Add customizer callback for WebHttpHandlerBuilder

Add a new interface for customizing the WebHttpHandlerBuilder before the HttpHandler is built from it.

See gh-39324

Author: BenchmarkingBuffalo

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * 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.
@@ -41,6 +41,7 @@
  *
  * @author Brian Clozel
  * @author Stephane Nicoll
+ * @author Lasse Wulff
  * @since 2.0.0
  */
 @AutoConfiguration(after = { WebFluxAutoConfiguration.class })
@@ -60,8 +61,11 @@ public AnnotationConfig(ApplicationContext applicationContext) {
 		}
 
 		@Bean
-		public HttpHandler httpHandler(ObjectProvider<WebFluxProperties> propsProvider) {
-			HttpHandler httpHandler = WebHttpHandlerBuilder.applicationContext(this.applicationContext).build();
+		public HttpHandler httpHandler(ObjectProvider<WebFluxProperties> propsProvider,
+				ObjectProvider<WebHttpHandlerBuilderCustomizer> handlerBuilderCustomizers) {
+			WebHttpHandlerBuilder handlerBuilder = WebHttpHandlerBuilder.applicationContext(this.applicationContext);
+			handlerBuilderCustomizers.orderedStream().forEach((customizer) -> customizer.customize(handlerBuilder));
+			HttpHandler httpHandler = handlerBuilder.build();
 			WebFluxProperties properties = propsProvider.getIfAvailable();
 			if (properties != null && StringUtils.hasText(properties.getBasePath())) {
 				Map<String, HttpHandler> handlersMap = Collections.singletonMap(properties.getBasePath(), httpHandler);

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

@@ -0,0 +1,36 @@
+/*
+ * 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.reactive;
+
+import org.springframework.web.server.adapter.WebHttpHandlerBuilder;
+
+/**
+ * Callback interface used to customize a {@link WebHttpHandlerBuilder}.
+ *
+ * @author Lasse Wulff
+ * @since 3.3.0
+ */
+@FunctionalInterface
+public interface WebHttpHandlerBuilderCustomizer {
+
+	/**
+	 * Callback to customize a {@link WebHttpHandlerBuilder} instance.
+	 * @param webHttpHandlerBuilder the handlerBuilder to customize
+	 */
+	void customize(WebHttpHandlerBuilder webHttpHandlerBuilder);
+
+}

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * 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.
@@ -23,8 +23,13 @@
 import org.springframework.boot.test.context.runner.ReactiveWebApplicationContextRunner;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.http.HttpStatus;
 import org.springframework.http.server.reactive.ContextPathCompositeHandler;
 import org.springframework.http.server.reactive.HttpHandler;
+import org.springframework.http.server.reactive.ServerHttpRequest;
+import org.springframework.http.server.reactive.ServerHttpResponse;
+import org.springframework.mock.http.server.reactive.MockServerHttpRequest;
+import org.springframework.mock.http.server.reactive.MockServerHttpResponse;
 import org.springframework.web.reactive.DispatcherHandler;
 import org.springframework.web.reactive.function.server.RouterFunction;
 import org.springframework.web.reactive.function.server.ServerResponse;
@@ -40,6 +45,7 @@
  * @author Brian Clozel
  * @author Stephane Nicoll
  * @author Andy Wilkinson
+ * @author Lasse Wulff
  */
 class HttpHandlerAutoConfigurationTests {
 
@@ -66,6 +72,20 @@ void shouldConfigureHttpHandlerWithoutWebFluxAutoConfiguration() {
 			.run((context) -> assertThat(context).hasSingleBean(HttpHandler.class));
 	}
 
+	@Test
+	void customizersAreCalled() {
+		this.contextRunner.withConfiguration(AutoConfigurations.of(WebFluxAutoConfiguration.class))
+			.withUserConfiguration(WebHttpHandlerBuilderCustomizers.class)
+			.run((context) -> {
+				assertThat(context).hasSingleBean(HttpHandler.class);
+				HttpHandler httpHandler = context.getBean(HttpHandler.class);
+				ServerHttpRequest request = MockServerHttpRequest.get("").build();
+				ServerHttpResponse response = new MockServerHttpResponse();
+				httpHandler.handle(request, response).block();
+				assertThat(response.getStatusCode()).isEqualTo(HttpStatus.I_AM_A_TEAPOT);
+			});
+	}
+
 	@Test
 	void shouldConfigureBasePathCompositeHandler() {
 		this.contextRunner.withConfiguration(AutoConfigurations.of(WebFluxAutoConfiguration.class))
@@ -104,4 +124,18 @@ WebHandler webHandler() {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class WebHttpHandlerBuilderCustomizers {
+
+		@Bean
+		WebHttpHandlerBuilderCustomizer customizerDecorator() {
+			return (webHttpHandlerBuilder) -> webHttpHandlerBuilder
+				.httpHandlerDecorator(((httpHandler) -> (request, response) -> {
+					response.setStatusCode(HttpStatus.I_AM_A_TEAPOT);
+					return response.setComplete();
+				}));
+		}
+
+	}
+
 }

spring-boot-project/spring-boot-docs/src/docs/asciidoc/web/reactive.adoc

@@ -44,6 +44,8 @@ The auto-configuration adds the following features on top of Spring's defaults:
 
 If you want to keep Spring Boot WebFlux features and you want to add additional {spring-framework-docs}/web/webflux/config.html[WebFlux configuration], you can add your own `@Configuration` class of type `WebFluxConfigurer` but *without* `@EnableWebFlux`.
 
+If you want to add additional customization to the auto-configured `HttpHandler`, you can define beans of type `WebHttpHandlerBuilderCustomizer` and use them to modify the `WebHttpHandlerBuilder`.
+
 If you want to take complete control of Spring WebFlux, you can add your own `@Configuration` annotated with `@EnableWebFlux`.