WebFlux REST API と WebClient

package com.example.reactivewebservice;

public record Greeting(String message) {
}

package com.example.reactivewebservice;

import org.springframework.http.MediaType;
import org.springframework.stereotype.Component;
import org.springframework.web.reactive.function.BodyInserters;
import org.springframework.web.reactive.function.server.ServerRequest;
import org.springframework.web.reactive.function.server.ServerResponse;

import reactor.core.publisher.Mono;

@Component
public class GreetingHandler {

	public Mono<ServerResponse> hello(ServerRequest request) {
		return ServerResponse.ok().contentType(MediaType.APPLICATION_JSON)
			.body(BodyInserters.fromValue(new Greeting("Hello, Spring!")));
	}
}

package com.example.reactivewebservice;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.MediaType;
import org.springframework.web.reactive.function.server.RouterFunction;
import org.springframework.web.reactive.function.server.RouterFunctions;
import org.springframework.web.reactive.function.server.ServerResponse;

import static org.springframework.web.reactive.function.server.RequestPredicates.GET;
import static org.springframework.web.reactive.function.server.RequestPredicates.accept;

@Configuration(proxyBeanMethods = false)
public class GreetingRouter {

	@Bean
	public RouterFunction<ServerResponse> route(GreetingHandler greetingHandler) {

		return RouterFunctions.route(GET("/hello")
				.and(accept(MediaType.APPLICATION_JSON)), greetingHandler::hello);
	}
}

package com.example.reactivewebservice;

import reactor.core.publisher.Mono;

import org.springframework.http.MediaType;
import org.springframework.stereotype.Component;
import org.springframework.web.reactive.function.client.WebClient;

@Component
public class GreetingClient {

	private final WebClient client;

	// Spring Boot auto-configures a WebClient.Builder instance with nice defaults and customizations.
	// We can use it to create a dedicated WebClient for our component.
	public GreetingClient(WebClient.Builder builder) {
		this.client = builder.baseUrl("http://localhost:8080").build();
	}

	public Mono<String> getMessage() {
		return this.client.get().uri("/hello").accept(MediaType.APPLICATION_JSON)
				.retrieve()
				.bodyToMono(Greeting.class)
				.map(Greeting::message);
	}

}

package com.example.reactivewebservice;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

@SpringBootApplication
public class ReactiveWebServiceApplication {

	public static void main(String[] args) {
		ConfigurableApplicationContext context = SpringApplication.run(ReactiveWebServiceApplication.class, args);
		GreetingClient greetingClient = context.getBean(GreetingClient.class);
		// We need to block for the content here or the JVM might exit before the message is logged
		System.out.println(">> message = " + greetingClient.getMessage().block());
	}
}

package com.example.reactivewebservice;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.http.MediaType;
import org.springframework.test.web.reactive.server.WebTestClient;

import static org.assertj.core.api.Assertions.assertThat;

//  We create a @SpringBootTest, starting an actual server on a RANDOM_PORT
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class GreetingRouterTest {

	// Spring Boot will create a WebTestClient for you,
	// already configure and ready to issue requests against "localhost:RANDOM_PORT"
	@Autowired
	private WebTestClient webTestClient;

	@Test
	public void testHello() {
		webTestClient
			// Create a GET request to test an endpoint
			.get().uri("/hello")
			.accept(MediaType.APPLICATION_JSON)
			.exchange()
			// and use the dedicated DSL to test assertions against the response
			.expectStatus().isOk()
			.expectBody(Greeting.class).value(greeting -> {
				assertThat(greeting.message()).isEqualTo("Hello, Spring!");
		});
	}
}