Add labels to counter callback examples

Author: jack-berg

doc-snippets/prometheus-migration/src/main/java/otel/OtelCounterCallback.java

@@ -1,19 +1,29 @@
 package otel;
 
 import io.opentelemetry.api.OpenTelemetry;
+import io.opentelemetry.api.common.AttributeKey;
+import io.opentelemetry.api.common.Attributes;
 import io.opentelemetry.api.metrics.Meter;
 
 public class OtelCounterCallback {
+  private static final AttributeKey<String> ZONE = AttributeKey.stringKey("zone");
+  private static final Attributes UPSTAIRS = Attributes.of(ZONE, "upstairs");
+  private static final Attributes DOWNSTAIRS = Attributes.of(ZONE, "downstairs");
+
   public static void counterCallbackUsage(OpenTelemetry openTelemetry) {
     Meter meter = openTelemetry.getMeter("smart.home");
-    // The smart energy meter maintains its own cumulative joule total in firmware.
-    // Use an asynchronous counter to report that value when a MetricReader
-    // collects metrics, without maintaining a separate counter in application code.
+    // Each zone has its own smart energy meter tracking cumulative joule totals.
+    // Use an asynchronous counter to report those values when a MetricReader
+    // collects metrics, without maintaining separate counters in application code.
     meter
         .counterBuilder("energy.consumed")
         .setDescription("Total energy consumed")
         .setUnit("J")
         .ofDoubles()
-        .buildWithCallback(measurement -> measurement.record(SmartHomeDevices.totalEnergyJoules()));
+        .buildWithCallback(
+            measurement -> {
+              measurement.record(SmartHomeDevices.totalEnergyJoules("upstairs"), UPSTAIRS);
+              measurement.record(SmartHomeDevices.totalEnergyJoules("downstairs"), DOWNSTAIRS);
+            });
   }
 }

doc-snippets/prometheus-migration/src/main/java/otel/PrometheusCounterCallback.java

@@ -4,13 +4,18 @@
 
 public class PrometheusCounterCallback {
   public static void counterCallbackUsage() {
-    // The smart energy meter maintains its own cumulative joule total in firmware.
-    // Use a callback counter to report that value at scrape time without
-    // maintaining a separate counter in application code.
+    // Each zone has its own smart energy meter tracking cumulative joule totals.
+    // Use a callback counter to report those values at scrape time without
+    // maintaining separate counters in application code.
     CounterWithCallback.builder()
         .name("energy_consumed_joules_total")
         .help("Total energy consumed in joules")
-        .callback(callback -> callback.call(SmartHomeDevices.totalEnergyJoules()))
+        .labelNames("zone")
+        .callback(
+            callback -> {
+              callback.call(SmartHomeDevices.totalEnergyJoules("upstairs"), "upstairs");
+              callback.call(SmartHomeDevices.totalEnergyJoules("downstairs"), "downstairs");
+            })
         .register();
   }
 }

doc-snippets/prometheus-migration/src/main/java/otel/SmartHomeDevices.java

@@ -3,10 +3,10 @@
 /** Stubs representing smart home device APIs. */
 class SmartHomeDevices {
   /**
-   * Returns cumulative energy consumed in joules since installation, as reported by the smart
-   * energy meter device.
+   * Returns cumulative energy consumed in joules since installation in the given zone, as reported
+   * by the smart energy meter device.
    */
-  static double totalEnergyJoules() {
+  static double totalEnergyJoules(String zone) {
     return 0.0; // In production, this would query the device API.
   }