Polishing.

Use existing constants.

See #4218

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/observability/ContextProviderFactory.java

@@ -31,6 +31,7 @@ import com.mongodb.reactivestreams.client.ReactiveContextProvider;
 
 import io.micrometer.observation.Observation;
 import io.micrometer.observation.ObservationRegistry;
+import io.micrometer.observation.contextpropagation.ObservationThreadLocalAccessor;
 import reactor.core.CoreSubscriber;
 
 /**
@@ -85,8 +86,7 @@ public class ContextProviderFactory {
 
 			Observation currentObservation = observationRegistry.getCurrentObservation();
 			if (currentObservation != null) {
-				// Aligned with ObservationThreadLocalAccessor.KEY
-				requestContext.put("micrometer.observation", currentObservation);
+				requestContext.put(ObservationThreadLocalAccessor.KEY, currentObservation);
 			}
 
 			return requestContext;

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/observability/MongoObservationCommandListener.java

@@ -29,6 +29,7 @@ import com.mongodb.event.CommandSucceededEvent;
 
 import io.micrometer.observation.Observation;
 import io.micrometer.observation.ObservationRegistry;
+import io.micrometer.observation.contextpropagation.ObservationThreadLocalAccessor;
 
 /**
  * Implement MongoDB's {@link CommandListener} using Micrometer's {@link Observation} API.
@@ -42,11 +43,6 @@ public class MongoObservationCommandListener implements CommandListener {
 
 	private static final Log log = LogFactory.getLog(MongoObservationCommandListener.class);
 
-	/**
-	 * Aligns with ObservationThreadLocalAccessor.KEY.
-	 */
-	private static final String MICROMETER_OBSERVATION_KEY = "micrometer.observation";
-
 	private final ObservationRegistry observationRegistry;
 	private final @Nullable ConnectionString connectionString;
 
@@ -119,7 +115,7 @@ public class MongoObservationCommandListener implements CommandListener {
 
 		observation.start();
 
-		requestContext.put(MICROMETER_OBSERVATION_KEY, observation);
+		requestContext.put(ObservationThreadLocalAccessor.KEY, observation);
 
 		if (log.isDebugEnabled()) {
 			log.debug(
@@ -136,7 +132,7 @@ public class MongoObservationCommandListener implements CommandListener {
 			return;
 		}
 
-		Observation observation = requestContext.getOrDefault(MICROMETER_OBSERVATION_KEY, null);
+		Observation observation = requestContext.getOrDefault(ObservationThreadLocalAccessor.KEY, null);
 		if (observation == null) {
 			return;
 		}
@@ -160,7 +156,7 @@ public class MongoObservationCommandListener implements CommandListener {
 			return;
 		}
 
-		Observation observation = requestContext.getOrDefault(MICROMETER_OBSERVATION_KEY, null);
+		Observation observation = requestContext.getOrDefault(ObservationThreadLocalAccessor.KEY, null);
 		if (observation == null) {
 			return;
 		}
@@ -185,7 +181,7 @@ public class MongoObservationCommandListener implements CommandListener {
 	@Nullable
 	private static Observation observationFromContext(RequestContext context) {
 
-		Observation observation = context.getOrDefault(MICROMETER_OBSERVATION_KEY, null);
+		Observation observation = context.getOrDefault(ObservationThreadLocalAccessor.KEY, null);
 
 		if (observation != null) {
 

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/observability/ReactiveIntegrationTests.java

@@ -73,7 +73,7 @@ public class ReactiveIntegrationTests extends SampleTestRunner {
 					.verifyComplete();
 
 			repository.findByLastname("Matthews") //
-					.contextWrite(Context.of("micrometer.observation", intermediate)) //
+					.contextWrite(Context.of(ObservationThreadLocalAccessor.KEY, intermediate)) //
 					.as(StepVerifier::create).assertNext(actual -> {
 
 						assertThat(actual).extracting("firstname", "lastname").containsExactly("Dave", "Matthews");