16.4. Integration with Apache Camel

Overview

Apache Camel provides a simple way to invoke OSGi services using the Bean language. This feature is automatically available whenever a Apache Camel application is deployed into an OSGi container and requires no special configuration.

Registry chaining

When a Apache Camel route is deployed into the OSGi container, the CamelContext automatically sets up a registry chain for resolving bean instances: the registry chain consists of the OSGi registry, followed by the blueprint (or Spring) registry. Now, if you try to reference a particular bean class or bean instance, the registry resolves the bean as follows:
  1. Look up the bean in the OSGi registry first. If a class name is specified, try to match this with the interface or class of an OSGi service.
  2. If no match is found in the OSGi registry, fall back on the blueprint registry (or the Spring registry, if you are using the Spring container).

Sample OSGi service interface

Consider the OSGi service defined by the following Java interface, which defines the single method, getGreeting():
package org.fusesource.example.hello.boston;

public interface HelloBoston {
    public String getGreeting();
}

Sample service export

When defining the bundle that implements the HelloBoston OSGi service, you could use the following blueprint configuration to export the service:
<?xml version="1.0" encoding="UTF-8"?>
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0">

  <bean id="hello" class="org.fusesource.example.hello.boston.HelloBostonImpl"/>
  
  <service ref="hello" interface="org.fusesource.example.hello.boston.HelloBoston"/>

</blueprint>
Where it is assumed that the HelloBoston interface is implemented by the HelloBostonImpl class (not shown).

Invoking the OSGi service from Java DSL

After you have deployed the bundle containing the HelloBoston OSGi service, you can invoke the service from a Apache Camel application using the Java DSL. In the Java DSL, you invoke the OSGi service through the Bean language, as follows:
from("timer:foo?period=5000")
 .bean(org.fusesource.example.hello.boston.HelloBoston.class, "getGreeting")
  .log("The message contains: ${body}")
In the bean command, the first argument is the OSGi interface or class, which must match the interface exported from the OSGi service bundle. The second argument is the name of the bean method you want to invoke. For full details of the bean command syntax, see section "Bean Integration" in "Apache Camel Development Guide".
Note
When you use this approach, the OSGi service is implicitly imported. It is not necessary to import the OSGi service explicitly in this case.

Invoking the OSGi service from XML DSL

In the XML DSL, you can also use the Bean language to invoke the HelloBoston OSGi service, but the syntax is slightly different. In the XML DSL, you invoke the OSGi service through the Bean language, using the method element, as follows:
<beans ...>
  <camelContext xmlns="http://camel.apache.org/schema/spring">
    <route>
      <from uri="timer:foo?period=5000"/>
      <setBody>
          <method ref="org.fusesource.example.hello.boston.HelloBoston"
                  method="getGreeting"/>
      </setBody>
      <log message="The message contains: ${body}"/>
    </route>
  </camelContext>
</beans>
Note
When you use this approach, the OSGi service is implicitly imported. It is not necessary to import the OSGi service explicitly in this case.