fix(openfeature): read OTEL_SERVICE_NAME for metrics resource (#11424)

fix(openfeature): read OTEL_SERVICE_NAME for metrics resource

Merge branch 'master' into sameerank/fix-flag-eval-metrics-service-name

Fix spotless formatting violations

Apply google-java-format to FlagEvalMetrics.java

Merge branch 'master' into sameerank/fix-flag-eval-metrics-service-name

Co-authored-by: devflow.devflow-routing-intake <devflow.devflow-routing-intake@kubernetes.us1.ddbuild.io>

Author: sameerank

products/feature-flagging/feature-flagging-api/src/main/java/datadog/trace/api/openfeature/FlagEvalMetrics.java

@@ -11,6 +11,7 @@
 import io.opentelemetry.sdk.metrics.SdkMeterProvider;
 import io.opentelemetry.sdk.metrics.export.AggregationTemporalitySelector;
 import io.opentelemetry.sdk.metrics.export.PeriodicMetricReader;
+import io.opentelemetry.sdk.resources.Resource;
 import java.io.Closeable;
 import java.time.Duration;
 import org.slf4j.Logger;
@@ -31,6 +32,10 @@ class FlagEvalMetrics implements Closeable {
   private static final String ENDPOINT_ENV = "OTEL_EXPORTER_OTLP_METRICS_ENDPOINT";
   // Generic env var fallback (base URL, /v1/metrics is appended)
   private static final String ENDPOINT_GENERIC_ENV = "OTEL_EXPORTER_OTLP_ENDPOINT";
+  // OTel standard env vars for service name
+  private static final String SERVICE_NAME_ENV = "OTEL_SERVICE_NAME";
+  private static final AttributeKey<String> SERVICE_NAME_KEY =
+      AttributeKey.stringKey("service.name");
 
   private static final AttributeKey<String> ATTR_FLAG_KEY =
       AttributeKey.stringKey("feature_flag.key");
@@ -68,8 +73,12 @@ class FlagEvalMetrics implements Closeable {
       PeriodicMetricReader reader =
           PeriodicMetricReader.builder(exporter).setInterval(EXPORT_INTERVAL).build();
 
+      // Build resource with service name from OTEL_SERVICE_NAME env var
+      // Resource.getDefault() only provides unknown_service:java, so we read env vars manually
+      Resource resource = buildResource();
+
       SdkMeterProvider sdkMeterProvider =
-          SdkMeterProvider.builder().registerMetricReader(reader).build();
+          SdkMeterProvider.builder().setResource(resource).registerMetricReader(reader).build();
       meterProvider = sdkMeterProvider;
 
       Meter meter = sdkMeterProvider.meterBuilder(METER_NAME).build();
@@ -83,9 +92,9 @@ class FlagEvalMetrics implements Closeable {
       log.debug("Flag evaluation metrics initialized, exporting to {}", endpoint);
     } catch (NoClassDefFoundError e) {
       log.error(
-          "OpenTelemetry SDK is not on the classpath — evaluation metrics disabled. "
-              + "Add opentelemetry-sdk-metrics and opentelemetry-exporter-otlp to your dependencies "
-              + "to enable flag evaluation metrics.",
+          "OpenTelemetry SDK is not on the classpath — evaluation metrics disabled. Add"
+              + " opentelemetry-sdk-metrics and opentelemetry-exporter-otlp to your dependencies to"
+              + " enable flag evaluation metrics.",
           e);
       counter = null;
       meterProvider = null;
@@ -154,4 +163,17 @@ void shutdown() {
       }
     }
   }
+
+  /**
+   * Builds a Resource with the service name from OTEL_SERVICE_NAME environment variable. Falls back
+   * to Resource.getDefault() if OTEL_SERVICE_NAME is not set.
+   */
+  private static Resource buildResource() {
+    String serviceName = ConfigHelper.env(SERVICE_NAME_ENV);
+    if (serviceName != null && !serviceName.isEmpty()) {
+      return Resource.getDefault()
+          .merge(Resource.builder().put(SERVICE_NAME_KEY, serviceName).build());
+    }
+    return Resource.getDefault();
+  }
 }