Creating our own custom Karaf command using a Maven archetype

The ingredients of this recipe include the Apache Karaf distribution kit, access to JDK, Maven, and a source code editor. The sample code for this recipe is available at https://github.com/jgoodyear/ApacheKarafCookbook/tree/master/chapter1/chapter1-recipe2.

The Maven archetype generates the POM build file, Java code, and Blueprint file for your custom command. Let's take a look at these key components.

The generated POM file contains all of the essential dependencies a Karaf command requires and sets up a basic Maven Bundle Plugin configuration. Edit this file to bring in additional libraries your command requires. Make sure that you update your bundle's build parameters accordingly. When this project is built, a bundle will be produced that can be installed directly into Karaf.

Our custom command logic resides in the generated Java source file, which will be named after the command name you supplied. The generated command extends Karaf's OSGICommandSupport class, which provides us with access to the underlying command session and OSGi environment. A Command annotation adorns our code. This provides the runtime with the scope, name, and description. Karaf provides the Argument and Option annotations to simplify adding a command-line argument and option processing.

The Blueprint container wires together our command implementation to the commands available in Karaf's console.

Thanks to Apache Karaf's SSHD service and remote client, your custom commands can be leveraged to provide external command and control of your applications. Just pass your command and its parameters to the remote client and monitor the returned results.