@RestController
@RequiredArgsConstructor
@Validated  // (1)
public class GetAddressController {
    private final GetAddressApiClient client;

    @GetMapping("/get/address")
    public GetAddressResponse getAddress(@ZipCode @RequestParam("zipcode") String zipCode) {  // (1)
        return GetAddressResponse.create(client.request(zipCode));
    }
}

@Documented
@Constraint(validatedBy = {})
@Target(PARAMETER)
@Retention(RUNTIME)
@Pattern(regexp = "[0-9]{3}[-]{0,1}[0-9]{4}")  // (2)
public @interface ZipCode {
    String message() default "";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

@RestControllerAdvice  // (3)
public class CommonExceptionHandler {

    @ExceptionHandler(ConstraintViolationException.class)  // (3)
    public ResponseEntity handleConstraintViolationException(ConstraintViolationException ex) {
        GetAddressResponse response = new GetAddressResponse(
                "400",
                "入力された郵便番号が不正です。",
                null
        );
        return new ResponseEntity<>(response, HttpStatus.BAD_REQUEST);  // (4)
    }
}

@Component
public class GetAddressApiClient {
    private final RestTemplate restTemplate;

    public GetAddressApiClient(RestTemplateBuilder restTemplateBuilder,
                               ResponseHeaderInterceptor interceptor) {  // (1)
        restTemplate = restTemplateBuilder
                .rootUri("http://zipcloud.ibsnet.co.jp")
                .additionalInterceptors(interceptor)
                .build();
    }

    public GetAddressApiResponse request(String zipCode) {
        return restTemplate.getForObject("/api/search?zipcode={zipCode}",  // (2)
                GetAddressApiResponse.class,
                zipCode);
    }
}

@Component
public class ResponseHeaderInterceptor implements ClientHttpRequestInterceptor {

    @Override  // (3)
    public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution)
            throws IOException {
        ClientHttpResponse response = execution.execute(request, body);
        response.getHeaders().setContentType(MediaType.APPLICATION_JSON);
        return response;
    }

}