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OSGi Services Plugin

This bundle plugin is an example of how to add a simple service class that can be used as a proxy by other plugins inside the Felix OSGI container (dotCMS/felix/load)

How to Create a Bundle Plugin with Services#

Let’s review the file organization on the Service (com.dotcms.service) example:

META-INF/MANIFEST.MF: The manifest file is very important for the deployment, it lists the Bundle Name, Version and Packages.

In this MANIFEST you must specify the following (see template plugin- dotCMS/docs/examples/):

  • Bundle-Name: The name of your bundle
  • Bundle-SymbolicName: A short and UNIQUE name for the bundle
  • Bundle-Activator: Package and name of your Activator class (example: com.dotmarketing.osgi.service.Activator)
  • Export-Package: This is a comma separated list of package names. List the packages that you want to make available to other bundles.
  • Import-Package: This is a comma separated list of package names. List the packages that you are using inside the bundle plugin and that are exported by dotCMS.
$ more META-INF/MANIFEST.MF   
Manifest-Version: 1.0  
Bundle-Name: Custom service  
Bundle-SymbolicName: com.dotmarketing.osgi.service  
Bundle-Description: A bundle that creates a custom service  
Bundle-Version: 1.0.0  
Bundle-Activator: com.dotmarketing.osgi.service.Activator  
Export-Package: com.dotmarketing.osgi.service  
Import-Package: org.osgi.framework,  
 com.dotmarketing.osgi

Beware!

In order to work inside the Apache Felix OSGI runtime, the import and export directive must be bi-directional.

dotCMS must declare the set of packages that will be available to the OSGI plugins by changing the file: dotCMS/WEB-INF/felix/osgi-extra.conf.

This is possible also using the dotCMS UI (System -> Dynamic Plugins -> Exported Packages).

Only after exported packages are defined in this list, can a plugin then Import the packages to use them inside the OSGI bundle.

Source#

Under the src folder you will find all the Java classes needed to create a new Service:

$ pwd  
dotCMS/docs/examples/osgi/com.dotcms.service/src/com/dotmarketing/osgi/service  
$ ls -l  
-rw-r--r-- 1  Activator.java  
-rw-r--r-- 1  HelloWorld.java  
-rw-r--r-- 1  HelloWorldService.java

Exposed service#

The exposed service for this example will be a simple Interface class with its implementation (com.dotmarketing.osgi.service.HelloWorld AND com.dotmarketing.osgi.service.HelloWorldService).

Activator#

This bundle activator extends from com.dotmarketing.osgi.GenericBundleActivator and implements BundleActivator.start.

It registers an instance of a our test service using the bundle context; and attaches properties to the service that can be queried when performing a service look-up.

The newly registered service will be used in the example: com.dotcms.servlet.