How to implement an external service call in a Spring application?

In a Spring application, to call an external service, the RestTemplate class or the more modern WebClient from Spring WebFlux are usually used.

Example using RestTemplate:

@Autowired
private RestTemplate restTemplate;

public String callExternalService() {
    String url = "https://api.example.com/data";
    return restTemplate.getForObject(url, String.class);
}

For this, you need to declare a RestTemplate bean in the configuration:

@Bean
public RestTemplate restTemplate() {
    return new RestTemplate();
}

If using WebClient (reactive client):

@Autowired
private WebClient webClient;

public Mono<String> callExternalService() {
    return webClient.get()
            .uri("https://api.example.com/data")
            .retrieve()
            .bodyToMono(String.class);
}

And the bean:

@Bean
public WebClient webClient() {
    return WebClient.create();
}

Thus, for calling an external REST service in a Spring application, it is convenient to use RestTemplate or WebClient.