GH-3643: Defer MeterRegistry bean dependency

Fixes #3643

The `ImportBeanDefinitionRegistrar` register its bean definition in the early phase.
It causes a problem with Spring Boot when an explicit `@EnableIntegrationManagement`
is declared: the `MeterRegistry` is provided later on via auto-configuration
and `MicrometerMetricsCaptor` has no knowledge about `MeterRegistry` at the
`ImportBeanDefinitionRegistrar` phase.

* Reworks `MicrometerMetricsCaptorRegistrar` to the `MicrometerMetricsCaptorConfiguration`
and use special conditional `MicrometerMetricsCaptorImportSelector` for that
`@EnableIntegrationManagement`.
This way a `MicrometerMetricsCaptor` `@Bean` consults `ObjectProvider<MeterRegistry>`
on its creating time and returns `null` if no `MeterRegistry` beans at all.

Author: artembilan

spring-integration-core/src/main/java/org/springframework/integration/config/EnableIntegrationManagement.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2020 the original author or authors.
+ * Copyright 2014-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,7 +23,7 @@
 import java.lang.annotation.Target;
 
 import org.springframework.context.annotation.Import;
-import org.springframework.integration.support.management.micrometer.MicrometerMetricsCaptorRegistrar;
+import org.springframework.integration.support.management.micrometer.MicrometerMetricsCaptorImportSelector;
 
 /**
  * Enables default configuring of management in Spring Integration components in an existing application.
@@ -39,7 +39,7 @@
 @Target(ElementType.TYPE)
 @Retention(RetentionPolicy.RUNTIME)
 @Documented
-@Import({ MicrometerMetricsCaptorRegistrar.class, IntegrationManagementConfiguration.class })
+@Import({ MicrometerMetricsCaptorImportSelector.class, IntegrationManagementConfiguration.class })
 public @interface EnableIntegrationManagement {
 
 	/**

spring-integration-core/src/main/java/org/springframework/integration/graph/IntegrationGraphServer.java

@@ -48,7 +48,7 @@
 import org.springframework.integration.router.RecipientListRouterManagement;
 import org.springframework.integration.support.context.NamedComponent;
 import org.springframework.integration.support.management.MappingMessageRouterManagement;
-import org.springframework.integration.support.management.micrometer.MicrometerMetricsCaptorRegistrar;
+import org.springframework.integration.support.management.micrometer.MicrometerMetricsCaptorConfiguration;
 import org.springframework.integration.support.utils.IntegrationUtils;
 import org.springframework.lang.Nullable;
 import org.springframework.messaging.MessageChannel;
@@ -159,7 +159,7 @@ protected <T> Map<String, T> getBeansOfType(Class<T> type) {
 	}
 
 	private synchronized Graph buildGraph() {
-		if (micrometerEnhancer == null && MicrometerMetricsCaptorRegistrar.METER_REGISTRY_PRESENT) {
+		if (micrometerEnhancer == null && MicrometerMetricsCaptorConfiguration.METER_REGISTRY_PRESENT) {
 			micrometerEnhancer = new MicrometerNodeEnhancer(this.applicationContext);
 		}
 		String implementationVersion = IntegrationGraphServer.class.getPackage().getImplementationVersion();

spring-integration-core/src/main/java/org/springframework/integration/support/management/micrometer/MicrometerMetricsCaptorRegistrar.java renamed to spring-integration-core/src/main/java/org/springframework/integration/support/management/micrometer/MicrometerMetricsCaptorConfiguration.java

@@ -16,12 +16,10 @@
 
 package org.springframework.integration.support.management.micrometer;
 
-import org.springframework.beans.factory.ListableBeanFactory;
-import org.springframework.beans.factory.config.BeanDefinition;
-import org.springframework.beans.factory.support.BeanDefinitionBuilder;
-import org.springframework.beans.factory.support.BeanDefinitionRegistry;
+import org.springframework.beans.factory.ObjectProvider;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
-import org.springframework.core.type.AnnotationMetadata;
 import org.springframework.util.ClassUtils;
 
 import io.micrometer.core.instrument.MeterRegistry;
@@ -35,7 +33,8 @@
  *
  * @since 5.2.9
  */
-public class MicrometerMetricsCaptorRegistrar implements ImportBeanDefinitionRegistrar {
+@Configuration(proxyBeanMethods = false)
+public class MicrometerMetricsCaptorConfiguration {
 
 	/**
 	 * A {@code boolean} flag to indicate if the
@@ -45,18 +44,13 @@ public class MicrometerMetricsCaptorRegistrar implements ImportBeanDefinitionReg
 	public static final boolean METER_REGISTRY_PRESENT =
 			ClassUtils.isPresent("io.micrometer.core.instrument.MeterRegistry", null);
 
-	@Override
-	public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
-		ListableBeanFactory beanFactory = (ListableBeanFactory) registry;
-		if (METER_REGISTRY_PRESENT
-				&& !registry.containsBeanDefinition(MicrometerMetricsCaptor.MICROMETER_CAPTOR_NAME)
-				&& beanFactory.getBeanNamesForType(MeterRegistry.class, false, false).length > 0) {
-
-			registry.registerBeanDefinition(MicrometerMetricsCaptor.MICROMETER_CAPTOR_NAME,
-					BeanDefinitionBuilder.genericBeanDefinition(MicrometerMetricsCaptor.class,
-							() -> new MicrometerMetricsCaptor(beanFactory.getBeanProvider(MeterRegistry.class)))
-							.setRole(BeanDefinition.ROLE_INFRASTRUCTURE)
-							.getBeanDefinition());
+	@Bean(name = MicrometerMetricsCaptor.MICROMETER_CAPTOR_NAME)
+	public MicrometerMetricsCaptor micrometerMetricsCaptor(ObjectProvider<MeterRegistry> meterRegistries) {
+		if (meterRegistries.stream().findAny().isPresent()) {
+			return new MicrometerMetricsCaptor(meterRegistries);
+		}
+		else {
+			return null;
 		}
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/support/management/micrometer/MicrometerMetricsCaptorImportSelector.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.support.management.micrometer;
+
+import org.springframework.context.annotation.ImportSelector;
+import org.springframework.core.type.AnnotationMetadata;
+
+/**
+ * An {@link ImportSelector} to conditionally add a {@link MicrometerMetricsCaptorConfiguration}
+ * bean when {@code io.micrometer.core.instrument.MeterRegistry} is present in classpath.
+ *
+ * @author Artem Bilan
+ *
+ * @since 5.5.5
+ */
+public class MicrometerMetricsCaptorImportSelector implements ImportSelector {
+
+	@Override
+	public String[] selectImports(AnnotationMetadata importingClassMetadata) {
+		if (MicrometerMetricsCaptorConfiguration.METER_REGISTRY_PRESENT) {
+			return new String[]{ MicrometerMetricsCaptorConfiguration.class.getName() };
+		}
+		else {
+			return new String[0];
+		}
+	}
+
+}