Implement @ConditionalOnVirtualThreads

Closes gh-35892

buildSrc/src/main/java/org/springframework/boot/build/context/properties/DocumentConfigurationProperties.java

@@ -106,6 +106,7 @@ public class DocumentConfigurationProperties extends DefaultTask {
 		config.accept("spring.reactor");
 		config.accept("spring.ssl");
 		config.accept("spring.task");
+		config.accept("spring.threads");
 		config.accept("spring.mandatory-file-encoding");
 		config.accept("info");
 		config.accept("spring.output.ansi.enabled");

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/condition/ConditionalOnVirtualThreads.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2012-2022 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.condition;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.springframework.boot.system.JavaVersion;
+import org.springframework.context.annotation.Conditional;
+
+/**
+ * {@link Conditional @Conditional} that only matches when virtual threads are available
+ * and enabled.
+ *
+ * @author Moritz Halbritter
+ * @since 3.2.0
+ */
+@Target({ ElementType.TYPE, ElementType.METHOD })
+@Retention(RetentionPolicy.RUNTIME)
+@Documented
+@ConditionalOnJava(JavaVersion.TWENTY_ONE)
+@ConditionalOnProperty(name = "spring.threads.virtual.enabled", havingValue = "true")
+public @interface ConditionalOnVirtualThreads {
+
+}

spring-boot-project/spring-boot-autoconfigure/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -2825,6 +2825,12 @@
       "name": "spring.sql.init.mode",
       "defaultValue": "embedded"
     },
+    {
+      "name": "spring.threads.virtual.enabled",
+      "type": "java.lang.Boolean",
+      "description": "Whether to use virtual threads.",
+      "defaultValue": false
+    },
     {
       "name": "spring.thymeleaf.prefix",
       "defaultValue": "classpath:/templates/"

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/condition/ConditionalOnVirtualThreadsTests.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2012-2019 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.condition;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.EnabledForJreRange;
+import org.junit.jupiter.api.condition.JRE;
+
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link ConditionalOnVirtualThreads @ConditionalOnVirtualThreads}.
+ *
+ * @author Moritz Halbritter
+ */
+class ConditionalOnVirtualThreadsTests {
+
+	private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
+		.withUserConfiguration(BasicConfiguration.class);
+
+	@Test
+	@EnabledForJreRange(max = JRE.JAVA_20)
+	void isDisabledOnJdkBelow21EvenIfPropertyIsSet() {
+		this.contextRunner.withPropertyValues("spring.threads.virtual.enabled=true")
+			.run((context) -> assertThat(context).doesNotHaveBean("someBean"));
+	}
+
+	@Test
+	@EnabledForJreRange(min = JRE.JAVA_21)
+	void isDisabledOnJdk21IfPropertyIsNotSet() {
+		this.contextRunner.run((context) -> assertThat(context).doesNotHaveBean("someBean"));
+	}
+
+	@Test
+	@EnabledForJreRange(min = JRE.JAVA_21)
+	void isEnabledOnJdk21IfPropertyIsSet() {
+		this.contextRunner.withPropertyValues("spring.threads.virtual.enabled=true")
+			.run((context) -> assertThat(context).hasBean("someBean"));
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class BasicConfiguration {
+
+		@Bean
+		@ConditionalOnVirtualThreads
+		String someBean() {
+			return "someBean";
+		}
+
+	}
+
+}