Reapply "Configure virtual threads on Undertow if enabled"

This reverts commit 2f99c19f11.

Closes gh-38819

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

@@ -34,15 +34,18 @@ import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplicat
 import org.springframework.boot.autoconfigure.thread.Threading;
 import org.springframework.boot.autoconfigure.web.ServerProperties;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.boot.web.embedded.undertow.UndertowDeploymentInfoCustomizer;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.env.Environment;
+import org.springframework.core.task.VirtualThreadTaskExecutor;
 
 /**
  * {@link EnableAutoConfiguration Auto-configuration} for embedded servlet and reactive
  * web servers customizations.
  *
  * @author Phillip Webb
+ * @author Moritz Halbritter
  * @since 2.0.0
  */
 @AutoConfiguration
@@ -107,6 +110,12 @@ public class EmbeddedWebServerFactoryCustomizerAutoConfiguration {
 			return new UndertowWebServerFactoryCustomizer(environment, serverProperties);
 		}
 
+		@Bean
+		@ConditionalOnThreading(Threading.VIRTUAL)
+		UndertowDeploymentInfoCustomizer virtualThreadsUndertowDeploymentInfoCustomizer() {
+			return (deploymentInfo) -> deploymentInfo.setExecutor(new VirtualThreadTaskExecutor("undertow-"));
+		}
+
 	}
 
 	/**

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

@@ -77,8 +77,7 @@ public class UndertowWebServerFactoryCustomizer
 	public void customize(ConfigurableUndertowWebServerFactory factory) {
 		PropertyMapper map = PropertyMapper.get().alwaysApplyingWhenNonNull();
 		ServerOptions options = new ServerOptions(factory);
-		ServerProperties properties = this.serverProperties;
-		map.from(properties::getMaxHttpRequestHeaderSize)
+		map.from(this.serverProperties::getMaxHttpRequestHeaderSize)
 			.asInt(DataSize::toBytes)
 			.when(this::isPositive)
 			.to(options.option(UndertowOptions.MAX_HEADER_SIZE));

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

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2012-2024 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 io.undertow.servlet.api.DeploymentInfo;
+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.AutoConfigurations;
+import org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration.UndertowWebServerFactoryCustomizerConfiguration;
+import org.springframework.boot.test.context.runner.WebApplicationContextRunner;
+import org.springframework.boot.web.embedded.undertow.UndertowDeploymentInfoCustomizer;
+import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebApplicationContext;
+import org.springframework.core.task.VirtualThreadTaskExecutor;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link UndertowWebServerFactoryCustomizerConfiguration}.
+ *
+ * @author Moritz Halbritter
+ */
+class UndertowWebServerFactoryCustomizerConfigurationTests {
+
+	private final WebApplicationContextRunner contextRunner = new WebApplicationContextRunner(
+			AnnotationConfigServletWebApplicationContext::new)
+		.withConfiguration(AutoConfigurations.of(EmbeddedWebServerFactoryCustomizerAutoConfiguration.class));
+
+	@EnabledForJreRange(min = JRE.JAVA_21)
+	@Test
+	void shouldUseVirtualThreadsIfEnabled() {
+		this.contextRunner.withPropertyValues("spring.threads.virtual.enabled=true").run((context) -> {
+			assertThat(context).hasSingleBean(UndertowDeploymentInfoCustomizer.class);
+			assertThat(context).hasBean("virtualThreadsUndertowDeploymentInfoCustomizer");
+			UndertowDeploymentInfoCustomizer customizer = context.getBean(UndertowDeploymentInfoCustomizer.class);
+			DeploymentInfo deploymentInfo = new DeploymentInfo();
+			customizer.customize(deploymentInfo);
+			assertThat(deploymentInfo.getExecutor()).isInstanceOf(VirtualThreadTaskExecutor.class);
+		});
+	}
+
+}