Enable virtual threads on Tomcat

Closes gh-35704

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/web/reactive/ReactiveManagementChildContextConfiguration.java

@@ -28,6 +28,7 @@ import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplicat
 import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication.Type;
 import org.springframework.boot.autoconfigure.web.embedded.JettyWebServerFactoryCustomizer;
 import org.springframework.boot.autoconfigure.web.embedded.NettyWebServerFactoryCustomizer;
+import org.springframework.boot.autoconfigure.web.embedded.TomcatVirtualThreadsWebServerFactoryCustomizer;
 import org.springframework.boot.autoconfigure.web.embedded.TomcatWebServerFactoryCustomizer;
 import org.springframework.boot.autoconfigure.web.embedded.UndertowWebServerFactoryCustomizer;
 import org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryCustomizer;
@@ -76,7 +77,8 @@ public class ReactiveManagementChildContextConfiguration {
 
 		ReactiveManagementWebServerFactoryCustomizer(ListableBeanFactory beanFactory) {
 			super(beanFactory, ReactiveWebServerFactoryCustomizer.class, TomcatWebServerFactoryCustomizer.class,
-					TomcatReactiveWebServerFactoryCustomizer.class, JettyWebServerFactoryCustomizer.class,
+					TomcatReactiveWebServerFactoryCustomizer.class,
+					TomcatVirtualThreadsWebServerFactoryCustomizer.class, JettyWebServerFactoryCustomizer.class,
 					UndertowWebServerFactoryCustomizer.class, NettyWebServerFactoryCustomizer.class);
 		}
 

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/web/servlet/ServletManagementChildContextConfiguration.java

@@ -40,6 +40,7 @@ import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplicat
 import org.springframework.boot.autoconfigure.condition.SearchStrategy;
 import org.springframework.boot.autoconfigure.web.ServerProperties;
 import org.springframework.boot.autoconfigure.web.embedded.JettyWebServerFactoryCustomizer;
+import org.springframework.boot.autoconfigure.web.embedded.TomcatVirtualThreadsWebServerFactoryCustomizer;
 import org.springframework.boot.autoconfigure.web.embedded.TomcatWebServerFactoryCustomizer;
 import org.springframework.boot.autoconfigure.web.embedded.UndertowWebServerFactoryCustomizer;
 import org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryCustomizer;
@@ -122,8 +123,9 @@ class ServletManagementChildContextConfiguration {
 
 		ServletManagementWebServerFactoryCustomizer(ListableBeanFactory beanFactory) {
 			super(beanFactory, ServletWebServerFactoryCustomizer.class, TomcatServletWebServerFactoryCustomizer.class,
-					TomcatWebServerFactoryCustomizer.class, JettyWebServerFactoryCustomizer.class,
-					UndertowServletWebServerFactoryCustomizer.class, UndertowWebServerFactoryCustomizer.class);
+					TomcatWebServerFactoryCustomizer.class, TomcatVirtualThreadsWebServerFactoryCustomizer.class,
+					JettyWebServerFactoryCustomizer.class, UndertowServletWebServerFactoryCustomizer.class,
+					UndertowWebServerFactoryCustomizer.class);
 		}
 
 		@Override

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/embedded/EmbeddedWebServerFactoryCustomizerAutoConfiguration.java

@@ -29,6 +29,7 @@ import org.springframework.boot.autoconfigure.AutoConfiguration;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnNotWarDeployment;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnVirtualThreads;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
 import org.springframework.boot.autoconfigure.web.ServerProperties;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
@@ -62,6 +63,12 @@ public class EmbeddedWebServerFactoryCustomizerAutoConfiguration {
 			return new TomcatWebServerFactoryCustomizer(environment, serverProperties);
 		}
 
+		@Bean
+		@ConditionalOnVirtualThreads
+		TomcatVirtualThreadsWebServerFactoryCustomizer tomcatVirtualThreadsProtocolHandlerCustomizer() {
+			return new TomcatVirtualThreadsWebServerFactoryCustomizer();
+		}
+
 	}
 
 	/**

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/embedded/TomcatVirtualThreadsWebServerFactoryCustomizer.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.web.embedded;
+
+import org.apache.coyote.ProtocolHandler;
+import org.apache.tomcat.util.threads.VirtualThreadExecutor;
+
+import org.springframework.boot.web.embedded.tomcat.ConfigurableTomcatWebServerFactory;
+import org.springframework.boot.web.server.WebServerFactoryCustomizer;
+import org.springframework.core.Ordered;
+
+/**
+ * Activates {@link VirtualThreadExecutor} on {@link ProtocolHandler Tomcat's protocol
+ * handler}.
+ *
+ * @author Moritz Halbritter
+ * @since 3.2.0
+ */
+public class TomcatVirtualThreadsWebServerFactoryCustomizer
+		implements WebServerFactoryCustomizer<ConfigurableTomcatWebServerFactory>, Ordered {
+
+	@Override
+	public void customize(ConfigurableTomcatWebServerFactory factory) {
+		factory.addProtocolHandlerCustomizers(
+				(protocolHandler) -> protocolHandler.setExecutor(new VirtualThreadExecutor("tomcat-handler-")));
+	}
+
+	@Override
+	public int getOrder() {
+		return TomcatWebServerFactoryCustomizer.order + 1;
+	}
+
+}

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/embedded/TomcatWebServerFactoryCustomizer.java

@@ -67,6 +67,8 @@ import org.springframework.util.unit.DataSize;
 public class TomcatWebServerFactoryCustomizer
 		implements WebServerFactoryCustomizer<ConfigurableTomcatWebServerFactory>, Ordered {
 
+	static final int order = 0;
+
 	private final Environment environment;
 
 	private final ServerProperties serverProperties;
@@ -78,7 +80,7 @@ public class TomcatWebServerFactoryCustomizer
 
 	@Override
 	public int getOrder() {
-		return 0;
+		return order;
 	}
 
 	@Override

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/embedded/TomcatVirtualThreadsWebServerFactoryCustomizerTests.java

@@ -0,0 +1,64 @@
+/*
+ * 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.web.embedded;
+
+import java.util.function.Consumer;
+
+import org.apache.tomcat.util.threads.VirtualThreadExecutor;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.EnabledForJreRange;
+import org.junit.jupiter.api.condition.JRE;
+
+import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory;
+import org.springframework.boot.web.embedded.tomcat.TomcatWebServer;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link TomcatVirtualThreadsWebServerFactoryCustomizer}.
+ *
+ * @author Moritz Halbritter
+ */
+class TomcatVirtualThreadsWebServerFactoryCustomizerTests {
+
+	private final TomcatVirtualThreadsWebServerFactoryCustomizer customizer = new TomcatVirtualThreadsWebServerFactoryCustomizer();
+
+	@Test
+	@EnabledForJreRange(min = JRE.JAVA_21)
+	void shouldSetVirtualThreadExecutor() {
+		withWebServer((webServer) -> assertThat(webServer.getTomcat().getConnector().getProtocolHandler().getExecutor())
+			.isInstanceOf(VirtualThreadExecutor.class));
+	}
+
+	private TomcatWebServer getWebServer() {
+		TomcatServletWebServerFactory factory = new TomcatServletWebServerFactory(0);
+		this.customizer.customize(factory);
+		return (TomcatWebServer) factory.getWebServer();
+	}
+
+	private void withWebServer(Consumer<TomcatWebServer> callback) {
+		TomcatWebServer webServer = getWebServer();
+		webServer.start();
+		try {
+			callback.accept(webServer);
+		}
+		finally {
+			webServer.stop();
+		}
+	}
+
+}