Welcome!

IBM Cloud Authors: Scott Allen, Jose Diaz, John Esposito, Pat Romanski, Liz McMillan

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

Java IoT: Article

Componentizing a Monolithic Application in Java

Using a simple homegrown component model and framework

Component-oriented development has many architectural advantages. In spite of this, many developers tend to solve problems the monolithic way on the first go. This article demonstrates how a monolithic design can be modified to achieve component-based design. During this conversion process, the necessity of Component Models and Frameworks are highlighted. The article demonstrates the componentization of an example monolithic application using a simple homegrown component model and framework developed by the authors.

Introducing E-Store - A Business Application
Let us assume that we need to implement a simple E-store business application. The application needs to cater to the following simple business use cases for a single actor - the consumer.

  • Browse the catalog of products - Consumer can browse through the items in the store. E-store app displays the different products available in the store along with their price
  • Buy one or more products - User adds one or more quantities of a product to the shopping cart. If sufficient stock is available, E-Store app adds the selected items to the shopping cart
  • Check-out - User can checkout with the items in the shopping cart. E-store app displays the total price of all the items in the shopping cart. Subsequently, stock quantities of the purchased items are reduced

Monolithic Implementation of E-Store
The E-Store application explained above can be realized with the help of the classes shown in Figure 1.

Figure 1: Class Diagram for E-Store Application

The implementation of the above design in source code and binary code form can be obtained from the links provided at the end of the article. The implementation of the monolithic application is explained briefly in the sections below.

Application Startup - UI
The monolithic E-Store application starts up with the UI class main method. During its startup, the UI class instantiates the Store (E-Store) class. The code snippet corresponding to this is shown in Listing 1.

public class UI {

static Store estore = new Store();

public static void main(String[] args) {
int userChoice = mainMenu();
...
}
...
}

Listing 1: Startup Code - UI Class

The E-Store class instantiates the Inventory and ShoppingCart classes during its startup as shown in Listing 2.

public class Store {

Inventory inventory = new Inventory();
ShoppingCart shoppingCart = new ShoppingCart();
...
}

Listing 2: Startup Code - E-Store Class

The inventory class initializes the stock during its instantiation, by creating instances of Product class objects. The code snippet is shown in Listing 3

public class Inventory {

private Map<Product, Integer> stock = new HashMap<Product, Integer>();

public Inventory() {initStock();}

private void initStock() {
Product newIPad = new Product("NewIPad", 400.00);
stock.put(newIPad, 50);

Product galaxyTab2 = new Product("GalaxyTab2", 300.00);
stock.put(galaxyTab2, 75);

Product kindleFire = new Product("KindleFire", 250.00);
stock.put(kindleFire, 30);
}
...

}

Listing 3: Startup Code - Inventory Initialization

Once the startup is done, the UI class presents a console based menu as shown in Listing 4.

Welcome to eStore!
------------------------

1. Browse Catalog
2. Buy Items
3. Check Out
4. Exit

Choose an option:
1

Listing 4: Console based UI Menu

When the user chooses any one of the options, the UI class calls upon its implementation in the E-Store business class. The implementation of each of these is explained briefly in next few sections.

Browse Catalog Use case Realization
The getCatalog() method in the E-Store class implements this use case. When the getCatalog() method in E-Store class is called, it fetches the list of products from Inventory and returns the same. Code snippet is shown in Listing 5.

public Collection<Product> getCatalog() {

return inventory.getProducts();

}

Listing 5: E-Store Class - getCatalog() implementation

Buy Items Use case Realization
The buyItem() method in the E-Store class implements this use case. The UI class calls this method by passing the name of the product chosen by the user, and the quantity he wants to buy. If sufficient quantity is available in stock, the item is added to the shopping cart and the method returns success; otherwise, the method returns failure and no item is added to shopping cart. The code snippet is presented in Listing 6.

public boolean buyItem(String name, int quantity) {
Product product = inventory.getProduct(name);
if (product == null) return false;

if (inventory.getStock(product) >= quantity) {
shoppingCart.addItem(product, quantity);
return true;
}
return false;
}

Listing 6: E-Store Class - buyItem() implementation

Check Out Use Case Realization
The checkout() method in the E-Store class implements this use case. It reduces the stock in the inventory by the quantity bought. It also returns the total price to be paid by the user. This implementation is shown in Listing 7.

public double checkOut() {
for(Product product : shoppingCart.getItems()) {
int quantity = shoppingCart.getCount(product);
inventory.reduceStock(product, quantity);
}
double price = shoppingCart.getTotalPrice();
shoppingCart.clearItems();
return price;

}

Listing 7: E-Store Class - checkOut() Implementation

What's wrong with the Monolithic implementation?
The initial implementation of E-Store discussed above fulfills all the functional requirements of the application laid down earlier. Still this is not considered as architecturally sound application design because all the classes in the application are tightly coupled to each other. Consider the dependency metrics shown in the table below:

Table 1: Class dependency details

No.

Class

Depends On

# of Dependencies

Dependency Depth

1.

Product

 

0

0

2.

Inventory

Product

1

1

3.

ShoppingCart

Product

1

1

4.

EStore

Inventory, ShoppingCart, Product

3

2

5.

UI

EStore, Product

2

3

 

 

 

 

 

The tight coupling results in high resistance to change in implementation. For example, any change to Product class will require complete change in the application.

Let us say that the E-Store likes to announce promotional sale for three days. During these three days, the total price of the shopping cart should be discounted by 10%. In order to achieve this, we need to change the ShoppingCart class implementation. When the ShoppingCart class is changed, the E-Store class also needs to be recompiled. When the E-Store class is recompiled, the UI class also needs to be recompiled.

What happens at the end of the promotional sale when the E-Store wants to discontinue the discounts? We need to recompile all the 3 classes one more time. Ideally, since the changes affect only the ShoppingCart behavior, rest of the application modules should not have been affected. But due to the tight coupling, other modules are also affected.

Loosening the Coupling through Componentization
Low coupling design principle suggests that there should not be tight coupling among unstable entities. Having dependency on a relatively stable entity does not bring forth the evils of tight coupling.

In order to make the application modules loosely coupled, we need to componentize the application. A component is a deployable piece of software that would be independently developed and independently maintained. Independence here refers to development and maintenance of a component independent of the other components which collaborate with this component in an application assembly. In a component based application, change to one component should not directly affect the application.

We avoid tight coupling between components by introducing the abstraction of Component Interface. A component interface exposes the signature of the functionalities implemented by component. The Component Interface will be a relatively stable entity as compared to the Component Implementation.

A component consumes interfaces that it depends on for fulfilling the required functionality and provides interfaces for the functionality it provides. For collaboration with the other components, the component would work through the interfaces provided by the other components. Practically, the component should not depend on the implementation of the other components; it should depend only on the interfaces provided by those components. This way, the coupling among components is through the relatively stable interfaces and not through the highly instable implementations. Thus the principle of low coupling is upheld.

In addition to the low coupling achieved, componentization of a monolithic application also brings about substitutability of components. This means a component of the application can be substituted by another component without affecting the overall application. The only requirement is that the replacing component must offer the same set of interfaces as was offered by the component being replaced.

Componentizing the E-Store Application
We need to introduce the Component Interface abstraction in the monolithic design shown in Figure 1. Looking at the dependency details represented in the Table 1, the Product, ShoppingCart, Inventory and Store classes should be represented as components. From the implementation classes of Product, Inventory, ShoppingCart, and Store, we can extract Java Interfaces IProduct, IInventory, IShoppingCart, and IStore respectively using the refactoring tools in the IDE. The extracted interfaces are shown in Figure 2. It must be noted in Figure 9 that the method signatures in IInventory, IShoppingCart, and IStore are changed to refer to IProduct interface in place of the Product class in the corresponding methods in Figure 1.

Figure 2: E-Store Interfaces - Class Diagram

In this E-Store application, there are four components represented by their interfaces - IProduct, IInventory, IShoppingCart and IStore. After the interfaces are extracted from the monolithic implementation, it will be a good design to get these interfaces packaged into a separate Java Package called estore.ifce.

The package can also be compiled to a JAR resulting in a deployable and independently maintainable estore.ifce module. This module does not implement any component, but it simply defines ONLY the interfaces which would be implemented by other components in the application. All the components depend ONLY on this common interface module and they need not depend on individual implementation components.

Following the above principle, if we separate the implementation of Product, Inventory, ShoppingCart, and Store into individual packages and into individual JARs, we get the  package structure shown in Figure 3.

Figure 3: Package Diagram separating interface from implementation

When we refactor the code into multiple components as shown above, two code segments fail to compile as shown in Figure 4 and Figure 5. Kindly look at Listings 2 and 3 for reference.

Figure 4: Compilation error in Inventory class post Componentization

Figure 5: Compilation error in Store class post Componentization

The compilation errors occurred due to the fact that above code tried to invoke the implementation code of other components directly. We have arranged our dependencies such that one component would not depend on the internal implementation of the other component. The above code violates this.

This problem can be solved in various ways. This is where all the component models and frameworks come to the rescue. Component models like RMI, EJB, Spring, OSGi and SCA have their own way of creating object references to components from the interfaces. Users can choose to use one of these frameworks or models for initializing the component. However in this article, we will look at a simple component model developed to solve this problem without using any of the component models and frameworks. This component model uses some of the principles of design pattern and best practices which is explained in detail below.

The problem of direct reference to implementation can be resolved by introducing a ‘Factory' object that can be used by the component to obtain an object of the corresponding type. A generalized Factory object could have a signature as below:

public interface IFactory<T> {
public T createInstance();

}

To avoid tight coupling, the Factory object is really useful. So, instead of coupling to a concrete class which implements IProduct, the Inventory implementation can depend on a Factory object of type IFactory<IProduct>. By invoking the createInstance() method on the factory object, the Inventory class can obtain new IProduct objects. Similarly the IInventory and IShoppingCart objects can be obtained from the respective Factory objects using createInstance() method in the Store class.

IProduct iPad = productFactory.createInstance();
.....
IShoppingCart shoppingCart = shoppingCartFactory.createInstance();
IInventory inventory = inventoryFactory.createInstance();

To obtain a factory object, a FactoryRegistry class is used as a common factory registry for registering and retrieving factory objects using the whiteboard pattern. The common registry object can be implemented as shown in Listing 8.

public class FactoryRegistry {

private static Map<Class<?>, IFactory<?>> factoryMap = new HashMap<Class<?>, IFactory<?>>();

public static void registerFactory(Class<?> ifceClazz, IFactory<?> factory) {
factoryMap.put(ifceClazz, factory);
}

public static IFactory<?> getFactory(Class<?> ifceClazz) {
return factoryMap.get(ifceClazz);
}
}

Listing 8: FactoryRegistry Class

The Inventory class can obtain a reference to a product factory object of type IFactory<IProduct> using the whiteboard pattern. Similarly any factory object can be retrieved from the FactoryRegistry.

IFactory<IProduct> productFactory =
(IFactory<IProduct>) FactoryRegistry.getFactory(IProduct.class);

One important question that remains unanswered is how, where and when these factory objects are registered with the FactoryRegistry. All component implementations only try to GET references. As mentioned earlier, component models like RMI, EJB, OSGi have their own service repository where these references are registered and components using these references look up the repository to get an object of the corresponding type. In this simple model, a registry program named ‘ComponentRunner' is handwritten which will look up for IFactory type interfaces and its implementations and register them appropriately so that getFactory method returns an initialized factory object. Kindly refer to the source code provided for details on ComponentRunner.

Implementation of this model will help in resolving the compilation issue highlighted in Figures 4 and 5. The modified code without any compilation error using the factory pattern and registry lookup is shown in Listings 9 and 10.

private void initStock() {

IFactory<IProduct> productFactory = (IFactory<IProduct>) FactoryRegistry.getFactory(IProduct.class);

IProduct iPad = productFactory.createInstance();
iPad.setName("NewIPad");
iPad.setPrice(400.00);
stock.put(iPad, 50);

IProduct gTab = productFactory.createInstance();
gTab.setName("GalaxyTab2");
gTab.setPrice(300.00);
stock.put(gTab, 75);

IProduct kindle = productFactory.createInstance();
kindle.setName("KindleFire");
kindle.setPrice(250.00);
stock.put(kindle, 30);

}

Listing 9: Modified Inventory Class without compilation error

public class Store implements IStore {

IInventory inventory;
IShoppingCart shoppingCart;

public Store() {
IFactory<IInventory> inventoryFactory = (IFactory<IInventory>) FactoryRegistry.getFactory(IInventory.class);
IFactory<IShoppingCart> shoppingCartFactory = (IFactory<IShoppingCart>) FactoryRegistry.getFactory(IShoppingCart.class);

shoppingCart = shoppingCartFactory.createInstance();
inventory = inventoryFactory.createInstance();
}
......

Listing 10: Modified E-Store Class without compilation error

Apart from the above highlighted modifications, the business logic implementation in the components remains the same as before in the monolithic case.

Executing the Sample Application
The sample application demonstrated in this article is available as a zip file for download. The zip file contains a complete Eclipse Workspace with the source as well as binary files. To run the componentized version of this application, it is required to follow the steps below:

  1. Create a folder named ‘run'.
  2. Export the components - store, product, inventory, shopping cart, component model, store app projects from the eclipse workspace to a Jar file in the ‘run' folder, say ‘eStore.jar' for example. In order to reuse these components in other applications, individual projects can be exported as separate jar files.
  3. Copy the contents of ‘bin' folder from comprunner project to the ‘run' folder. The bin folder contains a sub folder named ‘comprunner' which contains the ComponentRunner class.
  4. Open a command prompt and change the directory to ‘run' folder.
  5. To execute the ComponentRunner, type the following in command prompt

Conclusion
The advantage of a component-oriented approach is well explained with a sample application. In this article, we also saw the limitations of having a monolithic application and how the dependencies bring in tight coupling between components. Low coupling between components can be achieved by the abstraction of Component interface. Interfaces also bring in component substitutability. A component can depend on some interfaces and provide interfaces. Interface is the key mechanism in component design principles. Initialization of component implementations can happen using several mechanisms which are different for different component models and frameworks. In this sample, a home grown component model - a factory based model is used for initializing the components and component references are registered with a simple repository - CompRunner for look up.

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 sangeethas@infosys.com.

Comments (1)

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
In his session at @ThingsExpo, Chris Klein, CEO and Co-founder of Rachio, will discuss next generation communities that are using IoT to create more sustainable, intelligent communities. One example is Sterling Ranch, a 10,000 home development that – with the help of Siemens – will integrate IoT technology into the community to provide residents with energy and water savings as well as intelligent security. Everything from stop lights to sprinkler systems to building infrastructures will run ef...
We’ve worked with dozens of early adopters across numerous industries and will debunk common misperceptions, which starts with understanding that many of the connected products we’ll use over the next 5 years are already products, they’re just not yet connected. With an IoT product, time-in-market provides much more essential feedback than ever before. Innovation comes from what you do with the data that the connected product provides in order to enhance the customer experience and optimize busi...
Manufacturers are embracing the Industrial Internet the same way consumers are leveraging Fitbits – to improve overall health and wellness. Both can provide consistent measurement, visibility, and suggest performance improvements customized to help reach goals. Fitbit users can view real-time data and make adjustments to increase their activity. In his session at @ThingsExpo, Mark Bernardo Professional Services Leader, Americas, at GE Digital, will discuss how leveraging the Industrial Interne...
The increasing popularity of the Internet of Things necessitates that our physical and cognitive relationship with wearable technology will change rapidly in the near future. This advent means logging has become a thing of the past. Before, it was on us to track our own data, but now that data is automatically available. What does this mean for mHealth and the "connected" body? In her session at @ThingsExpo, Lisa Calkins, CEO and co-founder of Amadeus Consulting, will discuss the impact of wea...
Increasing IoT connectivity is forcing enterprises to find elegant solutions to organize and visualize all incoming data from these connected devices with re-configurable dashboard widgets to effectively allow rapid decision-making for everything from immediate actions in tactical situations to strategic analysis and reporting. In his session at 18th Cloud Expo, Shikhir Singh, Senior Developer Relations Manager at Sencha, will discuss how to create HTML5 dashboards that interact with IoT devic...
Whether your IoT service is connecting cars, homes, appliances, wearable, cameras or other devices, one question hangs in the balance – how do you actually make money from this service? The ability to turn your IoT service into profit requires the ability to create a monetization strategy that is flexible, scalable and working for you in real-time. It must be a transparent, smoothly implemented strategy that all stakeholders – from customers to the board – will be able to understand and comprehe...
Artificial Intelligence has the potential to massively disrupt IoT. In his session at 18th Cloud Expo, AJ Abdallat, CEO of Beyond AI, will discuss what the five main drivers are in Artificial Intelligence that could shape the future of the Internet of Things. AJ Abdallat is CEO of Beyond AI. He has over 20 years of management experience in the fields of artificial intelligence, sensors, instruments, devices and software for telecommunications, life sciences, environmental monitoring, process...
The IoTs will challenge the status quo of how IT and development organizations operate. Or will it? Certainly the fog layer of IoT requires special insights about data ontology, security and transactional integrity. But the developmental challenges are the same: People, Process and Platform. In his session at @ThingsExpo, Craig Sproule, CEO of Metavine, will demonstrate how to move beyond today's coding paradigm and share the must-have mindsets for removing complexity from the development proc...
A critical component of any IoT project is the back-end systems that capture data from remote IoT devices and structure it in a way to answer useful questions. Traditional data warehouse and analytical systems are mature technologies that can be used to handle large data sets, but they are not well suited to many IoT-scale products and the need for real-time insights. At Fuze, we have developed a backend platform as part of our mobility-oriented cloud service that uses Big Data-based approache...
trust and privacy in their ecosystem. Assurance and protection of device identity, secure data encryption and authentication are the key security challenges organizations are trying to address when integrating IoT devices. This holds true for IoT applications in a wide range of industries, for example, healthcare, consumer devices, and manufacturing. In his session at @ThingsExpo, Lancen LaChance, vice president of product management, IoT solutions at GlobalSign, will teach IoT developers how t...
Digital payments using wearable devices such as smart watches, fitness trackers, and payment wristbands are an increasing area of focus for industry participants, and consumer acceptance from early trials and deployments has encouraged some of the biggest names in technology and banking to continue their push to drive growth in this nascent market. Wearable payment systems may utilize near field communication (NFC), radio frequency identification (RFID), or quick response (QR) codes and barcodes...
SYS-CON Events announced today that Peak 10, Inc., a national IT infrastructure and cloud services 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. Peak 10 provides reliable, tailored data center and network services, cloud and managed services. Its solutions are designed to scale and adapt to customers’ changing business needs, enabling them to lower costs, improve performance and focus inter...
We're entering the post-smartphone era, where wearable gadgets from watches and fitness bands to glasses and health aids will power the next technological revolution. With mass adoption of wearable devices comes a new data ecosystem that must be protected. Wearables open new pathways that facilitate the tracking, sharing and storing of consumers’ personal health, location and daily activity data. Consumers have some idea of the data these devices capture, but most don’t realize how revealing and...
The demand for organizations to expand their infrastructure to multiple IT environments like the cloud, on-premise, mobile, bring your own device (BYOD) and the Internet of Things (IoT) continues to grow. As this hybrid infrastructure increases, the challenge to monitor the security of these systems increases in volume and complexity. In his session at 18th Cloud Expo, Stephen Coty, Chief Security Evangelist at Alert Logic, will show how properly configured and managed security architecture can...
There is an ever-growing explosion of new devices that are connected to the Internet using “cloud” solutions. This rapid growth is creating a massive new demand for efficient access to data. And it’s not just about connecting to that data anymore. This new demand is bringing new issues and challenges and it is important for companies to scale for the coming growth. And with that scaling comes the need for greater security, gathering and data analysis, storage, connectivity and, of course, the...
The IETF draft standard for M2M certificates is a security solution specifically designed for the demanding needs of IoT/M2M applications. In his session at @ThingsExpo, Brian Romansky, VP of Strategic Technology at TrustPoint Innovation, will explain how M2M certificates can efficiently enable confidentiality, integrity, and authenticity on highly constrained devices.
So, you bought into the current machine learning craze and went on to collect millions/billions of records from this promising new data source. Now, what do you do with them? Too often, the abundance of data quickly turns into an abundance of problems. How do you extract that "magic essence" from your data without falling into the common pitfalls? In her session at @ThingsExpo, Natalia Ponomareva, Software Engineer at Google, will provide tips on how to be successful in large scale machine lear...
You think you know what’s in your data. But do you? Most organizations are now aware of the business intelligence represented by their data. Data science stands to take this to a level you never thought of – literally. The techniques of data science, when used with the capabilities of Big Data technologies, can make connections you had not yet imagined, helping you discover new insights and ask new questions of your data. In his session at @ThingsExpo, Sarbjit Sarkaria, data science team lead ...
SYS-CON Events announced today that Ericsson has been named “Gold Sponsor” of SYS-CON's @ThingsExpo, which will take place on June 7-9, 2016, at the Javits Center in New York, New York. Ericsson is a world leader in the rapidly changing environment of communications technology – providing equipment, software and services to enable transformation through mobility. Some 40 percent of global mobile traffic runs through networks we have supplied. More than 1 billion subscribers around the world re...
You deployed your app with the Bluemix PaaS and it's gaining some serious traction, so it's time to make some tweaks. Did you design your application in a way that it can scale in the cloud? Were you even thinking about the cloud when you built the app? If not, chances are your app is going to break. Check out this webcast to learn various techniques for designing applications that will scale successfully in Bluemix, for the confidence you need to take your apps to the next level and beyond.