Basic Introduction to Spring WebFlux

Spring WebFlux is a reactive, non-blocking web framework that uses Project Reactor's reactive streams API to enable highly concurrent and asynchronous processing of web requests in a non-blocking and event-driven way. It is fully asynchronous and non-blocking using reactive streams and callbacks.

• It uses Project Reactor as the underlying reactive library for composable asynchronous and event-based programming.
• The core abstraction is around reactive streams - publishers that provide push-based asynchronous streams of data.
• Controllers return Publisher or Mono types instead of ModelAndView. Responses are streamed back incrementally.
• It is optimized for non-blocking and event-driven applications on modern servers like Netty and Undertow.

In this article, we will explore the advantages and disadvantages of Spring WebFlux – a non-blocking web framework.

Flow of Spring WebFlux

• A client sends an HTTP request to the server which is handled by the Netty/Undertow server.
• The server dispatches the request to the Spring WebFlux dispatcher handler.
• The dispatcher handler routes the request to the appropriate controller based on the request path.
• The controller returns a Mono or Flux type which will emit a stream of responses asynchronously.
• The dispatcher handler wraps the Mono/Flux in a ServerResponse and returns it.
• The serverResponse is streamed back to the client incrementally as the Mono/Flux emits values, without blocking threads.
• Any exceptions are caught and handled gracefully instead of blocking threads.
• The client receives the response asynchronously without the server blocking on I/O.

Core principles of Spring WebFlux

• Asynchronous operations: All I/O operations like database access, network calls etc are asynchronous and non-blocking. This prevents threads from blocking on I/O.
• Reactive streams: Data is processed and consumed asynchronously as streams of multiple values over time rather than single blocking responses.
• Reactive Streams compliance: WebFlux is built on Project Reactor which implements Reactive Streams. This allows asynchronous and non-blocking processing of data streams.
• Non-blocking requests: The underlying server (Netty by default) is fully asynchronous and non-blocking. It can handle many more requests concurrently without blocking threads.

Key Features of Spring WebFlux

• Non-blocking I/O: Uses asynchronous and non-blocking I/O to avoid blocking threads, enabling high concurrency.
• Reactive streams support: Fully implements Reactive Streams specification using Project Reactor for reactive programming.
• Functional programming model: Controllers return Mono/Flux publishers instead of blocking responses, favoring functional style.
• Server-sent events: Supports server-sent events out of the box for real-time full-duplex communication.
• WebSockets: Built-in support for WebSockets to enable real-time bidirectional communication.
• Reactive database access: Seamless integration with reactive databases like MongoDB, Cassandra, Redis etc.
• Caching support: Supports caching responses using Cache API in a non-blocking manner.

Advantages of WebFlux

• Scalability: It can handle more requests concurrently using less resources due to non-blocking I/O. This improves scalability.
• Responsiveness: Applications remain highly responsive even under heavy load since requests are not blocked waiting for I/O.
• Resource efficiency: Fewer threads are required to handle the same number of requests than blocking applications.
• Resiliency: Failure of one request impacts only some. Backpressure prevents overloading.

Disadvantages of WebFlux

• Debugging challenges: Asynchronous code can be more difficult to debug compared to sequential blocking code.
• Complexity: Reactive code involving streams, and callbacks can become more complex than simple blocking code.
• Latency sensitivity: Reactive applications require consistently low latency to perform well compared to blocking.
• Migration effort: Existing blocking code needs to be refactored for non-blocking APIs, which requires time and effort.

Use Cases of WebFlux

• Financial trading systems
• Real-time collaboration tools
• Video/audio streaming Platforms
• Live tracking systems

Difference between Spring WebFlux and Spring MVC

As Spring WebFlux is an alternative of Spring MVC, so let us know the core differences between them.