Modularization with OSGi Plugins

OSGi (Open Services Gateway initiative) is a framework for developing modular Java applications. OSGi implements a complete and dynamic component model. OSGi components, also called bundles, can be remotely installed, started, stopped, updated, and uninstalled without requiring the OSGi runtime to be restarted. To facilitate dependency management, each OSGi bundle must specify certain details about its Java packages and classes. Bundle life cycle management is implemented via APIs that allow for remote downloading of management policies. The service registry allows bundles to detect the addition of new services, or the removal of services, and adapt accordingly. Liferay 6.2 includes an OSGi runtime in which Liferay plugins that are packaged as OSGi bundles can run. Many Liferay services are available to Liferay’s OSGi runtime and can be invoked from Liferay OSGi plugins. In this tutorial, we explain how to create, package, and deploy custom OSGi plugins for Liferay.

Creating Liferay OSGi Plugins

OSGi web application bundles are usually distributed as JAR files. They’re architecturally similar to standard web application archives. OSGi web application bundles differ from standard web applications archives, however, in that they must include additional metadata that’s required for operating in an OSGi framework. The OSGi specification does not require a specific file extension for web application bundles: web application bundles typically have a .jar extension but a .war extension is also possible.

To create an OSGi plugin for Liferay, you need a Liferay Plugins SDK. You can download a Plugins SDK from www.liferay.com/downloads. Just make sure that the Plugins SDK version matches your Liferay Portal version. Once you’ve extracted the Plugins SDK, navigate to its shared folder. Create a folder for your OSGi plugin project in the shared folder. The name of your project must end in -shared. E.g., create a new folder called my-osgi-liferay-plugin-shared. In your plugin project folder, create two files:

  • bnd.bnd
  • build.xml

Bnd is a tool that makes it easy to create OSGi bundles. See http://bnd.bndtools.org/ for details about what you can specify in your bnd.bnd file. Basically, your bnd.bnd file contains instructions about dependency management and how to create your OSGi bundle’s JAR file.

Your build.xml allows your project to take advantage of the Liferay Plugins SDK’s OSGi plugin support. Add the following code to your build.xml, replacing the value of the <project> element’s name attribute with the name of your plugin:

<?xml version="1.0"?>

<project name="my-osgi-liferay-plugin" basedir="." default="compile">
        <property name="plugin.version" value="1" />

        <import file="../../build-common-osgi-plugin.xml" />
</project>

Your bnd.bnd and build.xml files constitute all the OSGi-specific configuration that’s required! With these files in place, you’re ready to write the rest of your plugin.

Packaging Liferay OSGi Plugins

When you’re ready to package your OSGi bundle, just run ant jar from your plugin project’s root folder (the one with the bnd.bnd and build.mxl files that you created). The bnd .jar in the Plugins SDK reads the instructions in your bnd.bnd file and creates all the files required by OSGi, including the META-INF/MANIFEST.MF. Your plugin is packaged as a JAR file which is created in the Plugins SDK’s dist folder.

Deploying Liferay OSGi Plugins

When you’re ready to deploy your OSGi bundle, make sure that you have the following properties set in your build.[username].properties file in your Plugins SDK’s root folder:

liferay.home=[path-to-your-liferay-installation]
auto.deploy.dir=${liferay.home}/deploy

Once these properties are set, run ant deploy from your plugin project’s root folder. This both packages your bundle and copies it to [Liferay Home]/deploy. Liferay Portal scans the [Liferay Home]/deploy directory for OSGi bundles, as well as for standard Liferay plugins. When it detects an OSGi bundle, it automatically deploys the bundle to [Liferay Home]/data/osgi/modules. Check your log for confirmation that Liferay found and deployed the bundle. You should see a message like this:

18:46:50,653 INFO [com.liferay.portal.kernel.deploy.auto.AutoDeployScanner][AutoDeployDir:204] Processing my-osgi-liferay-plugin-shared-6.2.0.1.jar 18:46:50,655 INFO [com.liferay.portal.kernel.deploy.auto.AutoDeployScanner][ModuleAutoDeployListener:63] Copied module for …/my-osgi-liferay-plugin-shared-6.2.0.1.jar 18:46:50,656 INFO [com.liferay.portal.kernel.deploy.auto.AutoDeployScanner][ModuleAutoDeployListener:69] Module for …/my-osgi-liferay-plugin-shared-6.2.0.1.jar copied successfully. Deployment will start in a few seconds.

Finally, check your [Liferay Home]/data/osgi/modules directory to make sure that your bundle was successfully deployed. To customize Liferay Portal’s module framework, including the OSGi framework’s auto deploy directories, please see the Module Framework sections of Liferay’s portal.properties file: Module Framework Properties. For example, you can set a comma-delimited list of directories to scan for modules to deploy, specify how to often to scan the directories for changes, etc. Remember not to make customizations to the portal.properties file itself but to instead add customized properties to a portal-ext.properties file in your Liferay Home directory.

Related Topics

Plugin Management

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