Replacing RestTemplate with WebClient

Question

I have a controller that uses RestTemplate to get data from several rest endpoints. Since RestTemplate is blocking, my web page is taking long time to load. In order to increase the performance, I am planning to replace all my usages of RestTemplate with WebClient. One of the methods I currently have that uses RestTemplate is as below.

public List<MyObject> getMyObject(String input){
    URI uri = UriComponentsBuilder.fromUriString("/someurl")
            .path("123456")
            .build()
            .toUri();
    RequestEntity<?> request = RequestEntity.get(uri).build();
    ParameterizedTypeReference<List<MyObject>> responseType =   new ParameterizedTypeReference<List<MyObject>>() {};
    ResponseEntity<List<MyObject>> responseEntity = restTemplate.exchange(request, responseType); 

    MyObject obj = responseEntity.getBody(); 

}

Now I want to replace my above method to use WebClient but I am new to WebClient and not sure where to start. Any direction and help is appreciated.

Answer 1

To help you I am giving you example how we can replace restTemple with webClient. I hope you have already setup your pom.xml

Created a Configuration class.

@Slf4j
@Configuration
public class ApplicationConfig {

    /**
     * Web client web client.
     *
     * @return the web client
     */
    @Bean
    WebClient webClient() {
        return WebClient.builder()
            .filter(this.logRequest())
            .filter(this.logResponse())
            .build();
    }

    private ExchangeFilterFunction logRequest() {
        return ExchangeFilterFunction.ofRequestProcessor(clientRequest -> {
            log.info("WebClient request: {} {} {}", clientRequest.method(), clientRequest.url(), clientRequest.body());
            clientRequest.headers().forEach((name, values) -> values.forEach(value -> log.info("{}={}", name, value)));
            return Mono.just(clientRequest);
        });
    }

    private ExchangeFilterFunction logResponse() {
        return ExchangeFilterFunction.ofResponseProcessor(clientResponse -> {
            log.info("WebClient response status: {}", clientResponse.statusCode());
            return Mono.just(clientResponse);
        });
    }
}

Plus a service class calling WebClient

@Component
@RequiredArgsConstructor
public class MyObjectService {

    private final WebClient webClient;

    public Mono<List<Object>> getMyObject(String input) {
        URI uri = UriComponentsBuilder.fromUriString("/someurl")
            .path("123456")
            .build()
            .toUri();

        ParameterizedTypeReference<List<MyObject>> responseType = new ParameterizedTypeReference<List<MyObject>>() {
        };

        return this.webClient
            .get()
            .uri(uri)
            .exchange()
            .flatMap(response -> response.bodyToMono(responseType));
    }
}

This will give you a non blocking Mono of List<MyObject>, you can also extract body to flux by using response.bodyToFlux(responseType)

I hope this will give you a base to explore more.