Welcome!

Industrial IoT Authors: Tom Kelly, Anders Wallgren, Elizabeth White, Liz McMillan, Ian Khan

Related Topics: Java IoT, Industrial IoT, Microservices Expo, IBM Cloud, Weblogic, IoT User Interface

Java IoT: Article

Part 3 | Component Models in Java

Service Component Architecture Model

Service Component Architecture (shortly referred as SCA) is a technology for creating services from components. SCA is a set of OASIS standards and part of it is developed with the collaboration of vendors from open source community, referred as "OSOA" Open SOA. SCA helps to build systems as a collection of interconnected components. The components created in SCA communicate through the services. The advantage of SCA is its neutral component model. It allows services to be built by any language component like Java, C++, BPEL, JavaScript, Ruby, Python etc. SCA addresses two important needs of component world:

  • Complexity
  • Reusability

SCA is best suited model for distributed systems. SCA simplifies building of systems by simple assembling of components. SCA like other component model discussed in the previous sections facilitates component assembly in the middle tier - business tier of N-tier architecture. SCA has some key elements like services, components, composites and domains.

In SCA, applications are created and assembled as components. Components contain the functionality to be exposed to the clients. The functionality provided by the components is exposed as services. Multiple components in the application interact and get bounded by a mechanism called "wire". Components are connected through wire and their services are exposed through a composite.

Several open source tools/IDEs helps to develop SCA application using designer tools. The key elements in SCA are represented through some standard symbols are represented in Figure 1.

Figure 1: SCA Key Elements

 

Services
Services are the functionality provided by the components. They are intended to perform the business function. Services can be implemented in any language like Java, C# and BPEL. Service has two primary attributes:

  • Service Contract
  • Service Address

Service contract defines the methods, input parameters for the methods and the return value. Service contract can be defined in several ways. In Java, service contract is a simple interface (POJI - Plain Old Java Interface) which exposes the functionality of the components. Service contract in Java is usually an interface which can be used locally as well as remotely. The remote service contract will have SCA annotation @Remotable. In SOA world, the service contract is defined as a WSDL file. IDL is also one of the ways to define service contract.

While service contract exposes the functionality provided by the component, Service address is used by the clients to uniquely identify the service. Service address is unique per service. Reusability is achieved through the service address, because clients connect to the service through the service address.

Component
Component provides one or more services. Components contain the business logic for the functionality exposed by service contracts - interfaces. Components can be implemented in any language supported by runtime like Java, C#, BPEL, Ruby, Python etc. Components are implemented as POJOs in Java. The Java class has to implement the Java interface defined as the service contract. Component will have an associated service, optionally a reference and a property. The service is used for exposing the functionality of the component. A reference is another interface contract provided by some other component. Component's dependency on another component is resolved through reference. A property of a component is a configurable parameter which is used to change the behavior of the component dynamically during runtime (with some of its parameters being changed). In the Java class which represents the component, property is specified as an annotation and the reference is also mentioned as an annotation.

Figure 2: Component with Services, References and Properties

Composite
A composite is a XML file which is used for configuring components. The association of the component with the service and the reference is all mentioned in the composite. A composite is the main element which is used for configuring components. The XML file is written using a language called SCDL - Service Component Definition Language which is based on XML. The composite can be written as set of XML elements or can be created using the composite designer tools provided by IDEs.

Figure 3: Composite graphical representation

First a composite is defined, then components are defined as part of it. The services provided are defined as part of the component definition. A composite is used to configure more than one component.

If a component is dependent on another component, then a reference is defined on the component which has dependency. The reference is service contract of the other component. Service and reference are connected using "Wire". Wire acts as a binding element between client component and the target component. The wire binding can be defined as a local or remote binding. The wire binding reference is also configured in the composite. In the implementation, the references to other components are referred using @Reference annotation. The reference of the target component is obtained using dependency injection. The reference dependency injection can be constructor based or setter methods based or field based injection. However the field based injection is concise which is preferred.

If the component's behavior has to be changed during runtime through change in the value of the attributes,  a property can be defined on the composite.

Figure 4: Component Wiring

Domain
Components are created and configured in composite. The composite is deployed in SCA runtime environment called ‘Domain'. A SCA domain is a collection of SCA runtime instances. SCA runtime instances host components in containers. SCA domain allows composites to be deployed as a whole and also individual component. It is possible to deploy components from a composite to be deployed in different runtimes which is purely vendor specific. The domain provides the required services like resource sharing, communication and management to the components deployed in it.

SCA Component Model Example
The SCA component model can be understood with the same shopping Cart example discussed in the models discussed earlier.

Here in this example, there is only a single component called ‘CartServiceComponent'  which exposes its functionality through the CartService interface which is the service contract for the CartServiceComponent. As a first step, the service contract is defined. The CartService interface is a service contract which contains the business methods defined by the component.

package com.online.shopping.intf;

import java.util.Collection;

public interface CartService {
public void addItem(Product product, int quantity);
public Collection<Product> listItems();    
public double getTotalPrice();
public void clearCart();
}

The CartService is implemented by the class CartServiceImpl is a POJO which represents the CartServiceComponent.

package com.online.shopping.impl;

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;

import com.online.shopping.intf.CartService;
import com.online.shopping.intf.Product;

public class CartServiceImpl implements CartService {
Map<Product, Integer> items = new HashMap<Product, Integer>();      
@Override
public void addItem(Product product, int quantity) {
if(items.containsKey(product)) {
quantity +=items.get(product);
}
items.put(product, quantity);
}

@Override
public Collection<Product> listItems() {
return items.keySet();
}

@Override
public double getTotalPrice() {
double totalPrice = 0;
for(Product product: items.keySet()) {
totalPrice+=product.getPrice()* items.get(product);           
}
return totalPrice;
}

@Override
public void clearCart() {
items.clear();
}

}

The service contract and the component are connected using SCA composite designer tool provided by IDEs like Eclipse. Using the tool, a composite is created named ‘Cart.composite'. The composite is an XML file which will have an associated Cart.composite_diagram which represents the composite file as a graphical representation. In the Cart composite diagram, using the component creation tool, a component is created named ‘CartServiceComponent'. A service is added to the composite named ‘CartService'.  Using the designer tool, the Java interface file is dragged and dropped on to the Service defined and the Java implementation class to the CartServiceComponent. The service is promoted using the tool (that is exposing the service for clients to consume it). The graphical representation of composite diagram is as follows:

Figure 5: SCA Component Model - Cart Component Example

The composite file contains XML code that describes the component assembly in the composite diagram.

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<sca:composite xmlns:sca="http://www.osoa.org/xmlns/sca/1.0" name="Cart" targetNamespace="http://eclipse.org/SCACart/Cart">
<sca:component name="CartServiceComponent">
<sca:implementation.java
class="com.online.shopping.impl.CartServiceImpl"/>

<sca:service name="CartService">
<sca:interface.java
interface="com.online.shopping.intf.CartService"/>
</sca:service>

</sca:component>

<sca:service name="CartService"         
promote="CartServiceComponent/CartService"/>

</sca:composite>

The CartServiceComponent is created and assembled. The component is deployed in SCADomain as a single component with the id ‘CartService'. This is evident from the <sca:service> element having an attribute called ‘promote' in the composite XML file. The SCADomain is the runtime for the SCA components. In this example, Apache Tuscany is the runtime used for deploying composite. The client for the CartServiceComponent first looks up for the composite in the SCADomain where it is deployed. From the domain, client looks for the service with the service address and the service contract. Once it gets the service reference, the client consumes the methods exposed by the component.

package com.client.shopping;

import java.util.Collection;

import org.apache.tuscany.sca.host.embedded.SCADomain;

import com.online.shopping.intf.CartService;
import com.online.shopping.intf.Product;

public class CartClient {

public static void main(String arg[]) {
SCADomain scaDomain = SCADomain.newInstance("Cart.composite");
CartService cartService = scaDomain.getService(
CartService.class, "CartServiceComponent");

Product product = new Product();
product.setName("OSGi");
product.setPrice(550.00);
cartService.addItem(product, 20);

Product newProduct = new Product();
newProduct.setName("SCA");
newProduct.setPrice(300.00);
cartService.addItem(newProduct, 10);

Collection<Product> productItems = cartService.listItems();
for(Product items: productItems) {
System.out.println(items.getName()+"******"+ items.getPrice());             
}            

System.out.println("Total Price of Cart Items: "+cartService.getTotalPrice());

cartService.clearCart();
}
}

Thus SCA component model provides easy steps for creating and assembling components. Assembling components is easy by linking the reference to the service of the target components. SCA promotes reuse through service contracts and address and solves complexity through loose coupling. SCA as a component model promotes reusability and it is highly preferred for assembly if components. The advantage of SCA is its language neutral for several languages like Java, C#, Ruby etc.

Summary
Componentization provides several advantages. The component models play an important role in developing, deploying and assembling of components for an application. Component models provide a simpler way for component reference and look up and hence making the development easier.

In this article we discussed about four latest component models in Java - Enterprise JavaBeans, Spring, OSGi and SCA in brief. We understand that each component model has its own standards for development and assembly. The runtime environment provided by these component framework helps in execution of the components developed using the appropriate model. We also tried to understand the similarity and differences of these component models through a simple component ‘Cart' component which is part of online shopping application.

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.

More Stories By S Sangeetha

S Sangeetha is a Senior Technical Architect at the E-Commerce Research Labs at Infosys Limited. She has over 15 years of experience in architecture, design and development of enterprise Java applications. She is also involved in enhancing the technical skills of Architects at Infosys. She has co-authored a book on ‘J2EE Architecture’ and also has written numerous articles on Java for various online Java forums like JavaWorld, java.net, DevX.com and internet.com. She can be reached at [email protected]

Comments (0)

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.


@ThingsExpo Stories
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...
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...
Fortunately, meaningful and tangible business cases for IoT are plentiful in a broad array of industries and vertical markets. These range from simple warranty cost reduction for capital intensive assets, to minimizing downtime for vital business tools, to creating feedback loops improving product design, to improving and enhancing enterprise customer experiences. All of these business cases, which will be briefly explored in this session, hinge on cost effectively extracting relevant data from ...
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...
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...
As enterprises work to take advantage of Big Data technologies, they frequently become distracted by product-level decisions. In most new Big Data builds this approach is completely counter-productive: it presupposes tools that may not be a fit for development teams, forces IT to take on the burden of evaluating and maintaining unfamiliar technology, and represents a major up-front expense. In his session at @BigDataExpo at @ThingsExpo, Andrew Warfield, CTO and Co-Founder of Coho Data, will dis...
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...
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...
With the Apple Watch making its way onto wrists all over the world, it’s only a matter of time before it becomes a staple in the workplace. In fact, Forrester reported that 68 percent of technology and business decision-makers characterize wearables as a top priority for 2015. Recognizing their business value early on, FinancialForce.com was the first to bring ERP to wearables, helping streamline communication across front and back office functions. In his session at @ThingsExpo, Kevin Roberts...
SYS-CON Events announced today that Fusion, a leading provider of cloud services, 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. Fusion, a leading provider of integrated cloud solutions to small, medium and large businesses, is the industry's single source for the cloud. Fusion's advanced, proprietary cloud service platform enables the integration of leading edge solutions in the cloud, including clou...
Most people haven’t heard the word, “gamification,” even though they probably, and perhaps unwittingly, participate in it every day. Gamification is “the process of adding games or game-like elements to something (as a task) so as to encourage participation.” Further, gamification is about bringing game mechanics – rules, constructs, processes, and methods – into the real world in an effort to engage people. In his session at @ThingsExpo, Robert Endo, owner and engagement manager of Intrepid D...
Eighty percent of a data scientist’s time is spent gathering and cleaning up data, and 80% of all data is unstructured and almost never analyzed. Cognitive computing, in combination with Big Data, is changing the equation by creating data reservoirs and using natural language processing to enable analysis of unstructured data sources. This is impacting every aspect of the analytics profession from how data is mined (and by whom) to how it is delivered. This is not some futuristic vision: it's ha...
WebRTC has had a real tough three or four years, and so have those working with it. Only a few short years ago, the development world were excited about WebRTC and proclaiming how awesome it was. You might have played with the technology a couple of years ago, only to find the extra infrastructure requirements were painful to implement and poorly documented. This probably left a bitter taste in your mouth, especially when things went wrong.
Learn how IoT, cloud, social networks and last but not least, humans, can be integrated into a seamless integration of cooperative organisms both cybernetic and biological. This has been enabled by recent advances in IoT device capabilities, messaging frameworks, presence and collaboration services, where devices can share information and make independent and human assisted decisions based upon social status from other entities. In his session at @ThingsExpo, Michael Heydt, founder of Seamless...
The IoT's basic concept of collecting data from as many sources possible to drive better decision making, create process innovation and realize additional revenue has been in use at large enterprises with deep pockets for decades. So what has changed? In his session at @ThingsExpo, Prasanna Sivaramakrishnan, Solutions Architect at Red Hat, discussed the impact commodity hardware, ubiquitous connectivity, and innovations in open source software are having on the connected universe of people, thi...
WebRTC: together these advances have created a perfect storm of technologies that are disrupting and transforming classic communications models and ecosystems. In his session at WebRTC Summit, Cary Bran, VP of Innovation and New Ventures at Plantronics and PLT Labs, provided an overview of this technological shift, including associated business and consumer communications impacts, and opportunities it may enable, complement or entirely transform.
There are so many tools and techniques for data analytics that even for a data scientist the choices, possible systems, and even the types of data can be daunting. In his session at @ThingsExpo, Chris Harrold, Global CTO for Big Data Solutions for EMC Corporation, showed how to perform a simple, but meaningful analysis of social sentiment data using freely available tools that take only minutes to download and install. Participants received the download information, scripts, and complete end-t...
For manufacturers, the Internet of Things (IoT) represents a jumping-off point for innovation, jobs, and revenue creation. But to adequately seize the opportunity, manufacturers must design devices that are interconnected, can continually sense their environment and process huge amounts of data. As a first step, manufacturers must embrace a new product development ecosystem in order to support these products.
Manufacturing connected IoT versions of traditional products requires more than multiple deep technology skills. It also requires a shift in mindset, to realize that connected, sensor-enabled “things” act more like services than what we usually think of as products. In his session at @ThingsExpo, David Friedman, CEO and co-founder of Ayla Networks, discussed how when sensors start generating detailed real-world data about products and how they’re being used, smart manufacturers can use the dat...
When it comes to IoT in the enterprise, namely the commercial building and hospitality markets, a benefit not getting the attention it deserves is energy efficiency, and IoT’s direct impact on a cleaner, greener environment when installed in smart buildings. Until now clean technology was offered piecemeal and led with point solutions that require significant systems integration to orchestrate and deploy. There didn't exist a 'top down' approach that can manage and monitor the way a Smart Buildi...