|By Piram Manickam, Subrahmanya SV||
|April 10, 2012 01:30 PM EDT||
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.
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
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
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
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
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
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:
- Apache Felix (http://felix.apache.org)
- Eclipse Equinox (http://www.eclipse.org/equinox)
- Knoplerfish (http://www.knoplerfish.org)
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?
What is your last name?
What is your title (Mr./Ms./Mrs./Prof./Dr.)?
What is your year of birth?
What is your month of birth (1-12)?
What is your date of birth (1-31)?
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:
|newuniverse 01/31/12 03:10:00 AM EST|
In a previous article, I demonstrated how to effectively and efficiently install the Dynatrace Application Monitoring solution using Ansible. In this post, I am going to explain how to achieve the same results using Chef with our official dynatrace cookbook available on GitHub and on the Chef Supermarket. In the following hands-on tutorial, we’ll also apply what we see as good practice on working with and extending our deployment automation blueprints to suit your needs.
Feb. 11, 2016 05:00 AM EST
Let’s face it, embracing new storage technologies, capabilities and upgrading to new hardware often adds complexity and increases costs. In his session at 18th Cloud Expo, Seth Oxenhorn, Vice President of Business Development & Alliances at FalconStor, will discuss how a truly heterogeneous software-defined storage approach can add value to legacy platforms and heterogeneous environments. The result reduces complexity, significantly lowers cost, and provides IT organizations with improved effi...
Feb. 11, 2016 02:30 AM EST Reads: 252
How is your DevOps transformation coming along? How do you measure Agility? Reliability? Efficiency? Quality? Success?! How do you optimize your processes? This morning on #c9d9 we talked about some of the metrics that matter for the different stakeholders throughout the software delivery pipeline. Our panelists shared their best practices.
Feb. 11, 2016 02:00 AM EST Reads: 107
The cloud promises new levels of agility and cost-savings for Big Data, data warehousing and analytics. But it’s challenging to understand all the options – from IaaS and PaaS to newer services like HaaS (Hadoop as a Service) and BDaaS (Big Data as a Service). In her session at @BigDataExpo at @ThingsExpo, Hannah Smalltree, a director at Cazena, will provide an educational overview of emerging “as-a-service” options for Big Data in the cloud. This is critical background for IT and data profes...
Feb. 11, 2016 01:15 AM EST Reads: 209
SYS-CON Events announced today that Men & Mice, the leading global provider of DNS, DHCP and IP address management overlay solutions, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. The Men & Mice Suite overlay solution is already known for its powerful application in heterogeneous operating environments, enabling enterprises to scale without fuss. Building on a solid range of diverse platform support,...
Feb. 11, 2016 01:00 AM EST Reads: 223
Father business cycles and digital consumers are forcing enterprises to respond faster to customer needs and competitive demands. Successful integration of DevOps and Agile development will be key for business success in today’s digital economy. In his session at DevOps Summit, Pradeep Prabhu, Co-Founder & CEO of Cloudmunch, covered the critical practices that enterprises should consider to seamlessly integrate Agile and DevOps processes, barriers to implementing this in the enterprise, and pr...
Feb. 11, 2016 01:00 AM EST Reads: 406
If we look at slow, traditional IT and jump to the conclusion that just because we found its issues intractable before, that necessarily means we will again, then it’s time for a rethink. As a matter of fact, the world of IT has changed over the last ten years or so. We’ve been experiencing unprecedented innovation across the board – innovation in technology as well as in how people organize and accomplish tasks. Let’s take a look at three differences between today’s modern, digital context...
Feb. 11, 2016 12:45 AM EST Reads: 214
Sensors and effectors of IoT are solving problems in new ways, but small businesses have been slow to join the quantified world. They’ll need information from IoT using applications as varied as the businesses themselves. In his session at @ThingsExpo, Roger Meike, Distinguished Engineer, Director of Technology Innovation at Intuit, showed how IoT manufacturers can use open standards, public APIs and custom apps to enable the Quantified Small Business. He used a Raspberry Pi to connect sensors...
Feb. 11, 2016 12:45 AM EST Reads: 162
The principles behind DevOps are not new - for decades people have been automating system administration and decreasing the time to deploy apps and perform other management tasks. However, only recently did we see the tools and the will necessary to share the benefits and power of automation with a wider circle of people. In his session at DevOps Summit, Bernard Sanders, Chief Technology Officer at CloudBolt Software, explored the latest tools including Puppet, Chef, Docker, and CMPs needed to...
Feb. 11, 2016 12:30 AM EST Reads: 329
One of the bewildering things about DevOps is integrating the massive toolchain including the dozens of new tools that seem to crop up every year. Part of DevOps is Continuous Delivery and having a complex toolchain can add additional integration and setup to your developer environment. In his session at @DevOpsSummit at 18th Cloud Expo, Miko Matsumura, Chief Marketing Officer of Gradle Inc., will discuss which tools to use in a developer stack, how to provision the toolchain to minimize onboa...
Feb. 10, 2016 11:45 PM EST Reads: 111
Data-as-a-Service is the complete package for the transformation of raw data into meaningful data assets and the delivery of those data assets. In her session at 18th Cloud Expo, Lakshmi Randall, an industry expert, analyst and strategist, will address: What is DaaS (Data-as-a-Service)? Challenges addressed by DaaS Vendors that are enabling DaaS Architecture options for DaaS
Feb. 10, 2016 11:45 PM EST Reads: 352
SYS-CON Events announced today that Avere Systems, a leading provider of enterprise storage for the hybrid cloud, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Avere delivers a more modern architectural approach to storage that doesn’t require the overprovisioning of storage capacity to achieve performance, overspending on expensive storage media for inactive data or the overbuilding of data centers ...
Feb. 10, 2016 09:00 PM EST
SYS-CON Events announced today that Catchpoint Systems, Inc., a provider of innovative web and infrastructure monitoring solutions, has been named “Silver Sponsor” of SYS-CON's DevOps Summit at 18th Cloud Expo New York, which will take place June 7-9, 2016, at the Javits Center in New York City, NY. Catchpoint is a leading Digital Performance Analytics company that provides unparalleled insight into customer-critical services to help consistently deliver an amazing customer experience. Designed...
Feb. 10, 2016 04:00 PM EST Reads: 379
With the proliferation of both SQL and NoSQL databases, organizations can now target specific fit-for-purpose database tools for their different application needs regarding scalability, ease of use, ACID support, etc. Platform as a Service offerings make this even easier now, enabling developers to roll out their own database infrastructure in minutes with minimal management overhead. However, this same amount of flexibility also comes with the challenges of picking the right tool, on the right ...
Feb. 10, 2016 04:00 PM EST Reads: 163
SYS-CON Events announced today that Alert Logic, Inc., the leading provider of Security-as-a-Service solutions for the cloud, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Alert Logic, Inc., provides Security-as-a-Service for on-premises, cloud, and hybrid infrastructures, delivering deep security insight and continuous protection for customers at a lower cost than traditional security solutions. Ful...
Feb. 10, 2016 02:30 PM EST Reads: 430
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 18th Cloud Expo, which will take place on June 7-9, 2015 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 ad...
Feb. 10, 2016 02:30 PM EST Reads: 399
The (re?)emergence of Microservices was especially prominent in this week’s news. What are they good for? do they make sense for your application? should you take the plunge? and what do Microservices mean for your DevOps and Continuous Delivery efforts? Continue reading for more on Microservices, containers, DevOps culture, and more top news from the past week. As always, stay tuned to all the news coming from@ElectricCloud on DevOps and Continuous Delivery throughout the week and retweet/favo...
Feb. 10, 2016 02:15 PM EST Reads: 216
SYS-CON Events announced today that Commvault, a global leader in enterprise data protection and information management, has been named “Bronze Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Commvault is a leading provider of data protection and information management...
Feb. 10, 2016 12:15 PM EST Reads: 429
SYS-CON Events announced today that VAI, a leading ERP software provider, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. VAI (Vormittag Associates, Inc.) is a leading independent mid-market ERP software developer renowned for its flexible solutions and ability to automate critical business functions for the distribution, manufacturing, specialty retail and service sectors. An IBM Premier Business Part...
Feb. 10, 2016 12:00 PM EST Reads: 624
With an estimated 50 billion devices connected to the Internet by 2020, several industries will begin to expand their capabilities for retaining end point data at the edge to better utilize the range of data types and sheer volume of M2M data generated by the Internet of Things. In his session at @ThingsExpo, Don DeLoach, CEO and President of Infobright, will discuss the infrastructures businesses will need to implement to handle this explosion of data by providing specific use cases for filte...
Feb. 10, 2016 11:00 AM EST Reads: 197