Support virtual threading with JDK HTTP clients

Update JDK HTTP Clients so that the use virtual threads when
`Threading.VIRTUAL` is active.

See gh-46404

Signed-off-by: Sangmin Park <sangmins930@gmail.com>

module/spring-boot-http-client/src/main/java/org/springframework/boot/http/client/JdkClientHttpRequestFactoryBuilder.java

@@ -19,6 +19,7 @@ package org.springframework.boot.http.client;
 import java.net.http.HttpClient;
 import java.util.Collection;
 import java.util.List;
+import java.util.concurrent.Executors;
 import java.util.function.Consumer;
 
 import org.jspecify.annotations.Nullable;
@@ -75,6 +76,12 @@ public final class JdkClientHttpRequestFactoryBuilder
 				this.httpClientBuilder.withCustomizer(httpClientCustomizer));
 	}
 
+	public JdkClientHttpRequestFactoryBuilder enableVirtualThreadExecutor() {
+		return this.withHttpClientCustomizer(builder ->
+				builder.executor(Executors.newVirtualThreadPerTaskExecutor())
+		);
+	}
+
 	@Override
 	protected JdkClientHttpRequestFactory createClientHttpRequestFactory(ClientHttpRequestFactorySettings settings) {
 		HttpClient httpClient = this.httpClientBuilder.build(asHttpClientSettings(settings.withReadTimeout(null)));

module/spring-boot-http-client/src/main/java/org/springframework/boot/http/client/autoconfigure/HttpClientAutoConfiguration.java

@@ -24,10 +24,13 @@ 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.ConditionalOnMissingBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnThreading;
 import org.springframework.boot.autoconfigure.ssl.SslAutoConfiguration;
+import org.springframework.boot.autoconfigure.thread.Threading;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.boot.http.client.ClientHttpRequestFactoryBuilder;
 import org.springframework.boot.http.client.ClientHttpRequestFactorySettings;
+import org.springframework.boot.http.client.JdkClientHttpRequestFactoryBuilder;
 import org.springframework.boot.ssl.SslBundles;
 import org.springframework.boot.util.LambdaSafe;
 import org.springframework.context.annotation.Bean;
@@ -64,18 +67,31 @@ public final class HttpClientAutoConfiguration implements BeanClassLoaderAware {
 
 	@Bean
 	@ConditionalOnMissingBean
-	ClientHttpRequestFactoryBuilder<?> clientHttpRequestFactoryBuilder(
+	@ConditionalOnThreading(Threading.PLATFORM)
+	ClientHttpRequestFactoryBuilder<?> clientHttpRequestFactoryBuilderOnPlatform(
 			ObjectProvider<ClientHttpRequestFactoryBuilderCustomizer<?>> clientHttpRequestFactoryBuilderCustomizers) {
 		ClientHttpRequestFactoryBuilder<?> builder = this.factories.builder(this.beanClassLoader);
 		return customize(builder, clientHttpRequestFactoryBuilderCustomizers.orderedStream().toList());
 	}
 
+	@Bean
+	@ConditionalOnMissingBean
+	@ConditionalOnThreading(Threading.VIRTUAL)
+	ClientHttpRequestFactoryBuilder<?> clientHttpRequestFactoryBuilderOnVirtual(
+			ObjectProvider<ClientHttpRequestFactoryBuilderCustomizer<?>> clientHttpRequestFactoryBuilderCustomizers) {
+		ClientHttpRequestFactoryBuilder<?> builder = this.factories.builder(this.beanClassLoader);
+		if (builder instanceof JdkClientHttpRequestFactoryBuilder jdk) {
+			return customize(jdk.enableVirtualThreadExecutor(), clientHttpRequestFactoryBuilderCustomizers.orderedStream().toList());
+		}
+		return customize(builder, clientHttpRequestFactoryBuilderCustomizers.orderedStream().toList());
+	}
+
 	@SuppressWarnings("unchecked")
 	private ClientHttpRequestFactoryBuilder<?> customize(ClientHttpRequestFactoryBuilder<?> builder,
 			List<ClientHttpRequestFactoryBuilderCustomizer<?>> customizers) {
 		ClientHttpRequestFactoryBuilder<?>[] builderReference = { builder };
 		LambdaSafe.callbacks(ClientHttpRequestFactoryBuilderCustomizer.class, customizers, builderReference[0])
-			.invoke((customizer) -> builderReference[0] = customizer.customize(builderReference[0]));
+				.invoke((customizer) -> builderReference[0] = customizer.customize(builderReference[0]));
 		return builderReference[0];
 	}