Welcome!

SOA & WOA Authors: Sandi Mappic, Ivan Antsipau, Carmen Gonzalez, Paul Speciale, Lori MacVittie

Related Topics: SOA & WOA, Java, XML, AJAX & REA

SOA & WOA: Article

The OSGi puzzle

Let's discover the OSGi architecture.

OSGi became very popular thanks to its modularity approach and its ability to enforce logical boundaries between modules. When we discover it the first time, the question is where to begin to understand how it works?

To understand OSGi concepts we will try to follow the puzzle approach. The idea is to begin with the trivial part of this technology, and search for other parts related to the found ones. And to assemble the puzzle we will be assisted by JArchitect that will be helpful to detect OSGi internal design.

To be more concrete we analyze with JArchitect an application using OSGi technology, it concern the famous eclipse IDE which use the OSGi container equinox.



Let's begin with the typical OSGi definition:

OSGi reduces complexity by providing a modular architecture for today's large-scale distributed systems as well as small, embedded applications. Building systems from in-house and off-the-shelf modules significantly reduces complexity and thus development and maintenance expenses. The OSGi programming model realizes the promise of component-based systems.

The trivial part of OSGi is modularity, let's discover what's the OSGi modules

OSGI modules are called Bundles and every application therefore consist of at least one bundle.

These bundles are executed inside a container, and as each modular approach where a container manage the modules, the question is which contract must implement every module to be intergated into the container?

Let's take as example the bundle org.eclipse.equinox.jsp.jasper and search for all its implemented interfaces, for that we can execute the following CQLinq request:

from t in Types where t.ParentProject.Name=="org.eclipse.equinox.jsp.jasper_1.0.300.v20110502" let interfaces=t.InterfacesImplemented from i in interfaces select i



The BundleActivator interface from OSGi package is implemented, this interface contains two methods start and stop useful to customizes the starting and stopping of the bundle.

Manifest-Version: 1.0

Bundle-Localization: plugin

Bundle-RequiredExecutionEnvironment: CDC-1.0/Foundation-1.0,J2SE-1.3

Bundle-SymbolicName: org.eclipse.equinox.jsp.jasper

Eclipse-LazyStart: true

Eclipse-SourceReferences: scm:cvs:pserver:dev.eclipse.org:/cvsroot/rt:

 org.eclipse.equinox/server-side/bundles/org.eclipse.equinox.jsp.jaspe

 r;tag=v20110502

Bundle-Activator: org.eclipse.equinox.internal.jsp.jasper.Activator


Another specificity of a bundle is its manifest file, here's a part from the org.eclipse.equinox.jsp.jasper manifest file:

Manifest-Version: 1.0

Bundle-Localization: plugin

Bundle-RequiredExecutionEnvironment: CDC-1.0/Foundation-1.0,J2SE-1.3

Bundle-SymbolicName: org.eclipse.equinox.jsp.jasper

Eclipse-LazyStart: true

Eclipse-SourceReferences: scm:cvs:pserver:dev.eclipse.org:/cvsroot/rt:

 org.eclipse.equinox/server-side/bundles/org.eclipse.equinox.jsp.jaspe

 r;tag=v20110502

Bundle-Activator: org.eclipse.equinox.internal.jsp.jasper.Activator

As we can observe this manifest contains some meta informations needed by the container, like specifying the bundle activator class which implements the BundleActivator interface.

The bundle represent our first piece of the puzzle,and here's a simplified representation of a bundle:



And just to have an idea of all bundles used by eclipse, let's search for all classes implementing BundleActivator interface.

from t in Types where t.Implement ("org.osgi.framework.BundleActivator") select new { t, t.NbBCInstructions }



Who manage the bundle and invoke BundleActivator methods?

To discover that let's search for methods invoking directly or indirectly BundleActivator.start

from m in Methods let depth0 = m.DepthOfIsUsing ("org.eclipse.osgi.framework.internal.core.BundleContextImpl.startActivator(BundleActivator)") where depth0 >= 0 orderby depth0 select new { m, depth0 }



The bundle is activated by the OSGi framework when it's launched. the framework class is started by the equinox container. And to understand better what happen when the container start, here are some actions executed when the container is launched:



When the container is launched, it initialize the OSGi framework, the framework gets all installed bundles, and for each one it create an instance of BundleHost class, and store into a repository the found bundle.

The BundleHost class implement the Bundle interface, which contains methods like start,stop,uninstall and update, these methods are needed to manage the bundle life cycle.

So our second puzzle piece is The OSGi container, it's launched by the Equinoxlauncher, which initialise the framework. The framework class is responsible of loading bundles and activate them.

After discovering some basic concepts about bundle and container, let's go deep inside bundles and discover how they works internally.

Let's take as example the org.eclipse.equinox.http.servlet bundle and search for methods invoked by the start method of its Activator class.



This bundle create a service and register it into the container. A service in OSGi is defined by a standard Java class or interface. Typically a Java interface is used to define the service interface. The service is the preferred method bundles should use to communicate between each other.

Here are some useful scenarios of using services:

  • Export functionality from a bundle to other bundles.
  • Import functionality from other bundles.
  • Register listeners for events from other bundles.


Another remark from the previous dependecy graph is that a service factory is used to create the service instance.

Our third piece of the puzzle is the OSGi services layer, each bundle can use or declare some services , what enforce the component design approach, here's the new representation of the OSGi bundle.



If The bundle use services to communicate with other bundles, how it communicate with other jars?

If we develop a bundle and try to use a class from another jar, we can be surprised that it will not works as expected, the reason is that the ClassLoader is hooked by the OSGi container, to check that let's search which method invoke java.lang.Thread.setContextClassLoader.

from m in Methods where m.IsUsing ("java.lang.Thread.setContextClassLoader(ClassLoader)") select new { m, m.NbBCInstructions }



Many methods invoke it including the EquinoxLauncher. so every time the bundle try to create a class instance, the OSGi container will check if the code is permited to did this action or not, and here come the role of imported and exported package in the manifest file.

Export-Package: org.eclipse.equinox.http.servlet;version="1.1.0"



Import-Package: javax.servlet;version="2.3",javax.servlet.http;version

 ="2.3",org.osgi.framework;version="1.3.0",org.osgi.service.http;versi

 on="[1.2,1.3)" 



The bundle declare explicitly exported and imported package, and to check that , let's search for packages used by org.eclipse.equinox.http.servlet bundle and verify if it use only package imported.

from n in Packages where n.IsUsedBy ("org.eclipse.equinox.http.servlet_1.1.200.v20110502") select new { n, n.NbBCInstructions }



As we can observe all packages used are specified in the manifest file , in the import package section.
The exported package however represent the package that can be used from other bundles. it's represented by the ExportedPackage interface, and we can search for the container classes using this interface.

from t in Types where t.IsUsing ("org.osgi.service.packageadmin.ExportedPackage") select new { t, t.NbBCInstructions }



What interesting with this new capability, is that the bundle will have a well defined boundary, and what it use and what it expose as services is very well specified.

We can enforce the check of using imported packages by using other tools, for example with CQLinq we can write some rules warning each time a project use packages other than specified ones, but it's better to have this check in the execution environement, so the developer can't break this rules.

This capability to treat imported and exported packages is managed by the OSGi modules layer and it was our fourth piece of the puzzle.

Let's come back to the OSGi container and discover which services it provides?

Container services

As we discoverd before the container is launched by the EquinoxLauncher class and the framework class initialise and launch the bundles, to detect which services re provided let's search for all classes used in the framework initalisation method.
from t in Types where t.IsUsedBy ("org.eclipse.osgi.framework.internal.core.Framework.initialize(FrameworkAdaptor)") select new { t, t.NbBCInstructions }

Some classes are already discovered before like BundleRepository,BundleHost,PackageAdminImpl and ServiceRegistry.

What about the other classes:

  • StartLevelManager: Each OSGi Bundle is associated with a start level that enable the server to control the relative starting and stopping order of bundles. Only bundles that have a start level less or equal to the active start level of the server framework must be active. Usually, a bundle with a smaller start level tend to be started earlier.
  • SecurityAdmin: The security layer handles the security aspects by limiting bundle functionality to pre-defined capabilities.
  • EventManager: The Event Admin service provides a publish-subscribe model for handling events. It is realized according to the OSGi Event Admin Service Specification. The Event Admin service dispatches events between Event Publishers and Event Subscribers (Event Handlers) by interposing an event channel. Publishers post events to the channel and the event channel defines which handlers needs to be notified. Thus publishers and handlers have no direct knowledge of each other, which simplifies event management.


The OSGi whole picture
Let's assemble all puzzle pieces described before , and we will have the following OSGi picture:


This architecture has the following interesting benefits:

  • Simple.
  • Reduced Complexity.
  • Easy Deployment.
  • Secure.


What makes it very attractif and Worth a Detour, and you will not waste your time if you study it in depth.

More Stories By Lahlali Issam

Lahlali Issam Lead Developer at JavaDepend, a tool to manage and understand complex Java code. With JavaDepend, software quality can be measured using Code Metrics, visualized using Graphs and Treemaps, and queried using CQL language, a SQL like to query the code base.

@ThingsExpo Stories
The Internet of Things will greatly expand the opportunities for data collection and new business models driven off of that data. In her session at Internet of @ThingsExpo, Esmeralda Swartz, CMO of MetraTech, will discuss how for this to be effective you not only need to have infrastructure and operational models capable of utilizing this new phenomenon, but increasingly service providers will need to convince a skeptical public to participate. Get ready to show them the money! Speaker Bio: Esmeralda Swartz, CMO of MetraTech, has spent 16 years as a marketing, product management, and busin...
Samsung VP Jacopo Lenzi, who headed the company's recent SmartThings acquisition under the auspices of Samsung's Open Innovaction Center (OIC), answered a few questions we had about the deal. This interview was in conjunction with our interview with SmartThings CEO Alex Hawkinson. IoT Journal: SmartThings was developed in an open, standards-agnostic platform, and will now be part of Samsung's Open Innovation Center. Can you elaborate on your commitment to keep the platform open? Jacopo Lenzi: Samsung recognizes that true, accelerated innovation cannot be driven from one source, but requires a...
SYS-CON Events announced today that Red Hat, the world's leading provider of open source solutions, will exhibit at Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Red Hat is the world's leading provider of open source software solutions, using a community-powered approach to reliable and high-performing cloud, Linux, middleware, storage and virtualization technologies. Red Hat also offers award-winning support, training, and consulting services. As the connective hub in a global network of enterprises, partners, a...
P2P RTC will impact the landscape of communications, shifting from traditional telephony style communications models to OTT (Over-The-Top) cloud assisted & PaaS (Platform as a Service) communication services. The P2P shift will impact many areas of our lives, from mobile communication, human interactive web services, RTC and telephony infrastructure, user federation, security and privacy implications, business costs, and scalability. In his session at Internet of @ThingsExpo, Robin Raymond, Chief Architect at Hookflash Inc., will walk through the shifting landscape of traditional telephone a...
SYS-CON Events announced today that Matrix.org has been named “Silver Sponsor” of Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Matrix is an ambitious new open standard for open, distributed, real-time communication over IP. It defines a new approach for interoperable Instant Messaging and VoIP based on pragmatic HTTP APIs and WebRTC, and provides open source reference implementations to showcase and bootstrap the new standard. Our focus is on simplicity, security, and supporting the fullest feature set.
BSQUARE is a global leader of embedded software solutions. We enable smart connected systems at the device level and beyond that millions use every day and provide actionable data solutions for the growing Internet of Things (IoT) market. We empower our world-class customers with our products, services and solutions to achieve innovation and success. For more information, visit www.bsquare.com.
How do APIs and IoT relate? The answer is not as simple as merely adding an API on top of a dumb device, but rather about understanding the architectural patterns for implementing an IoT fabric. There are typically two or three trends: Exposing the device to a management framework Exposing that management framework to a business centric logic • Exposing that business layer and data to end users. This last trend is the IoT stack, which involves a new shift in the separation of what stuff happens, where data lives and where the interface lies. For instance, it’s a mix of architectural style...
SYS-CON Events announced today that SOA Software, an API management leader, will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. SOA Software is a leading provider of API Management and SOA Governance products that equip business to deliver APIs and SOA together to drive their company to meet its business strategy quickly and effectively. SOA Software’s technology helps businesses to accelerate their digital channels with APIs, drive partner adoption, monetize their assets, and achieve a...
From a software development perspective IoT is about programming "things," about connecting them with each other or integrating them with existing applications. In his session at @ThingsExpo, Yakov Fain, co-founder of Farata Systems and SuranceBay, will show you how small IoT-enabled devices from multiple manufacturers can be integrated into the workflow of an enterprise application. This is a practical demo of building a framework and components in HTML/Java/Mobile technologies to serve as a platform that can integrate new devices as they become available on the market.
SYS-CON Events announced today that Utimaco will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Utimaco is a leading manufacturer of hardware based security solutions that provide the root of trust to keep cryptographic keys safe, secure critical digital infrastructures and protect high value data assets. Only Utimaco delivers a general-purpose hardware security module (HSM) as a customizable platform to easily integrate into existing software solutions, embed business logic and build s...
Connected devices are changing the way we go about our everyday life, from wearables to driverless cars, to smart grids and entire industries revolutionizing business opportunities through smart objects, capable of two-way communication. But what happens when objects are given an IP-address, and we rely on that connection, sometimes with our lives? How do we secure those vast data infrastructures and safe-keep the privacy of sensitive information? This session will outline how each and every connected device can uphold a core root of trust via a unique cryptographic signature – a “bir...
Internet of @ThingsExpo Silicon Valley announced on Thursday its first 12 all-star speakers and sessions for its upcoming event, which will take place November 4-6, 2014, at the Santa Clara Convention Center in California. @ThingsExpo, the first and largest IoT event in the world, debuted at the Javits Center in New York City in June 10-12, 2014 with over 6,000 delegates attending the conference. Among the first 12 announced world class speakers, IBM will present two highly popular IoT sessions, which will take place November 4-6, 2014 at the Santa Clara Convention Center in Santa Clara, Calif...
Almost everyone sees the potential of Internet of Things but how can businesses truly unlock that potential. The key will be in the ability to discover business insight in the midst of an ocean of Big Data generated from billions of embedded devices via Systems of Discover. Businesses will also need to ensure that they can sustain that insight by leveraging the cloud for global reach, scale and elasticity.
WebRTC defines no default signaling protocol, causing fragmentation between WebRTC silos. SIP and XMPP provide possibilities, but come with considerable complexity and are not designed for use in a web environment. In his session at Internet of @ThingsExpo, Matthew Hodgson, technical co-founder of the Matrix.org, will discuss how Matrix is a new non-profit Open Source Project that defines both a new HTTP-based standard for VoIP & IM signaling and provides reference implementations.

SUNNYVALE, Calif., Oct. 20, 2014 /PRNewswire/ -- Spansion Inc. (NYSE: CODE), a global leader in embedded systems, today added 96 new products to the Spansion® FM4 Family of flexible microcontrollers (MCUs). Based on the ARM® Cortex®-M4F core, the new MCUs boast a 200 MHz operating frequency and support a diverse set of on-chip peripherals for enhanced human machine interfaces (HMIs) and machine-to-machine (M2M) communications. The rich set of periphera...

SYS-CON Events announced today that Aria Systems, the recurring revenue expert, has been named "Bronze Sponsor" of SYS-CON's 15th International Cloud Expo®, which will take place on November 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Aria Systems helps leading businesses connect their customers with the products and services they love. Industry leaders like Pitney Bowes, Experian, AAA NCNU, VMware, HootSuite and many others choose Aria to power their recurring revenue business and deliver exceptional experiences to their customers.
The Internet of Things (IoT) is going to require a new way of thinking and of developing software for speed, security and innovation. This requires IT leaders to balance business as usual while anticipating for the next market and technology trends. Cloud provides the right IT asset portfolio to help today’s IT leaders manage the old and prepare for the new. Today the cloud conversation is evolving from private and public to hybrid. This session will provide use cases and insights to reinforce the value of the network in helping organizations to maximize their company’s cloud experience.
The Internet of Things (IoT) is making everything it touches smarter – smart devices, smart cars and smart cities. And lucky us, we’re just beginning to reap the benefits as we work toward a networked society. However, this technology-driven innovation is impacting more than just individuals. The IoT has an environmental impact as well, which brings us to the theme of this month’s #IoTuesday Twitter chat. The ability to remove inefficiencies through connected objects is driving change throughout every sector, including waste management. BigBelly Solar, located just outside of Boston, is trans...
SYS-CON Events announced today that Matrix.org has been named “Silver Sponsor” of Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Matrix is an ambitious new open standard for open, distributed, real-time communication over IP. It defines a new approach for interoperable Instant Messaging and VoIP based on pragmatic HTTP APIs and WebRTC, and provides open source reference implementations to showcase and bootstrap the new standard. Our focus is on simplicity, security, and supporting the fullest feature set.
Predicted by Gartner to add $1.9 trillion to the global economy by 2020, the Internet of Everything (IoE) is based on the idea that devices, systems and services will connect in simple, transparent ways, enabling seamless interactions among devices across brands and sectors. As this vision unfolds, it is clear that no single company can accomplish the level of interoperability required to support the horizontal aspects of the IoE. The AllSeen Alliance, announced in December 2013, was formed with the goal to advance IoE adoption and innovation in the connected home, healthcare, education, aut...