Dependencies Symfony2
In addition to markymark's answer, you can check if a specific service exists from your controller (or any other container-aware code) with the following snippet:
if ($this->container->has('foo_service.alias')){ // service is loaded and usable}If you're not sure of the exact alias of a given service, or just for kicks and giggles, you can run the console command php app/console container:debug to see all services registered with the container.
You could use class_exists on the main Bundle class that every bundle should have.
For example:
if (class_exists('Acme\CommentBundle\AcmeCommentBundle')){ // Bundle exists and is loaded by AppKernel...}
The Kernel class contains a list of helper methods to check if a certain class is part of an active bundle or if a bundle is registered.
public BundleInterface[] getBundles() Gets the registered bundle instances.public bool isClassInActiveBundle(string $class) Checks if a given class name belongs to an active bundle.