Send SMS from Spring Boot with the SendiMessage API

// application.properties:
//   sendimessage.key=${SENDIMESSAGE_KEY}
//   sendimessage.secret=${SENDIMESSAGE_SECRET}

@Service
public class MessageService {
    private final RestClient client;

    public MessageService(@Value("${sendimessage.key}") String apiKey,
                          @Value("${sendimessage.secret}") String apiSecret) {
        this.client = RestClient.builder()
            .baseUrl("https://api.sendimessage.com/v1")
            .defaultHeader("X-API-Key", apiKey)
            .defaultHeader("X-API-Secret", apiSecret)
            .build();
    }

    public Map<String, Object> send(String to, String content) {
        return client.post()
            .uri("/send-message")
            .contentType(MediaType.APPLICATION_JSON)
            .body(Map.of("number", to, "content", content))
            .retrieve()
            .onStatus(HttpStatusCode::isError, (req, res) -> {
                throw new IllegalStateException("SendiMessage error " + res.getStatusCode());
            })
            .body(new ParameterizedTypeReference<>() {}); // {message_handle=4e828182-…, status=QUEUED, …}
    }
}

@RestController
class SendiMessageWebhookController {
    @PostMapping("/webhooks/sendimessage")
    public ResponseEntity<Void> handle(@RequestBody Map<String, Object> event) {
        // Verify the SendiMessage-Signature header before trusting the event.
        return ResponseEntity.ok().build();
    }
}