WebSphere Application Server V8.5 Administration and Configuration Guide for the Full Profile

922 WebSphere Application Server V8.5 Administration and Configuration Guide for the Full Profile

26.1 OSGi overview

Open Services Gateway initiative (OSGi) is a framework based on Java technology. OSGi

enables you to write modular, dynamic, and versioning applications. WebSphere Application

Server V8.5 uses the Eclipse Equinox as the framework for OSGi applications and OSGi

V4.2.

You can design and build applications from coherent, versioned, reusable OSGi modules that

are accessed only through well-defined interfaces. The new features of WebSphere

Application Server V8.5 support for OSGi applications includes the following list:

 An OSGi application can contain Enterprise JavaBean (EJB) that allows direct access and

invokes an enterprise bean.

 A blueprint configuration file can specify a user role for security access to the methods of

the bean.

The OSGi framework in WebSphere Application Server provides support for each of the

layers of the OSGi Architecture:

 The Modules layer

 The Life-cycle layer

 The Services layer

We discuss each of them in following sections.

26.1.1 OSGi application model

This section covers OSGi deployment, metadata, and the dependencies and capabilities of

OSGi through versioning.

OSGi bundles and bundle archives

The unit of deployment in OSGi is a bundle. A bundle is a standard JAR or WAR file with

additional metadata in the manifest file. Because the standard Java environment ignores

these additional properties, you can also use an OSGi bundle with classic Java applications.

There are several bundles and bundle archives within an OGSi application:

 Enterprise bundle archives

An

enterprise bundle archive file contains a set of OSGi bundles that are deployed as a

single OSGi application and isolated from other OSGi applications. Bundles that belong to

an OSGi application can reference other bundles that are in the shared bundle repository.

The external bundles referenced do not have to be included within the application as long

as the originating bundles import the required packages and the external bundles export

these packages as well.

 Composite bundles

A composite bundle actively groups shared bundles together into a

composite bundle

archive

file. This grouped bundle acts as a single bundle from the user perspective. It

provides one or more packages at

exact versions (not a version range) to an OSGi

application. When the OSGi framework resolves a package to a bundle within a composite

bundle archive, it has the affinity to resolve the remainder of the packages within the same

composite bundle archive.

Chapter 26. Working with OSGi applications 923

 Application bundles and shared bundles

Application bundles are instance-specific or

isolated, and each instance of an application

includes its own instance of the bundle. Shared bundles are

shared or not

instance-specific, and a single instance of a package or service from a shared bundle can

be used by many applications.

 Web application bundles

A

web application bundle is a bundle that contains a web application and that can be

deployed in an OSGi container.

 EJB bundles

An EJB bundle is a bundle that contains EJBs and that can be deployed in an OSGi

container. An EJB bundle is an OSGi bundle version of an EJB JAR file. It is a new feature

introduced in WebSphere Application Server V8.5.

For more information about OSGi bundles and bundle archives, refer to the following website:

http://www14.software.ibm.com/webapp/wsbroker/redirect?version=phil&product=was-nd

-dist&topic=ca_bundles

OSGi Bundle Manifest file

The metadata for an OSGi application is defined in manifest files. An OSGi bundle contains a

bundle manifest. A composite bundle archive contains a composite bundle manifest. An

enterprise bundle archive contains an application manifest. An enterprise bundle archive

asset contains a deployment manifest which is generated automatically when the enterprise

bundle archive file is imported as an asset.

In this section we focus on the OSGi bundle manifest located under META-INF/MANIFEST.MF.

For other manifest information, refer to the following website:

http://www14.software.ibm.com/webapp/wsbroker/redirect?version=phil&product=was-nd

-dist&topic=ca_manifest

We now check each element of the example manifest shown as Example 26-1.

Example 26-1 An example of bundle manifest file, META-INF/MANIFEST.MF

Manifest-Version: 1.0

Bundle-ManifestVersion: 2

Bundle-Name: MyLibrary bundle

Bundle-SymbolicName: com.sample.mylibrary

Bundle-Version: 42.0.0

Bundle-Activator: com.sample.mylibrary.Activator

Import-Package: org.osgi.framework;version=”[1.0.0,2.0.0)”

Export-Package:

com.sample.mylibrary.stringops;version=23.2.1,com.sample.mylibrary.integerops;ver

sion=5.0.0

Meta-Persistence: entities/persistence.xml,

lib/thirdPartyEntities.jar!/META-INF/persistence.xml

Web-ContextPath: /contextRoot

Export-EJB:

Bundle-Blueprint: /blueprint/*.xml