Auto-configure VirtualThreadMetrics

See gh-43852

Signed-off-by: Dmytro Nosan <dimanosan@gmail.com>

spring-boot-project/spring-boot-actuator-autoconfigure/build.gradle

@@ -29,6 +29,7 @@ dependencies {
 	optional("io.lettuce:lettuce-core")
 	optional("io.micrometer:micrometer-observation")
 	optional("io.micrometer:micrometer-jakarta9")
+	optional("io.micrometer:micrometer-java21")
 	optional("io.micrometer:micrometer-tracing")
 	optional("io.micrometer:micrometer-tracing-bridge-brave")
 	optional("io.micrometer:micrometer-tracing-bridge-otel")

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/JvmMetricsAutoConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -16,6 +16,8 @@
 
 package org.springframework.boot.actuate.autoconfigure.metrics;
 
+import java.io.Closeable;
+
 import io.micrometer.core.instrument.MeterRegistry;
 import io.micrometer.core.instrument.binder.jvm.ClassLoaderMetrics;
 import io.micrometer.core.instrument.binder.jvm.JvmCompilationMetrics;
@@ -25,12 +27,21 @@ import io.micrometer.core.instrument.binder.jvm.JvmInfoMetrics;
 import io.micrometer.core.instrument.binder.jvm.JvmMemoryMetrics;
 import io.micrometer.core.instrument.binder.jvm.JvmThreadMetrics;
 
+import org.springframework.aot.hint.MemberCategory;
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.aot.hint.RuntimeHintsRegistrar;
+import org.springframework.beans.BeanUtils;
+import org.springframework.beans.factory.BeanClassLoaderAware;
+import org.springframework.beans.factory.DisposableBean;
+import org.springframework.beans.factory.FactoryBean;
 import org.springframework.boot.autoconfigure.AutoConfiguration;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.ImportRuntimeHints;
+import org.springframework.util.ClassUtils;
 
 /**
  * {@link EnableAutoConfiguration Auto-configuration} for JVM metrics.
@@ -44,6 +55,8 @@ import org.springframework.context.annotation.Bean;
 @ConditionalOnBean(MeterRegistry.class)
 public class JvmMetricsAutoConfiguration {
 
+	private static final String VIRTUAL_THREAD_METRICS_CLASS = "io.micrometer.java21.instrument.binder.jdk.VirtualThreadMetrics";
+
 	@Bean
 	@ConditionalOnMissingBean
 	public JvmGcMetrics jvmGcMetrics() {
@@ -86,4 +99,62 @@ public class JvmMetricsAutoConfiguration {
 		return new JvmCompilationMetrics();
 	}
 
+	@Bean
+	@ConditionalOnClass(name = VIRTUAL_THREAD_METRICS_CLASS)
+	@ConditionalOnMissingBean(type = VIRTUAL_THREAD_METRICS_CLASS)
+	@ImportRuntimeHints(VirtualThreadMetricsRuntimeHintsRegistrar.class)
+	VirtualThreadMetricsFactoryBean virtualThreadMetrics() {
+		return new VirtualThreadMetricsFactoryBean();
+	}
+
+	static final class VirtualThreadMetricsFactoryBean
+			implements FactoryBean<Object>, BeanClassLoaderAware, DisposableBean {
+
+		private ClassLoader classLoader;
+
+		private Class<?> instanceType;
+
+		private Object instance;
+
+		@Override
+		public void setBeanClassLoader(ClassLoader classLoader) {
+			this.classLoader = classLoader;
+		}
+
+		@Override
+		public Object getObject() {
+			if (this.instance == null) {
+				this.instance = BeanUtils.instantiateClass(getObjectType());
+			}
+			return this.instance;
+		}
+
+		@Override
+		public Class<?> getObjectType() {
+			if (this.instanceType == null) {
+				this.instanceType = ClassUtils.resolveClassName(VIRTUAL_THREAD_METRICS_CLASS, this.classLoader);
+			}
+			return this.instanceType;
+		}
+
+		@Override
+		public void destroy() throws Exception {
+			if (this.instance instanceof Closeable closeable) {
+				closeable.close();
+			}
+		}
+
+	}
+
+	static final class VirtualThreadMetricsRuntimeHintsRegistrar implements RuntimeHintsRegistrar {
+
+		@Override
+		public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+			hints.reflection()
+				.registerTypeIfPresent(classLoader, VIRTUAL_THREAD_METRICS_CLASS,
+						MemberCategory.INVOKE_PUBLIC_CONSTRUCTORS);
+		}
+
+	}
+
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/JvmMetricsAutoConfigurationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -16,6 +16,7 @@
 
 package org.springframework.boot.actuate.autoconfigure.metrics;
 
+import io.micrometer.core.instrument.binder.MeterBinder;
 import io.micrometer.core.instrument.binder.jvm.ClassLoaderMetrics;
 import io.micrometer.core.instrument.binder.jvm.JvmCompilationMetrics;
 import io.micrometer.core.instrument.binder.jvm.JvmGcMetrics;
@@ -24,7 +25,14 @@ import io.micrometer.core.instrument.binder.jvm.JvmInfoMetrics;
 import io.micrometer.core.instrument.binder.jvm.JvmMemoryMetrics;
 import io.micrometer.core.instrument.binder.jvm.JvmThreadMetrics;
 import org.junit.jupiter.api.Test;
-
+import org.junit.jupiter.api.condition.EnabledForJreRange;
+import org.junit.jupiter.api.condition.JRE;
+
+import org.springframework.aot.hint.MemberCategory;
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.aot.hint.TypeReference;
+import org.springframework.aot.hint.predicate.RuntimeHintsPredicates;
+import org.springframework.beans.BeanUtils;
 import org.springframework.boot.actuate.autoconfigure.metrics.test.MetricsRun;
 import org.springframework.boot.autoconfigure.AutoConfigurations;
 import org.springframework.boot.test.context.assertj.AssertableApplicationContext;
@@ -32,6 +40,7 @@ import org.springframework.boot.test.context.runner.ApplicationContextRunner;
 import org.springframework.boot.test.context.runner.ContextConsumer;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.util.ClassUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -95,6 +104,36 @@ class JvmMetricsAutoConfigurationTests {
 			.run(assertMetricsBeans().andThen((context) -> assertThat(context).hasBean("customJvmCompilationMetrics")));
 	}
 
+	@Test
+	@EnabledForJreRange(min = JRE.JAVA_21)
+	void autoConfiguresJvmMetricsWithVirtualThreadsMetrics() {
+		this.contextRunner.run(assertMetricsBeans()
+			.andThen((context) -> assertThat(context).hasSingleBean(getVirtualThreadMetricsClass())));
+	}
+
+	@Test
+	@EnabledForJreRange(min = JRE.JAVA_21)
+	void allowCustomVirtualThreadMetricsToBeUsed() {
+		Class<MeterBinder> virtualThreadMetricsClass = getVirtualThreadMetricsClass();
+		this.contextRunner
+			.withBean("customVirtualThreadMetrics", virtualThreadMetricsClass,
+					() -> BeanUtils.instantiateClass(virtualThreadMetricsClass))
+			.run(assertMetricsBeans()
+				.andThen((context) -> assertThat(context).hasSingleBean(getVirtualThreadMetricsClass())
+					.hasBean("customVirtualThreadMetrics")));
+	}
+
+	@Test
+	@EnabledForJreRange(min = JRE.JAVA_21)
+	void shouldRegisterVirtualThreadMetricsRuntimeHints() {
+		RuntimeHints hints = new RuntimeHints();
+		new JvmMetricsAutoConfiguration.VirtualThreadMetricsRuntimeHintsRegistrar().registerHints(hints,
+				getClass().getClassLoader());
+		assertThat(RuntimeHintsPredicates.reflection()
+			.onType(TypeReference.of(getVirtualThreadMetricsClass()))
+			.withMemberCategories(MemberCategory.INVOKE_PUBLIC_CONSTRUCTORS)).accepts(hints);
+	}
+
 	private ContextConsumer<AssertableApplicationContext> assertMetricsBeans() {
 		return (context) -> assertThat(context).hasSingleBean(JvmGcMetrics.class)
 			.hasSingleBean(JvmHeapPressureMetrics.class)
@@ -105,6 +144,12 @@ class JvmMetricsAutoConfigurationTests {
 			.hasSingleBean(JvmCompilationMetrics.class);
 	}
 
+	@SuppressWarnings("unchecked")
+	private static Class<MeterBinder> getVirtualThreadMetricsClass() {
+		return (Class<MeterBinder>) ClassUtils
+			.resolveClassName("io.micrometer.java21.instrument.binder.jdk.VirtualThreadMetrics", null);
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	static class CustomJvmGcMetricsConfiguration {