restclient-migration

RestTemplate to RestClient Migration Skill

Overview

Spring Framework 6.1 (Spring Boot 3.2+) introduces RestClient, a modern, fluent API for synchronous HTTP requests that replaces the older RestTemplate. While RestTemplate still works, RestClient is the recommended approach for new code.

Key Differences

Migration Examples

1. Basic GET Request

Before (RestTemplate)

@Service
public class ExternalApiService {
    private final RestTemplate restTemplate;

    public ExternalApiService() {
        this.restTemplate = new RestTemplate();
    }

    public Map<String, Object> getUser(String userId) {
        String url = "https://api.example.com/users/" + userId;
        ResponseEntity<Map> response = restTemplate.getForEntity(url, Map.class);
        return response.getBody();
    }
}

After (RestClient)

@Service
public class ExternalApiService {
    private final RestClient restClient;

    public ExternalApiService() {
        this.restClient = RestClient.create();
    }

    public Map<String, Object> getUser(String userId) {
        return restClient.get()
            .uri("https://api.example.com/users/{id}", userId)
            .retrieve()
            .body(new ParameterizedTypeReference<Map<String, Object>>() {});
    }
}

2. POST Request with Body

Before (RestTemplate)

public void sendNotification(String userId, String message) {
    String url = baseUrl + "/notifications";

    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_JSON);
    headers.setAccept(Collections.singletonList(MediaType.APPLICATION_JSON));

    Map<String, String> payload = Map.of(
        "userId", userId,
        "message", message
    );

    HttpEntity<Map<String, String>> request = new HttpEntity<>(payload, headers);
    restTemplate.postForEntity(url, request, Void.class);
}