Reverse the order of tracing and metrics handlers

Closes gh-32463

Co-authored-by: Jonatan Ivanov <jonatan.ivanov@gmail.com>

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/observation/TracingObservationHandlerGrouping.java

@@ -30,11 +30,10 @@ import io.micrometer.tracing.handler.TracingObservationHandler;
  * {@link ObservationHandlerGrouping} used by {@link ObservationAutoConfiguration} if
  * micrometer-tracing is on the classpath.
  *
- * Groups all {@link MeterObservationHandler} into a
+ * Groups all {@link TracingObservationHandler} into a
- * {@link FirstMatchingCompositeObservationHandler}, and all
+ * {@link FirstMatchingCompositeObservationHandler}, and {@link MeterObservationHandler}
- * {@link TracingObservationHandler} into a
+ * into a {@link FirstMatchingCompositeObservationHandler}. All other handlers are added
- * {@link FirstMatchingCompositeObservationHandler}. All other handlers are added to the
+ * to the {@link ObservationConfig} directly.
- * {@link ObservationConfig} directly.
  *
  * @author Moritz Halbritter
  */
@@ -45,22 +44,22 @@ class TracingObservationHandlerGrouping implements ObservationHandlerGrouping {
 		List<ObservationHandler<?>> meterObservationHandlers = new ArrayList<>();
 		List<ObservationHandler<?>> tracingObservationHandlers = new ArrayList<>();
 		for (ObservationHandler<?> handler : handlers) {
-			if (handler instanceof MeterObservationHandler<?>) {
+			if (handler instanceof TracingObservationHandler<?>) {
-				meterObservationHandlers.add(handler);
-			}
-			else if (handler instanceof TracingObservationHandler<?>) {
 				tracingObservationHandlers.add(handler);
 			}
+			else if (handler instanceof MeterObservationHandler<?>) {
+				meterObservationHandlers.add(handler);
+			}
 			else {
 				config.observationHandler(handler);
 			}
 		}
-		if (!meterObservationHandlers.isEmpty()) {
-			config.observationHandler(new FirstMatchingCompositeObservationHandler(meterObservationHandlers));
-		}
 		if (!tracingObservationHandlers.isEmpty()) {
 			config.observationHandler(new FirstMatchingCompositeObservationHandler(tracingObservationHandlers));
 		}
+		if (!meterObservationHandlers.isEmpty()) {
+			config.observationHandler(new FirstMatchingCompositeObservationHandler(meterObservationHandlers));
+		}
 	}
 
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/observation/ObservationAutoConfigurationTests.java

@@ -144,18 +144,18 @@ class ObservationAutoConfigurationTests {
 			assertThat(handlers).hasSize(3);
 			// Regular handlers are registered first
 			assertThat(handlers.get(0)).isInstanceOf(CustomObservationHandler.class);
-			// Multiple MeterObservationHandler are wrapped in
-			// FirstMatchingCompositeObservationHandler, which calls only the first
-			// one
-			assertThat(handlers.get(1)).isInstanceOf(CustomMeterObservationHandler.class);
-			assertThat(((CustomMeterObservationHandler) handlers.get(1)).getName())
-					.isEqualTo("customMeterObservationHandler1");
 			// Multiple TracingObservationHandler are wrapped in
 			// FirstMatchingCompositeObservationHandler, which calls only the first
 			// one
-			assertThat(handlers.get(2)).isInstanceOf(CustomTracingObservationHandler.class);
+			assertThat(handlers.get(1)).isInstanceOf(CustomTracingObservationHandler.class);
-			assertThat(((CustomTracingObservationHandler) handlers.get(2)).getName())
+			assertThat(((CustomTracingObservationHandler) handlers.get(1)).getName())
 					.isEqualTo("customTracingHandler1");
+			// Multiple MeterObservationHandler are wrapped in
+			// FirstMatchingCompositeObservationHandler, which calls only the first
+			// one
+			assertThat(handlers.get(2)).isInstanceOf(CustomMeterObservationHandler.class);
+			assertThat(((CustomMeterObservationHandler) handlers.get(2)).getName())
+					.isEqualTo("customMeterObservationHandler1");
 		});
 	}