Click here to close now.

Welcome!

XML Authors: Carmen Gonzalez, Liz McMillan, Dana Gardner, Glenn Rossman, Lori MacVittie

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

Java: Article

Componentizing Applications with Layered Architecture

Componentization facilitates modularity and easy maintenance

A component is a reusable software entity that is developed and deployed independently. Component based software development has many architectural advantages. In the previous article Componentizing a Monolithic Application in Java, we learnt the need for componentizing applications for getting the benefits of reusability and modularity. In this article let us look at how multi layered application can be componentized. We take the example of a multi-layered POS (Point-Of-Sale) application and understand how the application can be componentized at various layers like presentation, business and persistence layers.

Point of Sale - An Example Application
Consider a Point-of-Sale (POS) application meant for tracking orders and payments in a restaurant. The POS is used to track the tables being occupied by the guests, orders being made from various tables, and to print bills. Apart from these operational features, the POS application can also be used for restaurant administration. Total number of tables in the restaurant, list of foods sold in the restaurant, their prices, and the associated tax rates can be managed. The use cases to be supported by the POS application are described in brief below:

  • Guests Check-in - This use case is invoked by the waiters when new guests arrive at the restaurant. POS displays a list of empty tables, and the waiter chooses an empty table and seats the guests in that table.
  • Place Order - When guests from a table order for food, waiter invokes this use case. POS prompts the waiter for the table number, food item, and quantity ordered. POS consolidates and maintains orders against each table.
  • Modify Order - Waiter can modify the quantity of any order already placed.
  • Cancel Order - Waiter can cancel any order already placed.
  • Pay Bill - Waiter invokes this use case to print the bill and collect payment for all items ordered from a table.
  • Guests Check-out - When guests from a table leave, waiter invokes this usecase to mark the table as empty.
  • Collections Report - At any point of time, the POS user can look at all the past payments collected.

Existing Implementation of POS
The existing implementation of POS uses a typical layered architecture pattern consisting of presentation layer, business layer, and data layer. The layered architecture is supported by the MVC (Model-View-Controller) design pattern. In the MVC paradigm, Model is responsible to capture real world business information through software objects. View is responsible to present the business information captured by Model visually for human consumption. Controller is responsible to handle user inputs and mediate between View and Model.

Figure 1 - Existing POS Application Architecture

 

Figure 2 - Objects in POS Application Layers

In the layered architecture of POS, Views and Controllers belong to the Presentation layer. Information exchange across the layer borders is enabled by the Model objects carrying business domain data. The multiple layers of POS are shown in Figure 1. The arrow directions indicate the control flow, or in other words, direction of invocation across layers. Figure 2 expands on Figure 1 and provides the list of objects present in each layer.

Model Objects
Model objects carry the business domain relevant information. In the restaurant business domain, we have Food, Table, Order, Bill, and TableConfig model objects. In addition, there is a FoodCategory that each Food belongs to, an OrderItem, a collection of which makes up an order, and a BillLineItem, a collection of which belongs to a Bill.

Figure 3 - Model Objects

All the model objects are presented in Figure 3. Food object is responsible for carrying information such as food name, price, tax rate, and the food category. The table object is responsible for storing the table number and the status on whether the table is occupied or empty. If the table is occupied, the table stores an Order object associated with the table. The Order object captures items ordered from the table. Each OrderItem is an order for multiple quantities of a food item. The payment toward all the items ordered from a table is captured and persisted in the form of a Bill object. Each OrderItem in Order has a corresponding BillLineItem in the Bill.

Presentation Layer
The presentation is based on a console-based UI in the current POS implementation. The presentation layer consists of Views and Controllers. Each UI view is responsible for showing one screen to the user and collecting input from the user interactively. The controller objects are responsible for processing the input gathered by the UI view objects. In addition, the controllers also control the UI screen flow - they direct the next UI screen to be shown after each screen based on user input. To process the input given by the users, the controller objects depend on business objects in the Business Layer.

Business Layer
The business layer contains objects that implement the business logic rules. The controllers from the presentation layer make use of the services offered by this layer. There are  four business objects in the business layer, which are presented below:

  • FoodBiz - FoodBiz is responsible for business logic associated with food creation, modification, and categorization.
  • OrderBiz - It implements all the business logic associated with maintaining orders placed by guests in different tables, addition and modification of order items, and cancellation of ordered items.
  • TableBiz - It is responsible for maintaining total number of tables based on configuration, blocking and releasing tables based on guests check-in and checkout.
  • BillBiz - This object is responsible for printing bill, and persisting bill details for future reference.

Business objects that need to persist the model data objects depend on the persistence layer.

Persistence Layer
The persistence layer is responsible for transfering the state information stored in the model objects to a persistent storage and for retrieving it back to in-memory objects. This layer consists of Data Access Objects (DAO). DAO interfaces are defined for TableConfig, Food, and Bill objects. Concrete DAO objects implement these interfaces specific to the database used. The example code that accompanies this article uses Db4o database. Each of the generic DAO is implemented by the Db4o specific concrete DAO object.

Componentization
Having analyzed the existing application in depth, which provides all the required functionalities, why should we componentize this application? Componentization in general helps in two different endeavors: (i) improve maintainability and (ii) extract reusable parts for storage and future reuse.

Let's investigate the maintainability aspect. Assume that there is a new business rule imposed in the POS application. The POS is supposed to charge a gratuity of 15% for any guest group consisting of eight or more members. On analysis of the existing application architecture, the BillBiz is the right object that can shoulder this new responsibility, because BillBiz implements the business logic that calculates the Bill amount. The BillBiz class diagram is presented in Figure 4.

Figure 4 - BillBiz Class Diagram

The BillBiz object has a payBill(Table table):Bill method. This method implements the business logic for billing. This method can be modified to accommodate the gratuity-related business change. In addition to this change, the calculated gratuity for each bill needs to be captured in some model object and persisted. The PayBillUI class in the presentation layer also needs to be changed to display the gratuity amount.

If we make these changes in the existing application as is, we need to recompile and redeploy the whole application, even though the application has a layered architecture. This is because these layers are logical and not physical. Moreover, to isolate the impact of the new business requirement, we need to isolate the Billing functionality from other functionality such as Order Management and Food Management functionality. Let's see how componentization can address this maintenance issue.

Componentized POS Application
Let's split the business layer of the POS into four different components as shown in Figure 5. By splitting the application into different components, the Billing responsibility is isolated into the Bill component.

Figure 5 - Functional Componentization of POS

In the componentized structure in Figure 5, when a new business rule for Billing is required, the Bill component can be replaced with a new Bill component without affecting rest of the application. In order to achieve the component structure proposed in Figure 6, we package the objects from the original implementation into different component packages as per Table 1.

Component

Objects

Layer

GuestUI

CheckInUI

CheckOutUI

CheckInCtrlr

CheckOutCtrlr

Presentation

AdminUI

AdminUI

FoodAdminUI

TableAdminUI

FoodAdminCtrlr

TableAdminCtrlr

Presentation

OrderUI

OrderUI

OrderCtrlr

Presentation

BillUI

PayBillUI

PayBillCtrlr

Presentation

Table

TableBiz

TableDAO

Business & Data

Food

FoodBiz

FoodDAO

Business & Data

Order

OrderBiz

OrderDAO

Business & Data

Bill

BillBiz

BillDAO

Business & Data

Table 1 - Mapping of New Components to Old Objects and Layers

As a general pattern, it can be observed that each UI component consists of necessary view and controller objects. Each business component consists of necessary business objects and DAO objects for persistence. Apart from these components, the objects from the Model are packaged together as an object library, which is referred by each of these components. The objects inside the Model library are listed in Table 2. These are the same model objects that were presented in Figure 3.

Model Object Library

Objects

Model

Table

Food

Order

Bill

FoodCategory

OrderItem

BillLineItem

Table 2 - Objects inside the Model Object library

Once we repackage the objects from the existing implementation into components as discussed above, we get component architecture for the POS application as shown in Figure 7. In the diagram the connector with a lollipop and a receptacle represents a component assembly between two components. In a component assembly, one component exposes a service and another component consumes that service. For example, the Table component exposes TableBiz service which is consumed by all the other components.

Figure 6 - Functional Componentization of POS

Figure 8 provides an expanded view of Figure 7, providing inside details of each component.

Figure 7 - Inside individual component

Replacing a Bill Component
As discussed earlier, we have a business rule change request that requires an additional gratuity amount to be charged to those guest groups whose size is eight or larger. We had reasoned in the earlier analysis that the business logic change can be implemented in the BillBiz class in the Bill component, in the payBill() method. Part of the code from this method is presented in Figure 8.

Figure 8 - Code Snippet from payBill(Table table):Bill method of BillBiz

As can be seen from the code snippet in Figure 8, the payBill() method obtains the Order object associated with the Table for which the Bill has to be generated. For each OrderItem in the Order, a BillLineItem is generated. For each BillLineItem, the base price, tax, and total price are calculated. All BillLineItems are kept in a collection that becomes part of the generated Bill object. The Bill object also has a total base price, total tax, and total payable amount. These values are calculated as sums of corresponding price components of the constituent bill line items. In the business logic change request, the total price of the bill should have an additional component called gratuity, if the number of guests is equal to or more than 8.

The current total price of the bill is given by:

Total Price = Base Price + Tax

With the introduction of gratutity, this would have to be changed to

Total Price = Base Price + Tax + Gratuity

Gratuity = 0.15 * Base Price (if number of guests >=8)

= 0 (otherwise)

The payBill() method code snippet shown in Figure 8 can be modified to accommodate the above change. However, we need to capture the new gratuity element in the model objects. In order to give least interference to other components, we introduce a new model object called as Gratuity. This object is responsible for storing the gratuityAmount and the Bill object to which the gratuityAmount is applicable. The class diagram of Gratuity is presented below.

Figure 9 - Gratuity Object in the Model

We shall call the modified Bill component as Bill2, and the modified BillUI component as BillUI2. The modified payBill method that implements the addition of a gratuity component to the bill is shown in Figure 10.

Figure 10 - Modified Code Snippet from payBill(Table table):Bill method of BillBiz

As can be seen in Figure 8 and Figure 10, the new code has created a Gratuity object if the number of guests is equal to or more than eight. It has also added a necessary amount to the total amount in the Bill object. The BillUI2 component would retrieve the Gratuity object associated with the bill and display the gratuity amount if it is non-zero. To facilitate this retrieval, a new method called getGratuityForBill() is added to BillBiz class in the Bill2 component. The modified BillBiz class is shown in Figure 11.

Figure 11 - Modified BillBiz Class in Bill2 Component

We reassemble the POS application by substituting Bill and BillUI components with the Bill2 and BillUI2 components. Of course, the new Model object library is to be used. With these changes, the component architecture of the application is presented in Figure 12.

Figure 12 - Modified Component Architecture of POS Application

At any point, the Bill2 and BillUI2 components can be replaced with the old Bill and BillUI components to change the behavior of the application back to the old. Thus evolution of the application with the insertion and removal of new functionalities can be done by changing components in the application assembly without changing the application code.

Conclusion
Componentization provides many benefits. In this article we demonstrated how a multi-layered POS application can be componentized. One of the important properties of a component is its pluggable nature. In the POS example, we saw how componentization facilitates modularity and easy maintenance through asimple replacement of pluggable components.

Acknowledgments
The authors would like to sincerely thank Anupama Nithyanand for her support and Nitin KL  for his valuable suggestions and reviewing this article. Authors are indebted to Soumya Bardhan, Shikhar Johari and Vishal Verma for helping in the development and testing efforts of the sample 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
The true value of the Internet of Things (IoT) lies not just in the data, but through the services that protect the data, perform the analysis and present findings in a usable way. With many IoT elements rooted in traditional IT components, Big Data and IoT isn’t just a play for enterprise. In fact, the IoT presents SMBs with the prospect of launching entirely new activities and exploring innovative areas. CompTIA research identifies several areas where IoT is expected to have the greatest impact.
The Internet of Things (IoT) is rapidly in the process of breaking from its heretofore relatively obscure enterprise applications (such as plant floor control and supply chain management) and going mainstream into the consumer space. More and more creative folks are interconnecting everyday products such as household items, mobile devices, appliances and cars, and unleashing new and imaginative scenarios. We are seeing a lot of excitement around applications in home automation, personal fitness, and in-car entertainment and this excitement will bleed into other areas. On the commercial side, m...
Advanced Persistent Threats (APTs) are increasing at an unprecedented rate. The threat landscape of today is drastically different than just a few years ago. Attacks are much more organized and sophisticated. They are harder to detect and even harder to anticipate. In the foreseeable future it's going to get a whole lot harder. Everything you know today will change. Keeping up with this changing landscape is already a daunting task. Your organization needs to use the latest tools, methods and expertise to guard against those threats. But will that be enough? In the foreseeable future attacks w...
Disruptive macro trends in technology are impacting and dramatically changing the "art of the possible" relative to supply chain management practices through the innovative use of IoT, cloud, machine learning and Big Data to enable connected ecosystems of engagement. Enterprise informatics can now move beyond point solutions that merely monitor the past and implement integrated enterprise fabrics that enable end-to-end supply chain visibility to improve customer service delivery and optimize supplier management. Learn about enterprise architecture strategies for designing connected systems tha...
Dale Kim is the Director of Industry Solutions at MapR. His background includes a variety of technical and management roles at information technology companies. While his experience includes work with relational databases, much of his career pertains to non-relational data in the areas of search, content management, and NoSQL, and includes senior roles in technical marketing, sales engineering, and support engineering. Dale holds an MBA from Santa Clara University, and a BA in Computer Science from the University of California, Berkeley.
Wearable devices have come of age. The primary applications of wearables so far have been "the Quantified Self" or the tracking of one's fitness and health status. We propose the evolution of wearables into social and emotional communication devices. Our BE(tm) sensor uses light to visualize the skin conductance response. Our sensors are very inexpensive and can be massively distributed to audiences or groups of any size, in order to gauge reactions to performances, video, or any kind of presentation. In her session at @ThingsExpo, Jocelyn Scheirer, CEO & Founder of Bionolux, will discuss ho...
The cloud is now a fact of life but generating recurring revenues that are driven by solutions and services on a consumption model have been hard to implement, until now. In their session at 16th Cloud Expo, Ermanno Bonifazi, CEO & Founder of Solgenia, and Ian Khan, Global Strategic Positioning & Brand Manager at Solgenia, will discuss how a top European telco has leveraged the innovative recurring revenue generating capability of the consumption cloud to enable a unique cloud monetization model to drive results.
As organizations shift toward IT-as-a-service models, the need for managing and protecting data residing across physical, virtual, and now cloud environments grows with it. CommVault can ensure protection &E-Discovery of your data – whether in a private cloud, a Service Provider delivered public cloud, or a hybrid cloud environment – across the heterogeneous enterprise. In his session at 16th Cloud Expo, Randy De Meno, Chief Technologist - Windows Products and Microsoft Partnerships, will discuss how to cut costs, scale easily, and unleash insight with CommVault Simpana software, the only si...
Docker is an excellent platform for organizations interested in running microservices. It offers portability and consistency between development and production environments, quick provisioning times, and a simple way to isolate services. In his session at DevOps Summit at 16th Cloud Expo, Shannon Williams, co-founder of Rancher Labs, will walk through these and other benefits of using Docker to run microservices, and provide an overview of RancherOS, a minimalist distribution of Linux designed expressly to run Docker. He will also discuss Rancher, an orchestration and service discovery platf...
Analytics is the foundation of smart data and now, with the ability to run Hadoop directly on smart storage systems like Cloudian HyperStore, enterprises will gain huge business advantages in terms of scalability, efficiency and cost savings as they move closer to realizing the potential of the Internet of Things. In his session at 16th Cloud Expo, Paul Turner, technology evangelist and CMO at Cloudian, Inc., will discuss the revolutionary notion that the storage world is transitioning from mere Big Data to smart data. He will argue that today’s hybrid cloud storage solutions, with commodity...
Cloud data governance was previously an avoided function when cloud deployments were relatively small. With the rapid adoption in public cloud – both rogue and sanctioned, it’s not uncommon to find regulated data dumped into public cloud and unprotected. This is why enterprises and cloud providers alike need to embrace a cloud data governance function and map policies, processes and technology controls accordingly. In her session at 15th Cloud Expo, Evelyn de Souza, Data Privacy and Compliance Strategy Leader at Cisco Systems, will focus on how to set up a cloud data governance program and s...
Roberto Medrano, Executive Vice President at SOA Software, had reached 30,000 page views on his home page - http://RobertoMedrano.SYS-CON.com/ - on the SYS-CON family of online magazines, which includes Cloud Computing Journal, Internet of Things Journal, Big Data Journal, and SOA World Magazine. He is a recognized executive in the information technology fields of SOA, internet security, governance, and compliance. He has extensive experience with both start-ups and large companies, having been involved at the beginning of four IT industries: EDA, Open Systems, Computer Security and now SOA.
The industrial software market has treated data with the mentality of “collect everything now, worry about how to use it later.” We now find ourselves buried in data, with the pervasive connectivity of the (Industrial) Internet of Things only piling on more numbers. There’s too much data and not enough information. In his session at @ThingsExpo, Bob Gates, Global Marketing Director, GE’s Intelligent Platforms business, to discuss how realizing the power of IoT, software developers are now focused on understanding how industrial data can create intelligence for industrial operations. Imagine ...
Every innovation or invention was originally a daydream. You like to imagine a “what-if” scenario. And with all the attention being paid to the so-called Internet of Things (IoT) you don’t have to stretch the imagination too much to see how this may impact commercial and homeowners insurance. We’re beyond the point of accepting this as a leap of faith. The groundwork is laid. Now it’s just a matter of time. We can thank the inventors of smart thermostats for developing a practical business application that everyone can relate to. Gone are the salad days of smart home apps, the early chalkb...
We certainly live in interesting technological times. And no more interesting than the current competing IoT standards for connectivity. Various standards bodies, approaches, and ecosystems are vying for mindshare and positioning for a competitive edge. It is clear that when the dust settles, we will have new protocols, evolved protocols, that will change the way we interact with devices and infrastructure. We will also have evolved web protocols, like HTTP/2, that will be changing the very core of our infrastructures. At the same time, we have old approaches made new again like micro-services...
Operational Hadoop and the Lambda Architecture for Streaming Data Apache Hadoop is emerging as a distributed platform for handling large and fast incoming streams of data. Predictive maintenance, supply chain optimization, and Internet-of-Things analysis are examples where Hadoop provides the scalable storage, processing, and analytics platform to gain meaningful insights from granular data that is typically only valuable from a large-scale, aggregate view. One architecture useful for capturing and analyzing streaming data is the Lambda Architecture, representing a model of how to analyze rea...
Today’s enterprise is being driven by disruptive competitive and human capital requirements to provide enterprise application access through not only desktops, but also mobile devices. To retrofit existing programs across all these devices using traditional programming methods is very costly and time consuming – often prohibitively so. In his session at @ThingsExpo, Jesse Shiah, CEO, President, and Co-Founder of AgilePoint Inc., discussed how you can create applications that run on all mobile devices as well as laptops and desktops using a visual drag-and-drop application – and eForms-buildi...
SYS-CON Events announced today that Vitria Technology, Inc. will exhibit at SYS-CON’s @ThingsExpo, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Vitria will showcase the company’s new IoT Analytics Platform through live demonstrations at booth #330. Vitria’s IoT Analytics Platform, fully integrated and powered by an operational intelligence engine, enables customers to rapidly build and operationalize advanced analytics to deliver timely business outcomes for use cases across the industrial, enterprise, and consumer segments.
Containers and microservices have become topics of intense interest throughout the cloud developer and enterprise IT communities. Accordingly, attendees at the upcoming 16th Cloud Expo at the Javits Center in New York June 9-11 will find fresh new content in a new track called PaaS | Containers & Microservices Containers are not being considered for the first time by the cloud community, but a current era of re-consideration has pushed them to the top of the cloud agenda. With the launch of Docker's initial release in March of 2013, interest was revved up several notches. Then late last...
SYS-CON Events announced today that Dyn, the worldwide leader in Internet Performance, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Dyn is a cloud-based Internet Performance company. Dyn helps companies monitor, control, and optimize online infrastructure for an exceptional end-user experience. Through a world-class network and unrivaled, objective intelligence into Internet conditions, Dyn ensures traffic gets delivered faster, safer, and more reliably than ever.