Example 8 - Spell Checker Service using Service Binder

Wiki Markup_\[Note: The Service Binder was the original project to attempt to automate service dependency management for the OSGi platform and was the inspiration for Declarative Services introduced in OSGi R4. The Service Binder is not no longer under active development, but this example is kept in the tutorial for historical purposes. New projects should consider using one of the other dependency injection technologies (e.g., Declarative Services, Dependency Manager, or iPOJO).]_

The purpose of this example is to re-implement the spell checker service in Example 6, but to do so using the Service Binder; to complete this, we must download the Service Binder bundle. The Service Binder bundle is needed to compile the example and at run time to execute the example.

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We specify which class is used to activate the bundle via the Bundle-Activator attribute and also specify that the bundle imports the spell checker, dictionary, and Service Binder packages. (Note: Make sure your manifest file ends in a trailing carriage return or else the last line will be ignored.)

To compile the source code, we must include the felix.jar file (found in Felix' lib directory), the servicebinder.jar file, the example2.jar file, and the example6.jar file in the class path. We compile the source file using a command like:

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To run Felix, we follow the instructions described in usage.html. When we start Felix, it asks for a profile name, we will put all of our bundles in a profile named tutorial. After running Felix, we should stop all tutorial bundles except for the service bundles. Use the ps lb command to make sure that only the bundles from Example 2 and Example 2b are active; use the start and stop commands as appropriate to start and stop the various tutorial bundles, respectively. (Note: Felix uses some bundles to provide its command shell, so do not stop these bundles.) We must also install the servicebinder.jar bundle that we downloaded at the beginning of this example. Assuming that we saved the bundle in our tutorial directory, we install the bundle using the following command:

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The above command installs and starts the bundle in a single step; it is also possible to install and start the bundle in two steps by using the Felix install and start shell commands. To stop the bundle, use the Felix stop shell command. Use the Felix shell ps lb command to get the bundle identifier number for the spell checker service bundle to stop and restart it at will using the stop and start commands, respectively. Using the services command, we can see which services are currently available in the OSGi framework, including our dictionary and spell checker services. We can experiment with our spell checker service's dynamic availability by stopping the dictionary service bundles; when both dictionary services are stopped, the services command will reveal that our bundle is no longer offering its spell checker service. Likewise, when the dictionary services comeback, so will our spell checker service. This bundle will work with the spell checker client bundle that we created in Example 7, so feel free to experiment. To exit Felix, use the shutdown command.unmigrated-wiki-markup

_\[Note: The spell checker client bundle in Example 7 could also be re-implemented using the Service Binder approach outlined in this example. The spell checker client has a one-to-one, dynamic service dependency on the spell checker service. Further, an entire application of instances could be described in a single {{metadata.xml}} in a single bundle or across a collection of bundles and the Service Binder will automatically manage the service dependencies among them.]_