Migrate from RestTemplate to WebFlux

I have this RestTemplate which I want to migrate to WebFlux client:

RestTemplate restTemplate = new RestTemplate();
String url = "https://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml";
ResponseEntity<Envelope> response = restTemplate.getForEntity(url, Envelope.class);

I tried this:

Boolean webClient = WebClient.builder()
                .build()
                .get()
                .uri("https://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml")
                .accept(MediaType.APPLICATION_XML)
                .exchangeToMono(res -> Mono.just(res.statusCode().equals(HttpStatus.OK)))
                .timeout(Duration.ofSeconds(2))
                .block();

I'm not clear how I can get the response and read the response as JAVA DTO. Do you know how I have to implement his code?

Solution

To make a request and retrieve a response you need to call the retrieve function on the WebClient. Then you can parse the response Body with bodyToMono. It's important to know that Mono is a single Object and Flux are Collection-Types

Envelope envelope = WebClient.builder()
                .build()
                .get()
                .uri("https://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml")
                .accept(MediaType.APPLICATION_XML)
                .exchangeToMono(res -> Mono.just(res.statusCode().equals(HttpStatus.OK)))
                .timeout(Duration.ofSeconds(2))
                .retrieve()
                .bodyToMono(Envelope.class)
                .block();

There's also a nice example and explanation on this page: https://www.baeldung.com/webflux-webclient-parameters

But I would suggest you to structure your code a little bit more. For example, as you're using Spring Boot think about using that WebClientBuilder to create a WebClient as Bean, that WebClient would be configured to have a base url (https://www.ecb.europa.eu). Then you have a service where you inject that WebClient and make a call to receive your Envelope. Something like this would enable you to use the same WebCLient for different calls to the same host:

import java.util.List;
import java.util.concurrent.TimeUnit;

import io.netty.channel.ChannelOption;
import io.netty.handler.timeout.ReadTimeoutHandler;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.MediaType;
import org.springframework.http.client.reactive.ClientHttpConnector;
import org.springframework.http.client.reactive.ReactorClientHttpConnector;
import org.springframework.stereotype.Service;
import org.springframework.web.reactive.function.client.WebClient;
import reactor.netty.http.client.HttpClient;

@Configuration
public class RestConfig {
    @Bean
    public WebClient ecbEuropaWebClient(WebClient.Builder webClientBuilder) {
        HttpClient httpClient = HttpClient.create().tcpConfiguration(
                (client) -> client.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 2000).doOnConnected(
                        (connection) -> connection.addHandlerLast(
                                new ReadTimeoutHandler(2000, TimeUnit.MILLISECONDS))));
        ClientHttpConnector connector = new ReactorClientHttpConnector(httpClient);
        return webClientBuilder
                .baseUrl("https://www.ecb.europa.eu")
                .clientConnector(connector)
                .build();
    }
}

@Service
public class EcbEuropaService {
    @Autowired
    private WebClient ecbEuropaWebClient;

    public Envelope getEnvelope() {
        return ecbEuropaWebClient.get()
                .uri(uriBuilder -> uriBuilder.path("/stats/eurofxref/eurofxref-daily.xml").build())
                .accept(MediaType.APPLICATION_XML).retrieve().bodyToMono(Envelope.class).block();
    }
}