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.boot.webtestclient.autoconfigure.AutoConfigureWebTestClient;
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)
@AutoConfigureWebTestClient
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!");
    });
  }
}