Java Reference
In-Depth Information
As we mentioned, a bundle can be in different states. The lifecycle layer defines the
following six states:
■
INSTALLED
: The bundle has been installed in the
OSG
i container.
■
RESOLVED
: All package requirements are fulfilled and the bundle is ready to
be started.
■
STARTING
: The bundle is in the process of starting.
■
ACTIVE
: The bundle has started.
■
STOPPING
: The bundle is in the process of stopping. After this, the bundle will
be in the
RESOLVED
state.
■
UNINSTALLED
:
OSG
i has removed the bundle from the container.
It may seem a bit confusing now, but the example we provide will clear things up, so
let's move on and implement our first
OSG
i service.
16.2
Our first OSGi service
In the first chapter of the topic, we implemented a simple calculator application.
That application was simple enough to demonstrate the basic concepts of unit test-
ing. We take the same approach in this chapter. We implement the calculator
application as an
OSG
i service. We also implement a sample client for that service
and a test bundle for the client. Finally, we install the three bundles in the Apache
Felix environment.
Apache Felix—open source implementation of the service platform
The OSGi alliance defines a number of specifications for the OSGi service plat-
form. The implementation of these specifications can be done by anyone. In this
chapter, we use the Apache Software Foundation implementation Apache Felix
(
http://felix.apache.org/). Th
e installation of the Felix project is easy. Start by
downloading the latest distribution. Extract the archive and create an environ-
ment variable called
FELIX_HOME
pointing to the Felix folder. The Felix folder
should contain the following:
■
bin—This folder contains only one JAR file, called felix.jar. This JAR is used to
instantiate the Felix console to remotely operate the different services.
■
bundle—This folder contains the various Felix bundles.
■
conf—This folder contains the Felix configuration file.
■
doc—This folder contains the documentation.
The implementation of our calculator service starts with the interface in listing 16.1.
Every
OSG
i service is defined by an interface.
