus-bom
which manages all supported Camel artifacts and imports com.redhat.quarkus.quarkus:quarkus-bom
.
For this technology preview, do not use com.redhat.quarkus:quarkus-universe-bom
as it does not contain the supported Camel extensions included in this release.
2.3. Combining with other BOMs
When combining camel-quarkus-bom
with any other BOM, think carefully in which order you import them, because the order of imports defines the precedence.
For example, if my-foo-bom
is imported before camel-quarkus-bom
then the artifact versions defined in my-foo-bom
will take the precedence. This may or may not be what you intend, depending on whether or not there are any overlapping actifacts in your my-foo-bom
and camel-quarkus-bom
. Additionally, you may also need to consider if those artifact versions in my-foo-bom
with a higher precedence are compatible with the rest of the artifacts managed in camel-quarkus-bom
.
Chapter 3. Defining Camel routes
Camel Quarkus supports the Java DSL language to define Camel Routes.
3.1. Java DSL
Extending org.apache.camel.builder.RouteBuilder
and using the fluent builder methods available there is the most common way of defining Camel Routes. Here is a simple example of a route using the timer component:
import org.apache.camel.builder.RouteBuilder; public class TimerRoute extends RouteBuilder { @Override public void configure() throws Exception { from("timer:foo?period=1000") .log("Hello World"); } }
3.1.1. Endpoint DSL
Since Camel 3.0, you can use fluent builders also for defining Camel endpoints. The following is equivalent with the previous example:
import org.apache.camel.builder.RouteBuilder; import static org.apache.camel.builder.endpoint.StaticEndpointBuilders.timer; public class TimerRoute extends RouteBuilder { @Override public void configure() throws Exception { from(timer("foo").period(1000)) .log("Hello World"); } }
Builder methods for all Camel components are available via camel-quarkus-core
, but you still need to add the given component’s extension as a dependency for the route to work properly. In case of the above example, it would be camel-quarkus-timer
.
Chapter 4. Configuration
Camel Quarkus automatically configures and deploys a Camel Context bean which by default is started/stopped according to the Quarkus Application lifecycle. The configuration step happens at build time during Quarkus' augmentation phase and it is driven by the Camel Quarkus extensions which can be tuned using Camel Quarkus specific quarkus.camel.*
properties.
quarkus.camel.*
configuration properties are documented on the individual extension pages - see e.g. Camel Quarkus Core.
After the configuration is done, a minimal Camel Runtime is assembled and started in the RUNTIME_INIT phase.
4.1. Configuring Camel components
4.1.1. application.properties
To configure components and other aspects of Apache Camel through properties, make sure that your application depends on camel-quarkus-core
directly or transitively. Because most Camel Quarkus extensions depend on camel-quarkus-core
, you typically do not need to add it explicitly.
camel-quarkus-core
brings functionalities from Camel Main to Camel Quarkus.
In the example below, you set a specific ExchangeFormatter
configuration on the LogComponent
via application.properties
:
camel.component.log.exchange-formatter = #class:org.apache.camel.support.processor.DefaultExchangeFormatter camel.component.log.exchange-formatter.show-exchange-pattern = false camel.component.log.exchange-formatter.show-body-type = false
4.1.2. CDI
You can also configure a component programmatically using CDI.
The recommended method is to observe the ComponentAddEvent
and configure the component before the routes and the CamelContext
are started:
import javax.enterprise.context.ApplicationScoped; import javax.enterprise.event.Observes; import org.apache.camel.quarkus.core.events.ComponentAddEvent; import org.apache.camel.component.log.LogComponent; import org.apache.camel.support.processor.DefaultExchangeFormatter; @ApplicationScoped public static class EventHandler { public void onComponentAdd(@Observes ComponentAddEvent event) { if (event.getComponent() instanceof LogComponent) { /* Perform some custom configuration of the component */ LogComponent logComponent = ((LogComponent) event.getComponent()); DefaultExchangeFormatter formatter = new DefaultExchangeFormatter(); formatter.setShowExchangePattern(false); formatter.setShowBodyType(false); logComponent.setExchangeFormatter(formatter); } } }
4.1.2.1. Producing a @Named
component instance
Alternatively, you can create and configure the component yourself in a @Named
producer method. This works as Camel uses the component URI scheme to look-up components from its registry. For example, in the case of a LogComponent
Camel looks for a log
named bean.
Please note that while producing a @Named
component bean will usually work, it may cause subtle issues with some components.
Camel Quarkus extensions may do one or more of the following:
- Pass custom subtype of the default Camel component type. See the Vert.x WebSocket extension example.
- Perform some Quarkus specific customization of the component. See the JPA extension example.
These actions are not performed when you produce your own component instance, therefore, configuring components in an observer method is the recommended method.
import javax.enterprise.context.ApplicationScoped;
import javax.inject.Named;
import org.apache.camel.component.log.LogComponent;
import org.apache.camel.support.processor.DefaultExchangeFormatter;
@ApplicationScoped
public class Configurations {
/**
* Produces a {@link LogComponent} instance with a custom exchange formatter set-up.
*/
@Named("log") 1
LogComponent log() {
DefaultExchangeFormatter formatter = new DefaultExchangeFormatter();
formatter.setShowExchangePattern(false);
formatter.setShowBodyType(false);
LogComponent component = new LogComponent();
component.setExchangeFormatter(formatter);
return component;
}
}
- 1
- The
"log"
argument of the@Named
annotation can be omitted if the name of the method is the same.
4.2. Configuration by convention
In addition to support configuring Camel through properties, camel-quarkus-core
allows you to use conventions to configure the Camel behavior. For example, if there is a single ExchangeFormatter
instance in the CDI container, then it will automatically wire that bean to the LogComponent
.
Chapter 5. Contexts and Dependency Injection (CDI) in Camel Quarkus
CDI plays a central role in Quarkus and Camel Quarkus offers a first class support for it too.
You may use @Inject
, @ConfigProperty
and similar annotations e.g. to inject beans and configuration values to your Camel RouteBuilder
, for example:
import javax.enterprise.context.ApplicationScoped; import javax.inject.Inject; import org.apache.camel.builder.RouteBuilder; import org.eclipse.microprofile.config.inject.ConfigProperty; @ApplicationScoped 1 public class TimerRoute extends RouteBuilder { @ConfigProperty(name = "timer.period", defaultValue = "1000") 2 String period; @Inject Counter counter; @Override public void configure() throws Exception { fromF("timer:foo?period=%s", period) .setBody(exchange -> "Incremented the counter: " + counter.increment()) .to("log:cdi-example?showExchangePattern=false&showBodyType=false"); } }
- 1
- The
@ApplicationScoped
annotation is required for@Inject
and@ConfigProperty
to work in aRouteBuilder
. Note that the@ApplicationScoped
beans are managed by the CDI container and their life cycle is thus a bit more complex than the one of the plainRouteBuilder
. In other words, using@ApplicationScoped
inRouteBuilder
comes with some boot time penalty and you should therefore only annotate yourRouteBuilder
with@ApplicationScoped
when you really need it. - 2
- The value for the
timer.period
property is defined insrc/main/resources/application.properties
of the example project.
Please refer to the Quarkus Dependency Injection guide for more details.
5.1. Accessing CamelContext
To access CamelContext
just inject it into your bean:
import javax.inject.Inject; import javax.enterprise.context.ApplicationScoped; import java.util.stream.Collectors; import java.util.List; import org.apache.camel.CamelContext; @ApplicationScoped public class MyBean { @Inject CamelContext context; public List<String> listRouteIds() { return context.getRoutes().stream().map(Route::getId).sorted().collect(Collectors.toList()); } }
5.2. CDI and the Camel Bean component
5.2.1. Refer to a bean by name
To refer to a bean in a route definition by name, just annotate the bean with @Named("myNamedBean")
and @ApplicationScoped
. The @RegisterForReflection
annotation is important for the native mode.
import javax.enterprise.context.ApplicationScoped; import javax.inject.Named; import io.quarkus.runtime.annotations.RegisterForReflection; @ApplicationScoped @Named("myNamedBean") @RegisterForReflection public class NamedBean { public String hello(String name) { return "Hello " + name + " from the NamedBean"; } }
Then you can use the myNamedBean
name in a route definition:
import org.apache.camel.builder.RouteBuilder; public class CamelRoute extends RouteBuilder { @Override public void configure() { from("direct:named") .to("bean:namedBean?method=hello"); } }