How do you handle CORS in Spring applications?

Table of Contents

• Introduction
• Key Differences Between Spring MVC and Spring WebFlux Routing
  • 1. Programming Model: Blocking vs. Non-blocking
  • 2. Routing Mechanism
  • 3. Concurrency Model
  • 4. Performance and Scalability
  • 5. Controller Style
  • 6. Use Case
• Summary of Differences
• Conclusion

Introduction

In the Spring ecosystem, both Spring MVC and Spring WebFlux provide routing capabilities for handling HTTP requests in web applications. However, the underlying architecture and approach to routing differ significantly due to the fundamental differences between blocking (imperative) and non-blocking (reactive) programming models. Understanding the differences between Spring MVC routing and Spring WebFlux routing is crucial when choosing the right framework for your application, especially when considering scalability, performance, and use cases for reactive programming.

This guide will compare Spring MVC routing and Spring WebFlux routing, highlighting their key differences and use cases.

Key Differences Between Spring MVC and Spring WebFlux Routing

1. Programming Model: Blocking vs. Non-blocking

• Spring MVC:
  • Spring MVC follows the imperative programming model, which is blocking by nature. Each HTTP request is processed in a sequential manner, meaning that the thread handling a request is blocked until the response is generated. It processes one request at a time on a dedicated thread.
  • This model is ideal for traditional web applications where requests are relatively light, and the resources are managed efficiently.
• Spring WebFlux:
  • Spring WebFlux is built around the reactive programming model and non-blocking I/O. It leverages Reactive Streams to handle requests asynchronously. This means that the processing thread is not blocked while waiting for I/O operations (e.g., database calls, external API requests), allowing the thread to handle other tasks during the wait.
  • WebFlux is designed for highly scalable applications that need to handle many concurrent connections with minimal resource consumption.

2. Routing Mechanism

• Spring MVC Routing:

  • In Spring MVC, routing is based on traditional Servlet-based request handling. Routing is mapped to a controller method through annotations such as @RequestMapping, @GetMapping, @PostMapping, etc.
  • The routing mechanism works well in the imperative model, where each request is processed sequentially by the controller method.

  Example in Spring MVC:

• Spring WebFlux Routing:

  • Spring WebFlux uses a reactive router function to handle routing. Instead of the traditional @RequestMapping annotations, WebFlux leverages the RouterFunction API to create a more declarative way of routing requests.
  • Routes are typically defined using a functional style approach with RouterFunction and HandlerFunction, making it more flexible, composable, and suitable for reactive flows.

  Example in Spring WebFlux:

3. Concurrency Model

• Spring MVC:
  • Spring MVC uses a one-thread-per-request model. A dedicated thread from the servlet container (e.g., Tomcat) is assigned to process each incoming HTTP request.
  • The server thread is blocked for the duration of the request processing (including any I/O operations), making it inefficient in scenarios where there are large numbers of concurrent requests, especially when waiting for external I/O like databases or web services.
• Spring WebFlux:
  • WebFlux is designed for asynchronous, non-blocking processing using reactive streams. The routing mechanism and handlers in WebFlux do not block the I/O thread. Instead, they rely on reactive constructs like Mono and Flux, which allow processing multiple requests concurrently without blocking threads.
  • WebFlux uses event loops and reactive runtimes (like Netty, Undertow, or Servlet 3.1+ containers supporting asynchronous processing) to achieve better scalability and handle thousands of concurrent requests without significant thread overhead.

4. Performance and Scalability

• Spring MVC:
  • Spring MVC’s thread-per-request model can lead to performance issues when scaling horizontally or dealing with a large number of simultaneous requests. Each request ties up a thread, which limits the number of requests the system can handle concurrently.
  • For applications with high traffic, particularly I/O-bound workloads like external API calls or database queries, this approach is not optimal.
• Spring WebFlux:
  • WebFlux offers better performance and scalability due to its non-blocking I/O and event-driven architecture. Since it doesn’t block threads while waiting for external operations (e.g., database queries, HTTP requests), it can handle a significantly higher number of concurrent requests with fewer threads.
  • WebFlux shines in applications with high throughput and long-running I/O-bound operations, such as real-time applications, streaming services, and API gateways.

5. Controller Style

• Spring MVC:
  • Controllers in Spring MVC are typically defined with annotations such as @Controller or @RestController and methods annotated with request mapping annotations like @RequestMapping, @GetMapping, @PostMapping, etc.
  • The controller is expected to return a synchronous result, either a view name (String) or a response body.
• Spring WebFlux:
  • In Spring WebFlux, you can use either annotated controllers (@RestController, @RequestMapping) or functional endpoints (RouterFunction with HandlerFunction).
  • Methods in controllers or handlers return reactive types like Mono (for single-value responses) or Flux (for multiple values). This makes WebFlux ideal for handling asynchronous processing.

6. Use Case

• Spring MVC:
  • Spring MVC is typically used in traditional web applications where requests are not expected to be highly concurrent or require extensive asynchronous processing.
  • It is best suited for CRUD applications, server-side rendered pages, and applications with moderate traffic.
• Spring WebFlux:
  • Spring WebFlux is designed for high-performance, reactive web applications. It is ideal for scenarios where high concurrency, real-time streaming, or long-running operations (e.g., waiting for external APIs or databases) are common.
  • WebFlux is preferred for microservices architectures, API gateways, and event-driven architectures where scalability is critical.

Summary of Differences

Feature	Spring MVC	Spring WebFlux
Programming Model	Imperative (blocking)	Reactive (non-blocking)
Routing Mechanism	@RequestMapping, @GetMapping, etc.	RouterFunction and HandlerFunction
Concurrency	One thread per request (blocking)	Non-blocking I/O, reactive streams
Performance	Limited scalability, blocking threads	High scalability, handles large number of concurrent requests
Controller Style	@Controller, @RestController	@Controller or functional routing (using RouterFunction)
Use Case	Traditional web apps, CRUD applications	Real-time, high concurrency, event-driven apps

Conclusion

The choice between Spring MVC and Spring WebFlux largely depends on the type of application you're building. Spring MVC is suited for traditional, synchronous web applications, while Spring WebFlux is designed for reactive, non-blocking applications that require high scalability and low-latency request handling.

If your application has a high number of concurrent connections, especially with long I/O waits (like waiting on a database or remote APIs), Spring WebFlux offers a more efficient and scalable solution. On the other hand, if your app doesn’t require the complexities of reactive programming and your traffic is relatively predictable, Spring MVC remains a solid, simple choice.