Add VirtualThreads bean and auto-configuration

This bean is only in the context if virtual threads are enabled. It can
be used to get access to the virtual thread executor.

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/thread/VirtualThreads.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2012-2023 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.boot.autoconfigure.thread;
+
+import java.lang.reflect.Method;
+import java.util.concurrent.Executor;
+import java.util.concurrent.Executors;
+
+import org.springframework.util.Assert;
+import org.springframework.util.ReflectionUtils;
+
+/**
+ * Virtual thread support.
+ *
+ * @author Moritz Halbritter
+ * @since 3.2.0
+ */
+public class VirtualThreads {
+
+	private final Executor executor;
+
+	VirtualThreads() {
+		Method method = ReflectionUtils.findMethod(Executors.class, "newVirtualThreadPerTaskExecutor");
+		Assert.notNull(method, "Executors.newVirtualThreadPerTaskExecutor() method is missing");
+		this.executor = (Executor) ReflectionUtils.invokeMethod(method, null);
+	}
+
+	/**
+	 * Returns the virtual thread executor.
+	 * @return the virtual thread executor
+	 */
+	public Executor getExecutor() {
+		return this.executor;
+	}
+
+}

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/thread/VirtualThreadsAutoConfiguration.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2012-2023 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.boot.autoconfigure.thread;
+
+import org.springframework.boot.autoconfigure.AutoConfiguration;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnVirtualThreads;
+import org.springframework.context.annotation.Bean;
+
+/**
+ * {@link EnableAutoConfiguration Auto-configuration} for virtual threads.
+ *
+ * @author Moritz Halbritter
+ * @since 3.2.0
+ */
+@AutoConfiguration
+@ConditionalOnVirtualThreads
+public class VirtualThreadsAutoConfiguration {
+
+	@Bean
+	VirtualThreads virtualThreads() {
+		return new VirtualThreads();
+	}
+
+}

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/thread/package-info.java

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-2023 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.
+ */
+
+/**
+ * Classes related to threads.
+ */
+package org.springframework.boot.autoconfigure.thread;

spring-boot-project/spring-boot-autoconfigure/src/main/resources/META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports

@@ -119,6 +119,7 @@ org.springframework.boot.autoconfigure.sql.init.SqlInitializationAutoConfigurati
 org.springframework.boot.autoconfigure.ssl.SslAutoConfiguration
 org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration
 org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration
+org.springframework.boot.autoconfigure.thread.VirtualThreadsAutoConfiguration
 org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration
 org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration
 org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/thread/VirtualThreadsAutoConfigurationTests.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2012-2023 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.boot.autoconfigure.thread;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.EnabledForJreRange;
+import org.junit.jupiter.api.condition.JRE;
+
+import org.springframework.boot.autoconfigure.AutoConfiguration;
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.context.annotation.ImportCandidates;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link VirtualThreadsAutoConfiguration}.
+ *
+ * @author Moritz Halbritter
+ */
+class VirtualThreadsAutoConfigurationTests {
+
+	private final ApplicationContextRunner runner = new ApplicationContextRunner()
+		.withConfiguration(AutoConfigurations.of(VirtualThreadsAutoConfiguration.class));
+
+	@Test
+	void shouldBeRegisteredInAutoConfigurationImports() {
+		assertThat(ImportCandidates.load(AutoConfiguration.class, null).getCandidates())
+			.contains(VirtualThreadsAutoConfiguration.class.getName());
+	}
+
+	@Test
+	@EnabledForJreRange(min = JRE.JAVA_21)
+	void shouldSupplyBeans() {
+		this.runner.withPropertyValues("spring.threads.virtual.enabled=true")
+			.run((context) -> assertThat(context).hasSingleBean(VirtualThreads.class));
+	}
+
+	@Test
+	@EnabledForJreRange(min = JRE.JAVA_21)
+	void shouldNotSupplyBeansIfVirtualThreadsAreNotEnabled() {
+		this.runner.withPropertyValues("spring.threads.virtual.enabled=false")
+			.run((context) -> assertThat(context).doesNotHaveBean(VirtualThreads.class));
+	}
+
+}

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/thread/VirtualThreadsTests.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2012-2023 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.boot.autoconfigure.thread;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.EnabledForJreRange;
+import org.junit.jupiter.api.condition.JRE;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+/**
+ * Tests for {@link VirtualThreads}.
+ *
+ * @author Moritz Halbritter
+ */
+class VirtualThreadsTests {
+
+	@Test
+	@EnabledForJreRange(max = JRE.JAVA_20)
+	void shouldThrowExceptionBelowJava21() {
+		assertThatThrownBy(VirtualThreads::new).isInstanceOf(IllegalArgumentException.class)
+			.hasMessage("Executors.newVirtualThreadPerTaskExecutor() method is missing");
+	}
+
+	@Test
+	@EnabledForJreRange(min = JRE.JAVA_21)
+	void shouldReturnExecutorOnJava21AndUp() {
+		VirtualThreads virtualThreads = new VirtualThreads();
+		assertThat(virtualThreads.getExecutor()).isNotNull();
+	}
+
+}