Introduction to RxJava Flowable

Kuldeep singh
3 min readJul 3, 2023
Photo by Clément Hélardot on Unsplash

Introduction: RxJava is a popular reactive programming library that brings the concept of Observables and Observers to the Java language. Flowable is an extension of the Observable class in RxJava that is specifically designed to handle backpressure, which occurs when the rate at which data is emitted is faster than the rate at which it can be consumed. In this blog post, we will explore the basics of RxJava Flowable and how it can be used.

What is a Flowable? A Flowable is similar to an Observable in that it represents a stream of data or events that can be observed and processed by Observers. However, Flowable adds the ability to handle backpressure, which is crucial when dealing with large amounts of data or slow consumers. Backpressure refers to the mechanism of controlling the flow of data so that the consumer can process it at its own pace, avoiding overwhelming or dropping data.

Creating a Flowable: Flowables can be created in a similar way to Observables. Here are a few common methods:

  1. Create: The Flowable.create() method allows you to manually create a Flowable. Within the create() method, you define the logic for emitting items to the Observers. For example:
Flowable<String> flowable = Flowable.create(emitter -> {
}, BackpressureStrategy.BUFFER);

2. Just: The Flowable.just() method creates a Flowable that emits a fixed set of items and then completes. For example:

Flowable<Integer> flowable = Flowable.just(1, 2, 3, 4, 5);

3. FromIterable: The Flowable.fromIterable() method creates a Flowable that emits items from an iterable data structure, such as a list or set. For example:

List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
Flowable<String> flowable = Flowable.fromIterable(names);

Subscribing to a Flowable: Observers can subscribe to a Flowable in a similar way to Observables. To handle backpressure, Flowables provide additional options for specifying the backpressure strategy. Here’s an example:

flowable.subscribe(new Subscriber<String>() {
public void onSubscribe(Subscription subscription) {
subscription.request(Long.MAX_VALUE); // Request all items

public void onNext(String item) {
// Handle the emitted item

public void onError(Throwable error) {
// Handle errors

public void onComplete() {
// Handle completion
System.out.println("Flowable completed");

In the above example, the onSubscribe() method is called when the Observer subscribes to the Flowable. To request all items from the Flowable, we use subscription.request(Long.MAX_VALUE). This ensures that the Observer can process all emitted items.

Backpressure Strategies: Flowables provide different backpressure strategies to control how data is emitted and handled when there’s a mismatch in the speed of data production and consumption. Some commonly used backpressure strategies are:

  • BUFFER: Buffers all emitted items until the Observer can consume them.
  • DROP: Drops emitted items if the Observer is unable to keep up.
  • LATEST: Keeps only the latest emitted item and discards previous ones if the Observer is slow.

Operators and Transformations: Similar to Observables, Flowables support a wide range of operators and transformations that can be applied to manipulate emitted items and control the flow of data. These operators include filtering, mapping, combining, and more.

Conclusion: RxJava Flowable is a powerful tool for handling backpressure in reactive programming. It allows developers to deal with large data streams and slow consumers effectively. By understanding the basics of Flowables, creating them, subscribing to them, and applying backpressure strategies, you can manage data flow in a more efficient and controlled manner in your applications.

In this blog post, we’ve covered the fundamentals of RxJava Flowable and demonstrated how to create Flowables, subscribe to them, and handle backpressure. This knowledge will empower you to handle demanding data scenarios and build more robust and scalable applications.



Kuldeep singh

Tech enthusiast. Crafting code that blends innovation with functionality. Exploring tech trends, sharing insights.