Java Feature Flags

3. Evaluate flags

import okhttp3.*;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.cache.annotation.Cacheable;
import java.util.Map;

@Service
public class FlagBitService {
    private final OkHttpClient client = new OkHttpClient();
    private final ObjectMapper mapper = new ObjectMapper();

    @Value("${flagbit.sdk-key}")
    private String sdkKey;

    @Cacheable(value = "flags", key = "#flagKey + #context.hashCode()")
    public boolean isEnabled(String flagKey, Map<String, String> context) {
        try {
            String body = mapper.writeValueAsString(Map.of(
                "flag_key", flagKey,
                "context", context != null ? context : Map.of()
            ));
            Request request = new Request.Builder()
                .url("https://flagbit.anethoth.com/api/v1/evaluate")
                .addHeader("X-SDK-Key", sdkKey)
                .addHeader("Content-Type", "application/json")
                .post(RequestBody.create(body, MediaType.parse("application/json")))
                .build();
            Response resp = client.newCall(request).execute();
            var result = mapper.readTree(resp.body().string());
            return result.get("value").asBoolean();
        } catch (Exception e) {
            return false;
        }
    }
}

// Custom annotation
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface FeatureFlag {
    String value();
}

// AOP aspect
@Aspect
@Component
public class FeatureFlagAspect {
    @Autowired private FlagBitService flagBit;

    @Around("@annotation(flag)")
    public Object checkFlag(ProceedingJoinPoint jp, FeatureFlag flag) throws Throwable {
        if (flagBit.isEnabled(flag.value(), Map.of())) {
            return jp.proceed();
        }
        throw new ResponseStatusException(HttpStatus.NOT_FOUND);
    }
}

// Controller usage
@RestController
public class DashboardController {
    @FeatureFlag("new-analytics")
    @GetMapping("/api/analytics/v2")
    public ResponseEntity<?> newAnalytics() {
        return ResponseEntity.ok(analyticsService.getV2Data());
    }
}