OSGi
From Wikipedia, the free encyclopedia
The OSGi Alliance (formerly known as the Open Services Gateway initiative, now an obsolete name) is an open standards organization founded in March 1999. The Alliance and its members have specified a Java-based service platform that can be remotely managed. The core part of the specifications is a framework that defines an application life cycle management model, a service registry, an Execution environment and Modules. Based on this framework, a large number of OSGi Layers, APIs, and Services have been defined.
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[edit] OSGi Framework Scope
The Framework implements a complete and dynamic component model, something that is missing in standalone Java/VM environments. Applications or components (coming in the form of bundles for deployment) can be remotely installed, started, stopped, updated and uninstalled without requiring a reboot; management of Java packages/classes is specified in great detail. Life cycle management is done via APIs which 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.
The original focus was on service gateways but the applicability turned out to be much wider. The OSGi specifications are now used in applications ranging from mobile phones to the open source Eclipse IDE. Other application areas include cars, industrial automation, building automation, PDAs, grid computing, entertainment (e.g. iPronto), fleet management and application servers.
[edit] Specification Process
The OSGi specification is developed by the members in an open process and made available to the public free of charge under the OSGi Specification License [1]. The OSGi Alliance has a compliance program that is open to members only. As of September 2008, the list of certified OSGi implementations contains five entries.
[edit] Architecture
Frameworks that implement the OSGi standard provide an environment for the modularization of applications into smaller bundles. Each bundle is a tightly-coupled, dynamically loadable collection of classes, jars, and configuration files that explicitly declare their external dependencies (if any).
The framework is conceptually divided into the following areas:
[edit] Organization
The OSGi Alliance was founded by Ericsson, IBM, Oracle, Sun Microsystems and others in March 1999 (before incorporating as a nonprofit corporation it was called the Connected Alliance).
Among its members are (as of May 2007) more than 35 companies from quite different business areas, for example IONA Technologies, Ericsson, Deutsche Telekom, IBM, Makewave (formerly Gatespace Telematics), Motorola, Nokia, NTT, Oracle, ProSyst, Red Hat, Samsung Electronics, Siemens, SpringSource, and Telefonica.
The Alliance has a Board of Directors which provides the organization's overall governance. OSGi Officers have various roles and responsibilities in supporting the Alliance. Technical work is conducted within Expert Groups (EGs) chartered by the Board of Directors, and non-technical work is conducted in various Working Groups and Committees. The technical work conducted within Expert Groups include developing specifications, reference implementations, and compliance tests. These Expert Groups, working together, have produced four major releases of the OSGi specifications (as of 2007).
There are dedicated Expert Groups for the Enterprise, Mobile, Vehicle and the Core Platform areas. The Enterprise Expert Group (EEG) is the newest EG and is addressing Enterprise / Server-side applications. In November 2007 the Residential Expert Group (REG) started to work on specifications to remotely manage residential/home-gateways.
[edit] Community
In October 2003, Nokia, Motorola, IBM, ProSyst and other OSGi members formed a Mobile Expert Group (MEG) that will specify a MIDP-based service platform for the next generation of smart mobile phones, addressing some of the needs that CLDC cannot manage - other than CDC. MEG became part of OSGi as with R4.
Also in 2003 Eclipse selected OSGi as the underlying runtime for the plug-in architecture used for the Eclipse Rich Client Platform and the IDE platform. Eclipse itself includes sophisticated tooling for developing OSGi bundles and there are a number of other Eclipse plug-ins aimed at supporting OSGi behaviour (e.g. both ProSyst and Knopflerfish have Eclipse plug-ins available specifically for OSGi developers).
There is a vibrant free software community revolving around the OSGi. Some widely-used open source implementations are Equinox OSGi, Apache Felix [1], Knopflerfish OSGi project as well as the mBedded Server Equinox Edition. Regarding tooling, build system support and testing, the OPS4J Pax projects provide a lot of useful components and expertise.
[edit] Specification Versions
[edit] New in OSGi Release 4
The new features of OSGi R4 in brief are as follows :
