Allow DefaultMeterObservationHandler to be replaced by user's bean

Closes gh-32462

Co-authored-by: Jonatan Ivanov <[email protected]>

Author: wilkinsona

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

@@ -17,6 +17,8 @@
 package org.springframework.boot.actuate.autoconfigure.observation;
 
 import io.micrometer.core.instrument.MeterRegistry;
+import io.micrometer.core.instrument.observation.DefaultMeterObservationHandler;
+import io.micrometer.core.instrument.observation.MeterObservationHandler;
 import io.micrometer.observation.GlobalObservationConvention;
 import io.micrometer.observation.ObservationHandler;
 import io.micrometer.observation.ObservationPredicate;
@@ -66,9 +68,9 @@ ObservationRegistry observationRegistry() {
 	static class MetricsConfiguration {
 
 		@Bean
-		DefaultMeterObservationHandlerObservationRegistryCustomizer enableDefaultMeterObservationHandler(
-				MeterRegistry meterRegistry) {
-			return new DefaultMeterObservationHandlerObservationRegistryCustomizer(meterRegistry);
+		@ConditionalOnMissingBean(MeterObservationHandler.class)
+		DefaultMeterObservationHandler defaultMeterObservationHandler(MeterRegistry meterRegistry) {
+			return new DefaultMeterObservationHandler(meterRegistry);
 		}
 
 	}

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

@@ -22,6 +22,7 @@
 import io.micrometer.common.KeyValue;
 import io.micrometer.common.KeyValues;
 import io.micrometer.core.instrument.MeterRegistry;
+import io.micrometer.core.instrument.observation.DefaultMeterObservationHandler;
 import io.micrometer.core.instrument.observation.MeterObservationHandler;
 import io.micrometer.core.instrument.search.MeterNotFoundException;
 import io.micrometer.observation.GlobalObservationConvention;
@@ -67,6 +68,7 @@ class ObservationAutoConfigurationTests {
 	@Test
 	void autoConfiguresDefaultMeterObservationHandler() {
 		this.contextRunner.run((context) -> {
+			assertThat(context).hasSingleBean(DefaultMeterObservationHandler.class);
 			ObservationRegistry observationRegistry = context.getBean(ObservationRegistry.class);
 			Observation.start("test-observation", observationRegistry).stop();
 			// When a DefaultMeterObservationHandler is registered, every stopped
@@ -76,13 +78,6 @@ void autoConfiguresDefaultMeterObservationHandler() {
 		});
 	}
 
-	@Test
-	void allowsDefaultMeterObservationHandlerToBeDisabled() {
-		this.contextRunner.withClassLoader(new FilteredClassLoader(MeterRegistry.class))
-				.run((context) -> assertThat(context)
-						.doesNotHaveBean(DefaultMeterObservationHandlerObservationRegistryCustomizer.class));
-	}
-
 	@Test
 	void autoConfiguresObservationPredicates() {
 		this.contextRunner.withUserConfiguration(ObservationPredicates.class).run((context) -> {
@@ -109,11 +104,12 @@ void autoConfiguresGlobalKeyValuesProvider() {
 	}
 
 	@Test
-	void autoConfiguresObservationHandler() {
+	void autoConfiguresObservationHandlers() {
 		this.contextRunner.withUserConfiguration(ObservationHandlers.class).run((context) -> {
 			ObservationRegistry observationRegistry = context.getBean(ObservationRegistry.class);
 			List<ObservationHandler<?>> handlers = context.getBean(CalledHandlers.class).getCalledHandlers();
 			Observation.start("test-observation", observationRegistry);
+			assertThat(context).doesNotHaveBean(DefaultMeterObservationHandler.class);
 			assertThat(handlers).hasSize(2);
 			// Regular handlers are registered first
 			assertThat(handlers.get(0)).isInstanceOf(CustomObservationHandler.class);