Some concepts are evergreen, they remain relevant and useful decades after their initiation. The same is true for reactive programming. The concept was first introduced in the 1960s and is now more relevant than ever because of the rise of mobile and web app development.

Here in this guide, we will go through the basics of reactive programming, its benefits for Java applications, and many more things. So, let's dive right into it.

What Is Reactive Programming in Java?

As the concept is very old, over time people have derived different meanings of it. But here we will discuss the most simple meaning that would clearly define the concept and provide better understanding.

A programming model created especially for coping with asynchronous events and the act of generating a change or modification and implementing it in a specific order under an execution environment is called reactive programming.

Let's take an example of a series of events to understand the concept.

James wanted to party on a Friday night in his home. So, he invited his friends and cooked dinner for it. In what ways would he approach?

James finishes all his work early, calls his friends, and goes to the market to buy groceries and essentials for dinner. After arriving home, he starts cooking and once the dinner is ready, he cleans his house. The guests arrive after a while and the party commences.

This is a sync approach where all the tasks are performed in a sequence as a result, the time taken to complete everything will be longer.

James finishes all the work early and invites his friends. He then ordered the food online and cleaned his apartment. The food arrives shortly after that. James starts the party without friends and guests join him shortly afterwards.

This is an async approach.

James completes his work, invites his friends, and orders the food online. He cleans his apartment, receives the food delivery, and waits for friends to arrive and start the party together.

This is the reactive approach to the problem. It is called reactive because you are waiting for the async actions to get finished and then move on to further steps.

Let's say you are in a chemistry lab where you have to combine two chemicals to form a third one. You have to mix them both and wait for a while to allow the reaction to complete and get a new chemical on your hands. Such is the concept of reactive programming.

An Example of Java Reactive Programming

So, you get what Java reactive programming is. But where, when, and how to use this concept? The apps that experience heavy loading or have multiple users need reactive programming. This approach is suitable for the following types of applications:

Gaming apps
Audio and video apps
Social media and chatting platforms

Moreover, reactive programming is helpful for a variety of components in an app including:

Server code with highly interactive user interface elements
Proxy servers and load balancers
Real-time data streaming
AI and ML

It might pique your interest to know that developers at Netflix utilize an open-source reactive programming library from Microsoft called Rx or Reactive Extensions for their web app. Writing asynchronous and complicated programs becomes easier with Rx. Netflix’s web application is reactive because its code reacts differently to different events such as async data gathered from the server, keypresses, mouse clicks, and more.

Normally, the events would be designed as a series of callbacks but thanks to the Rx library, Netflix developers can now design them as a collection of data. It is very helpful because when events are modeled as a collection of data, they can be modified similarly to the transformations with in-memory collections.

Events will then be pushed from producer to consumer asynchronously. Netflix users would then react to the data when made available to them.

How to do Java Reactive Programming?

The Java app performance is enhanced with reactive programming. The blocking calls that result in process and context switches in an OS are avoided to obtain high performance.

When the number of user requests, the number of users, or the requirements of the web applications increases significantly, it is recommended that you adopt the approach of reactive programming for your application.

Reactive programming will consider your workflow to be an async sequence of events. The main four building blocks of Java reactive programming are as follows:

Observables - The Source of the data that emits various numbers of values along with the errors that can be either finite or infinite.
Subscribers - Those who use the Observables. They use the given data. Observables also send completion events and errors to the subscribers.
Operators - They create the Observables. They can also combine, transform, or filter them.
Schedulers - Enables the easy addition of threading to Subscribers and Observables.

When you use reactive programming, the data streams in the spine of your app will convey messages, calls, events, and failures. You can observe this data stream using reactive programming and react whenever a value is emitted.

A developer can create streams of HTTP requests, cache events, click events, and more in the code. These streams are easily changeable. It makes your app asynchronous.

Developers can leverage Rx or Reactive Extensions to compose the async and event-driven programs using an observable sequence and for the effective implementation of reactive programming. Rx is an amazing toolbox that allows you to create, combine, transform, and filter these data streams, which as we learned previously, are Observables.

Enabling the implementation of reactive programming in your application is now possible using several libraries like Rx and Spring.

How is Reactive Programming different from Imperative Programming?

There are two approaches for app development; reactive programming and imperative programming. Java is an imperative programming language. It primarily focuses on achieving desired results. The state of a program can be altered using statements with imperative programming.

The concept of imperative programming is similar to that of natural languages’ imperative mood. If someone wants to do something, commands are conveyed for it. The imperative paradigm is not so different from it.

The imperative program will contain some statements that will tell the computer how to operate the program. Therefore, the code will then be executed as per those commands that describe every single step that the program needs to take to accomplish the objective.

In reactive programming, you have to pull the data. Whereas in imperative programming, you are pushing it. Just because they have their differences doesn't mean you can't use them together. Both paradigms can be used together to fulfill different requirements in the same project.

For example, in many Java applications, reactive programming handles the event management while the business logic is written in an imperative paradigm. This says that although coding can be done in an imperative style, you will need reactive programming to fulfill specific functions of your applications.

Why use Reactive Programming?

Learning reactive programming is not so simple, but once you master it, you can simplify your development tasks in various ways. Some of the benefits of using reactive programming for app development are as mentioned below:

Reactive programming can quickly process large chunks of data so it helps developers enhance the app performance. The reactive programming modules are:

Highly responsive
More flexible
Less latent
Resilient
Efficiently use the resources
More tolerant of failure
Scalable

Being responsive, RP modules are capable of providing interactive and effective feedback to the users. It enhances the user experience.

The code for reactive programming is easy to read and scalable because it is more clear and concise. Therefore, making updates and modifications is very simple here. All of these make reactive programming time-effective. It is also good at handling errors.

Reactive programming comes with an amazing feature called backpressure. So, when a publisher emits the data, this feature allows the user to control its flow. This feature is very helpful in controlling the traffic between the provider and the users. In addition to that, the “out of memory” problem is also solved thanks to the services from backpressure.

Final words

Learning reactive programming can be quite challenging. It takes dedication and hard work just to get a good grasp of the concept. But once mastered, this paradigm can serve you well. Nowadays, there are many applications for reactive programming so naturally, it brings back a lot of benefits as well.

Two things that matter the most are that reactive programming helps with app development by simplifying complicated matters. More importantly, it improves the performance of the application which as a result enhances the user experience. In this digital age, UX is like a crown jewel feature of an application. It helps in personalizing the user journey. So, you can say that reactive programming is most critical for the success of your project.

The Essential Guide to Reactive Programming in Java