Springboot 3.x - Reactive programming (2)

三、WebFlux

Blocking Web vs. Reactive Web

Blocking Web (Servlet) and Reactive Web (WebFlux) have significant differences in several aspects.

1. Front Controller

• Servlet-Blocking Web: Uses DispatcherServlet as the front controller to handle all HTTP requests.
• WebFlux-Reactive Web: Uses DispatcherHandler as the front controller to handle all HTTP requests.

2. Handler

• Servlet-Blocking Web: Uses Controller as the handler.
• WebFlux-Reactive Web: Uses WebHandler or Controller as the handler.

3. Request and Response

• Servlet-Blocking Web: Uses ServletRequest and ServletResponse.
• WebFlux-Reactive Web: Uses ServerWebExchange, along with ServerRequest and ServerResponse.

4. Filters

• Servlet-Blocking Web: Uses Filter (e.g., HttpFilter).
• WebFlux-Reactive Web: Uses WebFilter.

5. Exception Handlers

• Servlet-Blocking Web: Uses HandlerExceptionResolver to handle exceptions.
• WebFlux-Reactive Web: Uses DispatchExceptionHandler to handle exceptions.

6. Web Configuration

• Servlet-Blocking Web: Configured via @EnableWebMvc.
• WebFlux-Reactive Web: Configured via @EnableWebFlux.

7. Custom Configuration

• Servlet-Blocking Web: Uses WebMvcConfigurer.
• WebFlux-Reactive Web: Uses WebFluxConfigurer.

8. Return Types

• Servlet-Blocking Web: The return type can be any object.
• WebFlux-Reactive Web: The return type can be a Mono, a Flux, or any object.

9. Sending REST Requests

• Servlet-Blocking Web: Uses RestTemplate to send REST requests.
• WebFlux-Reactive Web: Uses WebClient to send REST requests.

Core Difference Between Blocking and Reactive Models

Blocking Model (Servlet): Each request is handled by a dedicated thread, which waits for operations to complete (such as database queries or IO operations). This model can lead to thread exhaustion under high concurrency, affecting system performance.

Reactive Model (WebFlux): Uses a non-blocking IO model with a small number of threads handling many requests. It leverages callback mechanisms, event-driven architecture, and asynchronous non-blocking IO for efficient resource utilization and high concurrency handling. Key features of the reactive programming model include:

• Non-blocking Operations: Operations do not block the current thread, allowing it to continue processing other tasks.
• Callback Mechanism: Handles subsequent steps through callback mechanisms once an operation completes.
• Event-driven Architecture: Processes requests based on an event-driven approach.

This model is more efficient in resource usage and is suitable for scenarios requiring high concurrency and large traffic volumes.

Summary

The choice between a blocking or reactive web framework depends on specific application scenarios and requirements. If the application is primarily I/O-intensive with high concurrency needs, then WebFlux is a more suitable choice; if it involves CPU-intensive tasks, the traditional Servlet model might be more appropriate.

四、Integration with Springboot

Spring WebFlux is the new reactive web framework introduced in Spring Framework 5.0. Unlike Spring MVC, it does not require the servlet API, is fully asynchronous and non-blocking, and implements the Reactive Streams specification through the Reactor project.

Spring WebFlux comes in two flavors: functional and annotation-based. The annotation-based one is quite close to the Spring MVC model, as shown in the following example:

import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;@RestController
@RequestMapping("/users")
public class MyRestController {private final UserRepository userRepository;private final CustomerRepository customerRepository;public MyRestController(UserRepository userRepository, CustomerRepository customerRepository) {this.userRepository = userRepository;this.customerRepository = customerRepository;}@GetMapping("/{userId}")public Mono<User> getUser(@PathVariable Long userId) {return this.userRepository.findById(userId);}@GetMapping("/{userId}/customers")public Flux<Customer> getUserCustomers(@PathVariable Long userId) {return this.userRepository.findById(userId).flatMapMany(this.customerRepository::findByUser);}@DeleteMapping("/{userId}")public Mono<Void> deleteUser(@PathVariable Long userId) {return this.userRepository.deleteById(userId);}}

“WebFlux.fn”, the functional variant, separates the routing configuration from the actual handling of the requests, as shown in the following example:

import org.springframework.boot.SpringBootConfiguration;
import org.springframework.context.annotation.Bean;
import org.springframework.http.MediaType;
import org.springframework.web.reactive.function.server.RequestPredicate;
import org.springframework.web.reactive.function.server.RouterFunction;
import org.springframework.web.reactive.function.server.ServerResponse;import static org.springframework.web.reactive.function.server.RequestPredicates.accept;
import static org.springframework.web.reactive.function.server.RouterFunctions.route;/*** <B>Main class name：</B>MyRoutingConfiguration<BR>* <B>Summary description：</B>WebFlux router configuration class<BR>* @author Chris.Gou* @since 2024/07/19 14:53:40*/
@SpringBootConfiguration(proxyBeanMethods = false)
public class MyRoutingConfiguration {/*** RequestPredicate is an interface that defines a request predicate, that is, a condition for testing HTTP requests. <BR/>* Here, ACCEPT_JSON defines a predicate that checks whether the Accept header of the request is application/json.*/private static final RequestPredicate ACCEPT_JSON = accept(MediaType.APPLICATION_JSON);/*** RouterFunction<ServerResponse> is an interface that represents a routing function that routes a request to a handler and returns a ServerResponse.* @param userHandler* @return*/@Beanpublic RouterFunction<ServerResponse> monoRouterFunction(MyUserHandler userHandler) {return route() // route() is a static method that returns a RouterFunctions.Builder for building routing functions..GET("/{user}", ACCEPT_JSON, userHandler::getUser).GET("/{user}/customers", ACCEPT_JSON, userHandler::getUserCustomers).DELETE("/{user}", ACCEPT_JSON, userHandler::deleteUser).build();}}

import org.springframework.stereotype.Component;
import org.springframework.web.reactive.function.server.ServerRequest;
import org.springframework.web.reactive.function.server.ServerResponse;
import reactor.core.publisher.Mono;/*** <B>Main class name：</B>MyUserHandler<BR>* <B>Summary description：</B>MyUserHandler<BR>* @author Chris.Gou* @since 2024/07/19 15:02:47*/
@Component
public class MyUserHandler {public Mono<ServerResponse> getUser(ServerRequest request) {// Business processingreturn null;}public Mono<ServerResponse> getUserCustomers(ServerRequest request) {// Business processingreturn null;}public Mono<ServerResponse> deleteUser(ServerRequest request) {// Business processingreturn null;}
}

These route definitions enable applications to implement specific business logic by routing requests to corresponding handler methods based on different URL patterns and HTTP methods.