Configure WebFlux's blocking execution to use applicationTaskExecutor

Closes gh-36331

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/reactive/WebFluxAutoConfiguration.java

@@ -32,6 +32,7 @@ import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
 import org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration;
+import org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration;
 import org.springframework.boot.autoconfigure.template.TemplateAvailabilityProviders;
 import org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration;
 import org.springframework.boot.autoconfigure.validation.ValidatorAdapter;
@@ -54,12 +55,14 @@ import org.springframework.context.annotation.Import;
 import org.springframework.context.annotation.ImportRuntimeHints;
 import org.springframework.core.Ordered;
 import org.springframework.core.annotation.Order;
+import org.springframework.core.task.AsyncTaskExecutor;
 import org.springframework.format.FormatterRegistry;
 import org.springframework.format.support.FormattingConversionService;
 import org.springframework.http.codec.ServerCodecConfigurer;
 import org.springframework.util.ClassUtils;
 import org.springframework.validation.Validator;
 import org.springframework.web.filter.reactive.HiddenHttpMethodFilter;
+import org.springframework.web.reactive.config.BlockingExecutionConfigurer;
 import org.springframework.web.reactive.config.DelegatingWebFluxConfiguration;
 import org.springframework.web.reactive.config.EnableWebFlux;
 import org.springframework.web.reactive.config.ResourceHandlerRegistration;
@@ -184,6 +187,17 @@ public class WebFluxAutoConfiguration {
 			this.codecCustomizers.orderedStream().forEach((customizer) -> customizer.customize(configurer));
 		}
 
+		@Override
+		public void configureBlockingExecution(BlockingExecutionConfigurer configurer) {
+			if (this.beanFactory.containsBean(TaskExecutionAutoConfiguration.APPLICATION_TASK_EXECUTOR_BEAN_NAME)) {
+				Object taskExecutor = this.beanFactory
+					.getBean(TaskExecutionAutoConfiguration.APPLICATION_TASK_EXECUTOR_BEAN_NAME);
+				if (taskExecutor instanceof AsyncTaskExecutor asyncTaskExecutor) {
+					configurer.setExecutor(asyncTaskExecutor);
+				}
+			}
+		}
+
 		@Override
 		public void addResourceHandlers(ResourceHandlerRegistry registry) {
 			if (!this.resourceProperties.isAddMappings()) {

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/reactive/WebFluxAutoConfigurationTests.java

@@ -28,6 +28,7 @@ import java.util.Date;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.concurrent.Executor;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Consumer;
 
@@ -43,6 +44,7 @@ import org.junit.jupiter.params.provider.ValueSource;
 import org.springframework.aop.support.AopUtils;
 import org.springframework.boot.autoconfigure.AutoConfigurations;
 import org.springframework.boot.autoconfigure.aop.AopAutoConfiguration;
+import org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration;
 import org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration;
 import org.springframework.boot.autoconfigure.validation.ValidatorAdapter;
 import org.springframework.boot.autoconfigure.web.ServerProperties;
@@ -62,6 +64,7 @@ import org.springframework.core.Ordered;
 import org.springframework.core.annotation.Order;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.task.AsyncTaskExecutor;
 import org.springframework.format.Parser;
 import org.springframework.format.Printer;
 import org.springframework.format.support.FormattingConversionService;
@@ -79,6 +82,7 @@ import org.springframework.web.bind.annotation.ControllerAdvice;
 import org.springframework.web.filter.reactive.HiddenHttpMethodFilter;
 import org.springframework.web.reactive.HandlerMapping;
 import org.springframework.web.reactive.accept.RequestedContentTypeResolver;
+import org.springframework.web.reactive.config.BlockingExecutionConfigurer;
 import org.springframework.web.reactive.config.DelegatingWebFluxConfiguration;
 import org.springframework.web.reactive.config.WebFluxConfigurationSupport;
 import org.springframework.web.reactive.config.WebFluxConfigurer;
@@ -667,6 +671,47 @@ class WebFluxAutoConfigurationTests {
 				.hasSingleBean(CustomExceptionHandler.class));
 	}
 
+	@Test
+	void asyncTaskExecutorWithApplicationTaskExecutor() {
+		this.contextRunner.withConfiguration(AutoConfigurations.of(TaskExecutionAutoConfiguration.class))
+			.run((context) -> {
+				assertThat(context).hasSingleBean(AsyncTaskExecutor.class);
+				assertThat(context.getBean(RequestMappingHandlerAdapter.class)).extracting("scheduler.executor")
+					.isSameAs(context.getBean("applicationTaskExecutor"));
+			});
+	}
+
+	@Test
+	void asyncTaskExecutorWithNonMatchApplicationTaskExecutorBean() {
+		this.contextRunner.withUserConfiguration(CustomApplicationTaskExecutorConfig.class)
+			.withConfiguration(AutoConfigurations.of(TaskExecutionAutoConfiguration.class))
+			.run((context) -> {
+				assertThat(context).doesNotHaveBean(AsyncTaskExecutor.class);
+				assertThat(context.getBean(RequestMappingHandlerAdapter.class)).extracting("scheduler.executor")
+					.isNotSameAs(context.getBean("applicationTaskExecutor"));
+			});
+	}
+
+	@Test
+	void asyncTaskExecutorWithWebFluxConfigurerCanOverrideExecutor() {
+		this.contextRunner.withUserConfiguration(CustomAsyncTaskExecutorConfigurer.class)
+			.withConfiguration(AutoConfigurations.of(TaskExecutionAutoConfiguration.class))
+			.run((context) -> assertThat(context.getBean(RequestMappingHandlerAdapter.class))
+				.extracting("scheduler.executor")
+				.isSameAs(context.getBean(CustomAsyncTaskExecutorConfigurer.class).taskExecutor));
+	}
+
+	@Test
+	void asyncTaskExecutorWithCustomNonApplicationTaskExecutor() {
+		this.contextRunner.withUserConfiguration(CustomAsyncTaskExecutorConfig.class)
+			.withConfiguration(AutoConfigurations.of(TaskExecutionAutoConfiguration.class))
+			.run((context) -> {
+				assertThat(context).hasSingleBean(AsyncTaskExecutor.class);
+				assertThat(context.getBean(RequestMappingHandlerAdapter.class)).extracting("scheduler.executor")
+					.isNotSameAs(context.getBean("customTaskExecutor"));
+			});
+	}
+
 	private ContextConsumer<ReactiveWebApplicationContext> assertExchangeWithSession(
 			Consumer<MockServerWebExchange> exchange) {
 		return (context) -> {
@@ -981,4 +1026,36 @@ class WebFluxAutoConfigurationTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class CustomApplicationTaskExecutorConfig {
+
+		@Bean
+		Executor applicationTaskExecutor() {
+			return mock(Executor.class);
+		}
+
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class CustomAsyncTaskExecutorConfig {
+
+		@Bean
+		AsyncTaskExecutor customTaskExecutor() {
+			return mock(AsyncTaskExecutor.class);
+		}
+
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class CustomAsyncTaskExecutorConfigurer implements WebFluxConfigurer {
+
+		private final AsyncTaskExecutor taskExecutor = mock(AsyncTaskExecutor.class);
+
+		@Override
+		public void configureBlockingExecution(BlockingExecutionConfigurer configurer) {
+			configurer.setExecutor(this.taskExecutor);
+		}
+
+	}
+
 }

spring-boot-project/spring-boot-docs/src/docs/asciidoc/features/task-execution-and-scheduling.adoc

@@ -3,12 +3,12 @@
 In the absence of an `Executor` bean in the context, Spring Boot auto-configures an `AsyncTaskExecutor`.
 When virtual threads are enabled (using Java 21+ and configprop:spring.threads.virtual.enabled[] set to `true`) this will be a `SimpleAsyncTaskExecutor` that uses virtual threads.
 Otherwise, it will be a `ThreadPoolTaskExecutor` with sensible defaults.
-In either case, the auto-configured executor will be automatically used for asynchronous task execution (`@EnableAsync`) and Spring MVC asynchronous request processing.
+In either case, the auto-configured executor will be automatically used for asynchronous task execution (`@EnableAsync`), Spring MVC asynchronous request processing, and Spring WebFlux blocking execution.
 
 [TIP]
 ====
-If you have defined a custom `Executor` in the context, regular task execution (that is `@EnableAsync`) will use it transparently but the Spring MVC support will not be configured as it requires an `AsyncTaskExecutor` implementation (named `applicationTaskExecutor`).
-Depending on your target arrangement, you could change your `Executor` into a `ThreadPoolTaskExecutor` or define both a `ThreadPoolTaskExecutor` and an `AsyncConfigurer` wrapping your custom `Executor`.
+If you have defined a custom `Executor` in the context, regular task execution (that is `@EnableAsync`) will use it transparently but the Spring MVC and Spring WebFlux support will not be configured as they require an `AsyncTaskExecutor` implementation (named `applicationTaskExecutor`).
+Depending on your target arrangement, you could change your `Executor` into an `AsyncTaskExecutor` or define both an `AsyncTaskExecutor` and an `AsyncConfigurer` wrapping your custom `Executor`.
 
 The auto-configured `TaskExecutorBuilder` allows you to easily create instances that reproduce what the auto-configuration does by default.
 ====