Welcome!

Java IoT Authors: Yeshim Deniz, Sanjeev Khurana, Liz McMillan, Matt Davis, Ed Featherston

Related Topics: Java IoT, Microservices Expo

Java IoT: Article

Component Development and Assembly Using OSGi Services

Using components to build software systems will provide many architectural advantages apart from promoting ease of reuse

This article introduces the concepts of Component Oriented Development and Assembly (CODA) using the OSGi Service platform with an example application. The article starts with an introduction to software components, elaborates with an example application, followed by an overview of the OSGi Service platform, and an implementation of the example application using this platform.

Introduction to Software Components
Components are parts that can be assembled to form a larger system. Electronic components such as ICs (Integrated Circuits) are assembled together to build an electronic system; similarly software components are assembled together to build a software system. Software systems have a static form as well as a dynamic runtime form. Software components can be assembled either in static form or dynamic form. In either case, the software component is an independent unit of development, deployment, and assembly. Using components to build software systems will provide many architectural advantages apart from promoting ease of reuse.

Age Calculation - An Example Application
Consider an application meant for calculating the age of people. Assume this application prompts the user to provide her personal details such as name and date of birth. Once the user provides the details, the application calculates the age of the person as of today and displays it with a personal greeting. Such an application can be built from the following software components:

  • UserProfile Component: Responsible for collecting the personal details of the user such as name and date of birth
  • Age Component: Responsible for calculating the age, given the date of birth
  • Greeting Component: Responsible for displaying the greeting message along with age of the person; needs to make use of the UserProfile component to obtain input from the user and Age component to calculate the age
  • AgeCalculationApp Component: Responsible for invoking the Greeting service provided by Greeting component

The components can be represented in a UML component diagram as shown in Figure 1. The dotted arrow lines in the diagram denote dependency.

Figure 1: Components in the Age Calculation application

Interfaces of Software Components
A software interface is a collection of software operations. Software components interact with one another by invoking the software operations. To facilitate structured interactions across components, each component exposes one or more software interfaces through which other components can interact. The exposed interfaces of a component are called as its "provided interfaces." Internals of the component implement the service contracts exposed by the provided interfaces.

Apart from providing services, a component needs to consume services provided by other components. The set of services that a component wants to consume is specified through "required interfaces". A component can work with any other component that provides the required interfaces. Hence there is no tight coupling between one component and another; the dependency of a component is only with interfaces and not with other components.

Interfaces in the Age Calculation Application
Let us identify the interfaces provided and required by each of the four components in the Age Calculation application.

Age Component
The Age component is responsible for calculating the age, given the date of birth. Hence it needs to provide a service for calculating the age. Let's expose this service through a provided interface IAgeCalculation. The Java code for this interface is given in Figure 2.

Figure 2: AgeCalculation Java interface code

In the IAgeCalculation interface definition, Calendar is a data type defined in java.util package to represent the date. IAge is a custom-defined data type to hold the age. The Java code for IAge is shown in Figure 3.

Figure 3: Java code for data type IAge

The Age Component can be represented in a UML component diagram as shown in Figure 4. The lollipop connector from the component denotes provided interface.

Figure 4: UML representation of Age component

UserProfile Component
The UserProfile component is responsible for collecting the personal information from end user and passing it back to the consuming component. Let us define an interface called as IUserProfileCollection to expose this service. The Java code for this interface is shown in Figure 5.

Figure 5: Java code for IUserProfileCollection interface

When the method collectUserProfile() is called, the component starts an interactive session with the end user to collect her personal information. During the user interaction session, the method isProfileCollected() will return false; after the user interaction session has finished and the user profile has been collected, this method will return true. At this time, the user profile is ready for pick-up by the consuming component and it can do so by invoking giveUserProfile() method.

giveUserProfile() method returns the user profile information through a custom defined data type IUserProfile. Java code for IUserProfile data type is given in Figure 6.

Figure 6: Java code for IUserProfile data type

The UserProfile component in a UML component diagram notation is shown in Figure 7.

Figure 7: UML representation of UserProfile component

Greeting Component
The Greeting component is responsible for displaying the greeting message along with the age. We'll expose this service through the IGreeting interface. The Java code for IGreeting interface is shown in Figure 8.

Figure 8: Java code for interface IGreeting

The Greeting component provides the IGreeting service, and it requires the IAgeCalculation and IUserProfileCollection services. The required and provided interfaces of the Greeting component can be represented using the UML component diagram as shown in Figure 9. The receptacle sockets in the component diagram denote required interfaces.

Figure 9: UML representation of Greeting component

AgeCalculationApp Component
The AgeCalculationApp component is responsible for invoking the IGreeting service of Greeting component. The AgeCalculationApp itself does not provide any service. The UML diagram for this component is shown in Figure 10.

Figure 10: UML representation of AgeCalculationApp

Application Assembly
Components are assembled together to build a software system. Components for an assembly should be chosen such a way that, amongst the chosen components the set of required interfaces is fulfilled by the set of provided interfaces. The four components of the example application can be assembled to result in Age Calculation application. UML component diagram denoting this assembly is shown in Figure 11. Connectors with a lollipop and a receptacle together show how two components assemble over a common interface (one component provides the interface and another component requires it).

Figure 11: UML representation of Age Calculation application assembly

Once an application is assembled, specific components from the assembly can be replaced with compatible newer components. Let us say we have two new components - GUIUserProfile and GUIGreeting, which have same interfaces as UserProfile and Greeting components, respectively. Then these new components can replace the old components to provide us with a GUI application. The application assembly would then look like Figure 12.

Figure 12: Age Calculation GUI Application Assembly

Introduction to the OSGi Service Platform
OSGi Service is a standards based software development platform. The platform standards are specified by the OSGi Alliance (http://www.osgi.org), formerly known as the Open Services Gateway initiative.  OSGi alliance is an industry backed nonprofit organization.

OSGi platform provides a modularity and component model on top of Java. Figure 13 illustrates how OSGi logically fits in a development / deployment stack.

Figure 13: OSGi From Development / Deployment Perspective

OSGi Framework
At the core of the OSGi platform is the OSGi framework defined by standards. OSGi framework is the runtime environment on which OSGi applications can be executed. OSGi framework specifies a common API using which application developers can develop OSGi applications. The OSGi framework specifications is used by OSGi framework developers also, who build implementations of the framework as per the specifications.

There are a number of framework implementations available from different developers. A few well known framework implementations are listed below:

The functionality of OSGi framework is divided into many layers. For our purposes, we shall focus on Modules Layer and Services Layer.  Figure 14 illustrates the layers we would like to focus.

The modules layer is the bottom most layer interacting with the runtime framework. The modules layer defines a modularity framework on top of standard Java so that modules expose and interact via well-defined APIs. Individual module is called as a "bundle" in OSGi. OSGi bundle is the atomic unit of deployment on an OSGi framework. An OSGi bundle is nothing but a Java Archive (JAR) File with some special manifest information that would be used by the OSGi framework when the bundle is deployed. Unlike a normal JAR file, which exposes all its code when it is deployed on a Java Virtual Machine (JVM), the bundle does not expose all the code contained within. Only code (Java packages) marked for explicit export is exposed outside the bundle.

Figure 14: OSGi Framework Functional Layers

Above the Module layer is the Services layer. An OSGi Service is defined by a Java interface. Any bundle can implement the service, and register the service with the OSGi Service Registry. OSGi Service Registry, defined as part of framework standards, supports a publish, subscribe, and look-up mechanism of exchanging services across components. A bundle can register the service that it has implemented with the OSGi Service Registry. A bundle requiring a service can query the OSGi Service Registry to look-up any registered service implementation. Instead of looking-up, a bundle can also subscribe to be notified on service registration / unregistration events. These mechanisms make the bundles that provide service and bundles that consume service unaware of each other, leading to independent development and deployment of these components. Once deployed, they can be  assembled dynamically using the OSGi Service Registry.

Implementing Age Calculation Using OSGi
The Age Calculation application has one bundle for each of the components. Each bundle has a Java package that is exposed for access from outside and an internal Java package. The exposed package defines the interfaces and the internal package contains implementation classes. The package diagram for all the bundles is shown in Figure 15.

Figure 15: Age Calculation Application bundles

The service provided by each bundle is exposed by using the OSGi Declarative Services framework. Using the same framework, each bundle also specifies the list of services it requires. The OSGi Declarative Services framework (also known as Service Component Runtime), will perform the work of registering the provided service with the OSGi Service Registry and obtaining the required service through look-up into OSGi Service Registry. Thus, the Declarative Services framework provides automatic assembly of deployed components.

As an example, let us consider the Greeting bundle. The Declarative Services specification of the components in this bundle is done through an XML file, which is given in Figure 16.

Figure 16: Greeting component Declarative Service Definition

The XML file contains following metadata about the Greeting component:

  • A component by name com.demo.greeting is defined
  • The component is implemented by the class com.demo.greeting.internal.Greeting
  • The component requires two interfaces - IuserProfileCollection and IAgeCalculation. These required interfaces should be dynamically wired to this component using setUserProfileCollection() and setAgeCalculation() methods on the component implementation class.
  • The component provides a service through the provided interface com.demo.greeting.IGreeting.

To understand how the Greeting component works, some portions of the implementation class is presented in Figure 17. The Greeting class has two field variables referring to the services required by this component. In the component Declarative Service metadata setter methods of these two variables are linked to the service reference (required interface). Hence when the Service Component Runtime (SCR) activates this component, it would call the setter methods to point these variables to objects which provide the service. For example, an instance of AgeCalculator object from Age component would be passed to ageCalculation_ member variable.

Figure 17: Implementation of Greeting component

The Greeting class's  implementation of greet() method obtains the user profile by invoking IUserProfileCollection service. From the obtained profile, date of birth is extracted and IAgeCalculation service is used to calculate the age. Finally the method displays the age along with a greeting to the user.

Output from the Example Application
The Age Calculation application, with console mode user interaction components, has the following output.

osgi> What is your first name?

Albert

What is your last name?

Einstein

What is your title (Mr./Ms./Mrs./Prof./Dr.)?

Mr.

What is your year of birth?

1879

What is your month of birth (1-12)?

03

What is your date of birth (1-31)?

14

Hello Mr. Albert Einstein, you are 132 years, 10 months, and 3 days old.

If we replace the Greeting and UserProfile components in the application assembly with GUIGreeting and GUIUserProfile components, the application output is as below:

The source code of the application can be downloaded as a zip file containing an Eclipse workspace folder. To open the source code and run the application simply unzip the folder and switch the Eclipse workspace to point to the unzipped folder. Choose the appropriate components in the Run Configuration to run either console version or the GUI version of the assembly. For example, for the GUI version, the following run configuration will be applicable:

More Stories By Piram Manickam

Piram Manickam works at Infosys Limited. He would like to acknowledge and thank Sangeetha S, a beloved colleague and friend, for her invaluable contributions in this work.

More Stories By Subrahmanya SV

Subrahmanya SV works at Infosys Limited. He would like to acknowledge and thank Sangeetha S, a beloved colleague and friend, for her invaluable contributions in this work.

Comments (1) View Comments

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


Most Recent Comments
newuniverse 01/31/12 03:10:00 AM EST

Hi,
This is a very simple and descriptive example. Good job.

@ThingsExpo Stories
SYS-CON Events announced today that Linux Academy, the foremost online Linux and cloud training platform and community, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Linux Academy was founded on the belief that providing high-quality, in-depth training should be available at an affordable price. Industry leaders in quality training, provided services, and student certification passes, its goal is to c...
SYS-CON Events announced today that Interoute, owner-operator of one of Europe's largest networks and a global cloud services platform, has been named “Bronze Sponsor” of SYS-CON's 20th Cloud Expo, which will take place on June 6-8, 2017 at the Javits Center in New York, New York. Interoute is the owner-operator of one of Europe's largest networks and a global cloud services platform which encompasses 12 data centers, 14 virtual data centers and 31 colocation centers, with connections to 195 add...
What sort of WebRTC based applications can we expect to see over the next year and beyond? One way to predict development trends is to see what sorts of applications startups are building. In his session at @ThingsExpo, Arin Sime, founder of WebRTC.ventures, will discuss the current and likely future trends in WebRTC application development based on real requests for custom applications from real customers, as well as other public sources of information,
SYS-CON Events announced today that Telecom Reseller has been named “Media Sponsor” of SYS-CON's 20th International Cloud Expo, which will take place on June 6–8, 2017, at the Javits Center in New York City, NY. Telecom Reseller reports on Unified Communications, UCaaS, BPaaS for enterprise and SMBs. They report extensively on both customer premises based solutions such as IP-PBX as well as cloud based and hosted platforms.
SYS-CON Events announced today that Loom Systems will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Founded in 2015, Loom Systems delivers an advanced AI solution to predict and prevent problems in the digital business. Loom stands alone in the industry as an AI analysis platform requiring no prior math knowledge from operators, leveraging the existing staff to succeed in the digital era. With offices in S...
Keeping pace with advancements in software delivery processes and tooling is taxing even for the most proficient organizations. Point tools, platforms, open source and the increasing adoption of private and public cloud services requires strong engineering rigor - all in the face of developer demands to use the tools of choice. As Agile has settled in as a mainstream practice, now DevOps has emerged as the next wave to improve software delivery speed and output. To make DevOps work, organization...
SYS-CON Events announced today that T-Mobile will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. As America's Un-carrier, T-Mobile US, Inc., is redefining the way consumers and businesses buy wireless services through leading product and service innovation. The Company's advanced nationwide 4G LTE network delivers outstanding wireless experiences to 67.4 million customers who are unwilling to compromise on ...
SYS-CON Events announced today that Cloudistics, an on-premises cloud computing company, has been named “Bronze Sponsor” of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Cloudistics delivers a complete public cloud experience with composable on-premises infrastructures to medium and large enterprises. Its software-defined technology natively converges network, storage, compute, virtualization, and management into a ...
SYS-CON Events announced today that CA Technologies has been named “Platinum Sponsor” of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY, and the 21st International Cloud Expo®, which will take place October 31-November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. CA Technologies helps customers succeed in a future where every business – from apparel to energy – is being rewritten by software. From ...
SYS-CON Events announced today that Infranics will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Since 2000, Infranics has developed SysMaster Suite, which is required for the stable and efficient management of ICT infrastructure. The ICT management solution developed and provided by Infranics continues to add intelligence to the ICT infrastructure through the IMC (Infra Management Cycle) based on mathemat...
Now that the world has connected “things,” we need to build these devices as truly intelligent in order to create instantaneous and precise results. This means you have to do as much of the processing at the point of entry as you can: at the edge. The killer use cases for IoT are becoming manifest through AI engines on edge devices. An autonomous car has this dual edge/cloud analytics model, producing precise, real-time results. In his session at @ThingsExpo, John Crupi, Vice President and Eng...
In the enterprise today, connected IoT devices are everywhere – both inside and outside corporate environments. The need to identify, manage, control and secure a quickly growing web of connections and outside devices is making the already challenging task of security even more important, and onerous. In his session at @ThingsExpo, Rich Boyer, CISO and Chief Architect for Security at NTT i3, will discuss new ways of thinking and the approaches needed to address the emerging challenges of securit...
The taxi industry never saw Uber coming. Startups are a threat to incumbents like never before, and a major enabler for startups is that they are instantly “cloud ready.” If innovation moves at the pace of IT, then your company is in trouble. Why? Because your data center will not keep up with frenetic pace AWS, Microsoft and Google are rolling out new capabilities In his session at 20th Cloud Expo, Don Browning, VP of Cloud Architecture at Turner, will posit that disruption is inevitable for c...
There are 66 million network cameras capturing terabytes of data. How did factories in Japan improve physical security at the facilities and improve employee productivity? Edge Computing reduces possible kilobytes of data collected per second to only a few kilobytes of data transmitted to the public cloud every day. Data is aggregated and analyzed close to sensors so only intelligent results need to be transmitted to the cloud. Non-essential data is recycled to optimize storage.
As businesses adopt functionalities in cloud computing, it’s imperative that IT operations consistently ensure cloud systems work correctly – all of the time, and to their best capabilities. In his session at @BigDataExpo, Bernd Harzog, CEO and founder of OpsDataStore, will present an industry answer to the common question, “Are you running IT operations as efficiently and as cost effectively as you need to?” He will expound on the industry issues he frequently came up against as an analyst, and...
In his General Session at 16th Cloud Expo, David Shacochis, host of The Hybrid IT Files podcast and Vice President at CenturyLink, investigated three key trends of the “gigabit economy" though the story of a Fortune 500 communications company in transformation. Narrating how multi-modal hybrid IT, service automation, and agile delivery all intersect, he will cover the role of storytelling and empathy in achieving strategic alignment between the enterprise and its information technology.
"I think that everyone recognizes that for IoT to really realize its full potential and value that it is about creating ecosystems and marketplaces and that no single vendor is able to support what is required," explained Esmeralda Swartz, VP, Marketing Enterprise and Cloud at Ericsson, in this SYS-CON.tv interview at @ThingsExpo, held June 7-9, 2016, at the Javits Center in New York City, NY.
Microservices are a very exciting architectural approach that many organizations are looking to as a way to accelerate innovation. Microservices promise to allow teams to move away from monolithic "ball of mud" systems, but the reality is that, in the vast majority of organizations, different projects and technologies will continue to be developed at different speeds. How to handle the dependencies between these disparate systems with different iteration cycles? Consider the "canoncial problem" ...
SYS-CON Events announced today that HTBase will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. HTBase (Gartner 2016 Cool Vendor) delivers a Composable IT infrastructure solution architected for agility and increased efficiency. It turns compute, storage, and fabric into fluid pools of resources that are easily composed and re-composed to meet each application’s needs. With HTBase, companies can quickly prov...
SYS-CON Events announced today that SoftLayer, an IBM Company, has been named “Gold Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2016, at the Javits Center in New York, New York. SoftLayer, an IBM Company, provides cloud infrastructure as a service from a growing number of data centers and network points of presence around the world. SoftLayer’s customers range from Web startups to global enterprises.