Chapter 6. Running Apache Camel application in Spring Boot

Every Camel Spring Boot application must use the dependencyManagement element in the project’s pom.xml to specify the productized versions of the dependencies. These dependencies are defined in the Red Hat Fuse BOM and are supported for the specific version of Red Hat Fuse. You can omit the version number attribute for the additional starters so as not to override the versions from BOM. See quickstart pom for more information.

<dependencyManagement>
	<dependencies>
		<dependency>
			<groupId>org.jboss.redhat-fuse</groupId>
			<artifactId>fuse-springboot-bom</artifactId>
			<version>${fuse.version}</version>
			<type>pom</type>
			<scope>import</scope>
		</dependency>
	</dependencies>
</dependencyManagement>

Starters are the Apache Camel modules that are intended to be used in Spring Boot applications. There is a camel-xxx-starter module for each Camel component (with a few exceptions listed in the Section 6.3, “List of the Camel components that do not have starter modules” section).

Starters meet the following requirements:

Each starter has its own integration test in tests/camel-itest-spring-boot, that verifies the compatibility with the current release of Spring Boot.

The following components do not have starter modules because of compatibility issues:

Apache Camel provides a starter module that allows you to quickly get started developing Spring Boot applications.

Camel Spring Boot auto-configuration provides a CamelContext instance and creates a SpringCamelContext. It also initializes and performs shutdown of that context. This Camel context is registered in the Spring application context under camelContext bean name and you can access it like other Spring bean. You can access the camelContext as shown below.

@Configuration
public class MyAppConfig {

  @Autowired
  CamelContext camelContext;

  @Bean
  MyService myService() {
    return new DefaultMyService(camelContext);
  }

}

Camel auto-configuration collects all the RouteBuilder instances from the Spring context and automatically injects them into the CamelContext. This simplifies the process of creating a new Camel route with the Spring Boot starter. You can create the routes as follows:

@Component
public class MyRouter extends RouteBuilder {

  @Override
  public void configure() throws Exception {
    from("jms:invoices").to("file:/invoices");
  }

}

Or create a new route RouteBuilder bean in your @Configuration class.

@Configuration
public class MyRouterConfiguration {

  @Bean
  RoutesBuilder myRouter() {
    return new RouteBuilder() {

      @Override
      public void configure() throws Exception {
        from("jms:invoices").to("file:/invoices");
      }

    };
  }
 
}

Spring Boot auto-configuration connects to the Spring Boot external configuration such as properties placeholders, OS environment variables, or system properties with Camel properties support.

To perform operations on the CamelContext bean created by Camel Spring Boot auto-configuration, register a CamelContextConfiguration instance in your Spring context.

The CamelContextConfiguration and beforeApplicationStart(CamelContext) methods are called before the Spring context is started, so the CamelContext instance that is passed to this callback is fully auto-configured. You can add many instances of CamelContextConfiguration into your Spring context and all of them will be executed.

To disable JMX in the auto-configured CamelContext, you can use the camel.springboot.jmxEnabled property as JMX is enabled by default.

Camel auto-configuration provides pre-configured ConsumerTemplate and ProducerTemplate instances. You can inject them into your Spring-managed beans.

@Component
public class InvoiceProcessor {

  @Autowired
  private ProducerTemplate producerTemplate;

  @Autowired
  private ConsumerTemplate consumerTemplate;
  public void processNextInvoice() {
    Invoice invoice = consumerTemplate.receiveBody("jms:invoices", Invoice.class);
    ...
    producerTemplate.sendBody("netty-http:http://invoicing.com/received/" + invoice.id());
  }

}

By default consumer templates and producer templates come with the endpoint cache sizes set to 1000. You can change these values by setting the following Spring properties to the desired cache size, for example:

camel.springboot.consumerTemplateCacheSize = 100
camel.springboot.producerTemplateCacheSize = 200

Camel auto-configuration registers a TypeConverter instance named typeConverter in the Spring context.

@Component
public class InvoiceProcessor {

  @Autowired
  private TypeConverter typeConverter;

  public long parseInvoiceValue(Invoice invoice) {
    String invoiceValue = invoice.grossValue();
    return typeConverter.convertTo(Long.class, invoiceValue);
  }

}

Spring consist of a powerful type conversion API. Spring API is similar to the Camel type converter API. Due to the similarities between the two APIs Camel Spring Boot automatically registers a bridge converter (SpringTypeConverter) that delegates to the Spring conversion API. This means that out-of-the-box Camel will treat Spring Converters similar to Camel.

This allows you to access both Camel and Spring converters using the Camel TypeConverter API, as shown below:

@Component
public class InvoiceProcessor {

  @Autowired
  private TypeConverter typeConverter;

  public UUID parseInvoiceId(Invoice invoice) {
    // Using Spring's StringToUUIDConverter
    UUID id = invoice.typeConverter.convertTo(UUID.class, invoice.getId());
  }

}

Here, Spring Boot delegates conversion to the Spring’s ConversionService instances available in the application context. If no ConversionService instance is available, Camel Spring Boot auto-configuration creates an instance of ConversionService.

To disable the Camel Spring Boot type conversion features, set the camel.springboot.typeConversion property to false. When this property is set to false, the auto-configuration does not register a type converter instance and does not enable the delegation of type conversion to the Spring Boot type conversion API.

By default, the Camel Spring Boot component auto-detects and includes the Camel XML routes that are in the classpath in the camel directory. You can configure the directory name or disable this feature using the configuration option.

camel.springboot.name = MyCamel
camel.springboot.stream-caching-enabled=true

The Camel Spring Boot component auto-detects and embeds the Camel Rest-DSL XML routes that are added in the classpath under the camel-rest directory. You can configure the directory name or disable this feature using the configuration option.

When Camel runs on the Spring Boot, Spring Boot automatically embeds Camel and all its routes, which are annotated with @Component. When testing with Spring Boot use @SpringBootTest instead of @ContextConfiguration to specify which configuration class to use.

When you have multiple Camel routes in different RouteBuilder classes, the Camel Spring Boot component automatically embeds all these routes when running the application. Hence, when you wish to test routes from only one RouteBuilder class you can use the following patterns to include or exclude which RouteBuilders to enable:

Fuse uses external messaging brokers. See Supported Configurations for more information about the supported broker, client and Camel component combinations.

The Camel component must be connected to the JMS connection-factory. The example below shows how to connect the camel-amqp component to a JMS connection-factory.

import org.apache.activemq.jms.pool.PooledConnectionFactory;
import org.apache.camel.component.amqp.AMQPComponent;
import org.apache.qpid.jms.JmsConnectionFactory;
...

AMQPComponent amqpComponent(AMQPConfiguration config) {
       JmsConnectionFactory qpid = new JmsConnectionFactory(config.getUsername(), config.getPassword(), "amqp://"+ config.getHost() + ":" + config.getPort());
       qpid.setTopicPrefix("topic://");

       PooledConnectionFactory factory = new PooledConnectionFactory();
       factory.setConnectionFactory(qpid);

AMQPComponent amqpcomp = new AMQPComponent(factory);