Add welcome page support for Spring WebFlux

This commit adds the support for static and templated welcome pages with
Spring WebFlux. The implementation is backed by a `RouterFunction`
that's serving a static `index.html` file or rendering an `index` view.

Closes gh-9785

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

@@ -31,6 +31,7 @@ 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.template.TemplateAvailabilityProviders;
 import org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration;
 import org.springframework.boot.autoconfigure.validation.ValidatorAdapter;
 import org.springframework.boot.autoconfigure.web.ConditionalOnEnabledResourceChain;
@@ -42,6 +43,7 @@ import org.springframework.boot.context.properties.EnableConfigurationProperties
 import org.springframework.boot.convert.ApplicationConversionService;
 import org.springframework.boot.web.codec.CodecCustomizer;
 import org.springframework.boot.web.reactive.filter.OrderedHiddenHttpMethodFilter;
+import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
@@ -59,6 +61,8 @@ import org.springframework.web.reactive.config.ResourceHandlerRegistry;
 import org.springframework.web.reactive.config.ViewResolverRegistry;
 import org.springframework.web.reactive.config.WebFluxConfigurationSupport;
 import org.springframework.web.reactive.config.WebFluxConfigurer;
+import org.springframework.web.reactive.function.server.RouterFunction;
+import org.springframework.web.reactive.function.server.ServerResponse;
 import org.springframework.web.reactive.result.method.HandlerMethodArgumentResolver;
 import org.springframework.web.reactive.result.method.annotation.ArgumentResolverConfigurer;
 import org.springframework.web.reactive.result.method.annotation.RequestMappingHandlerAdapter;
@@ -93,6 +97,20 @@ public class WebFluxAutoConfiguration {
 		return new OrderedHiddenHttpMethodFilter();
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	public static class WelcomePageConfiguration {
+
+		@Bean
+		public RouterFunction<ServerResponse> welcomePageRouterFunction(ApplicationContext applicationContext,
+				WebFluxProperties webFluxProperties, ResourceProperties resourceProperties) {
+			WelcomePageRouterFunctionFactory factory = new WelcomePageRouterFunctionFactory(
+					new TemplateAvailabilityProviders(applicationContext), applicationContext,
+					resourceProperties.getStaticLocations(), webFluxProperties.getStaticPathPattern());
+			return factory.createRouterFunction();
+		}
+
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	@EnableConfigurationProperties({ ResourceProperties.class, WebFluxProperties.class })
 	@Import({ EnableWebFluxConfiguration.class })

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

@@ -0,0 +1,90 @@
+/*
+ * Copyright 2012-2020 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 java.util.Arrays;
+
+import org.springframework.boot.autoconfigure.template.TemplateAvailabilityProviders;
+import org.springframework.context.ApplicationContext;
+import org.springframework.core.io.Resource;
+import org.springframework.core.io.ResourceLoader;
+import org.springframework.http.MediaType;
+import org.springframework.web.reactive.function.server.RouterFunction;
+import org.springframework.web.reactive.function.server.RouterFunctions;
+import org.springframework.web.reactive.function.server.ServerResponse;
+
+import static org.springframework.web.reactive.function.server.RequestPredicates.GET;
+import static org.springframework.web.reactive.function.server.RequestPredicates.accept;
+
+/**
+ * A {@link RouterFunction} factory for an application's welcome page. Supports both
+ * static and templated files. If both a static and templated index page are available,
+ * the static page is preferred.
+ *
+ * @author Brian Clozel
+ */
+final class WelcomePageRouterFunctionFactory {
+
+	private final String staticPathPattern;
+
+	private final Resource welcomePage;
+
+	private final boolean welcomePageTemplateExists;
+
+	WelcomePageRouterFunctionFactory(TemplateAvailabilityProviders templateAvailabilityProviders,
+			ApplicationContext applicationContext, String[] staticLocations, String staticPathPattern) {
+		this.staticPathPattern = staticPathPattern;
+		this.welcomePage = getWelcomePage(applicationContext, staticLocations);
+		this.welcomePageTemplateExists = welcomeTemplateExists(templateAvailabilityProviders, applicationContext);
+	}
+
+	private Resource getWelcomePage(ResourceLoader resourceLoader, String[] staticLocations) {
+		return Arrays.stream(staticLocations).map((location) -> getIndexHtml(resourceLoader, location))
+				.filter(this::isReadable).findFirst().orElse(null);
+	}
+
+	private Resource getIndexHtml(ResourceLoader resourceLoader, String location) {
+		return resourceLoader.getResource(location + "index.html");
+	}
+
+	private boolean isReadable(Resource resource) {
+		try {
+			return resource.exists() && (resource.getURL() != null);
+		}
+		catch (Exception ex) {
+			return false;
+		}
+	}
+
+	private boolean welcomeTemplateExists(TemplateAvailabilityProviders templateAvailabilityProviders,
+			ApplicationContext applicationContext) {
+		return templateAvailabilityProviders.getProvider("index", applicationContext) != null;
+	}
+
+	RouterFunction<ServerResponse> createRouterFunction() {
+		if (this.welcomePage != null && "/**".equals(this.staticPathPattern)) {
+			return RouterFunctions.route(GET("/").and(accept(MediaType.TEXT_HTML)),
+					(req) -> ServerResponse.ok().contentType(MediaType.TEXT_HTML).bodyValue(this.welcomePage));
+		}
+		else if (this.welcomePageTemplateExists) {
+			return RouterFunctions.route(GET("/").and(accept(MediaType.TEXT_HTML)),
+					(req) -> ServerResponse.ok().render("index"));
+		}
+		return null;
+	}
+
+}

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

@@ -0,0 +1,200 @@
+/*
+ * Copyright 2012-2020 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 java.nio.charset.StandardCharsets;
+import java.util.Collections;
+import java.util.Locale;
+import java.util.Map;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import reactor.core.publisher.Mono;
+
+import org.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider;
+import org.springframework.boot.autoconfigure.template.TemplateAvailabilityProviders;
+import org.springframework.context.support.StaticApplicationContext;
+import org.springframework.core.io.buffer.DataBuffer;
+import org.springframework.core.io.buffer.DataBufferFactory;
+import org.springframework.core.io.buffer.DefaultDataBufferFactory;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.MediaType;
+import org.springframework.test.web.reactive.server.WebTestClient;
+import org.springframework.web.reactive.function.server.HandlerStrategies;
+import org.springframework.web.reactive.result.view.View;
+import org.springframework.web.reactive.result.view.ViewResolver;
+import org.springframework.web.server.ServerWebExchange;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link WelcomePageRouterFunctionFactory}
+ *
+ * @author Brian Clozel
+ */
+class WelcomePageRouterFunctionFactoryTests {
+
+	private StaticApplicationContext applicationContext;
+
+	private final String[] noIndexLocations = { "classpath:/" };
+
+	private final String[] indexLocations = { "classpath:/public/", "classpath:/welcome-page/" };
+
+	@BeforeEach
+	void setup() {
+		this.applicationContext = new StaticApplicationContext();
+		this.applicationContext.refresh();
+	}
+
+	@Test
+	void handlesRequestForStaticPageThatAcceptsTextHtml() {
+		WebTestClient client = withStaticIndex();
+		client.get().uri("/").accept(MediaType.TEXT_HTML).exchange().expectStatus().isOk().expectBody(String.class)
+				.isEqualTo("welcome-page-static");
+	}
+
+	@Test
+	void handlesRequestForStaticPageThatAcceptsAll() {
+		WebTestClient client = withStaticIndex();
+		client.get().uri("/").accept(MediaType.ALL).exchange().expectStatus().isOk().expectBody(String.class)
+				.isEqualTo("welcome-page-static");
+	}
+
+	@Test
+	void doesNotHandleRequestThatDoesNotAcceptTextHtml() {
+		WebTestClient client = withStaticIndex();
+		client.get().uri("/").accept(MediaType.APPLICATION_JSON).exchange().expectStatus().isNotFound();
+	}
+
+	@Test
+	void handlesRequestWithNoAcceptHeader() {
+		WebTestClient client = withStaticIndex();
+		client.get().uri("/").exchange().expectStatus().isOk().expectBody(String.class)
+				.isEqualTo("welcome-page-static");
+	}
+
+	@Test
+	void handlesRequestWithEmptyAcceptHeader() {
+		WebTestClient client = withStaticIndex();
+		client.get().uri("/").header(HttpHeaders.ACCEPT, "").exchange().expectStatus().isOk().expectBody(String.class)
+				.isEqualTo("welcome-page-static");
+	}
+
+	@Test
+	void producesNotFoundResponseWhenThereIsNoWelcomePage() {
+		WelcomePageRouterFunctionFactory factory = factoryWithoutTemplateSupport(this.noIndexLocations, "/**");
+		assertThat(factory.createRouterFunction()).isNull();
+	}
+
+	@Test
+	void handlesRequestForTemplateThatAcceptsTextHtml() {
+		WebTestClient client = withTemplateIndex();
+		client.get().uri("/").accept(MediaType.TEXT_HTML).exchange().expectStatus().isOk().expectBody(String.class)
+				.isEqualTo("welcome-page-template");
+	}
+
+	@Test
+	void handlesRequestForTemplateThatAcceptsAll() {
+		WebTestClient client = withTemplateIndex();
+		client.get().uri("/").accept(MediaType.ALL).exchange().expectStatus().isOk().expectBody(String.class)
+				.isEqualTo("welcome-page-template");
+	}
+
+	@Test
+	void prefersAStaticResourceToATemplate() {
+		WebTestClient client = withStaticAndTemplateIndex();
+		client.get().uri("/").accept(MediaType.ALL).exchange().expectStatus().isOk().expectBody(String.class)
+				.isEqualTo("welcome-page-static");
+	}
+
+	private WebTestClient createClient(WelcomePageRouterFunctionFactory factory) {
+		return WebTestClient.bindToRouterFunction(factory.createRouterFunction()).build();
+	}
+
+	private WebTestClient createClient(WelcomePageRouterFunctionFactory factory, ViewResolver viewResolver) {
+		return WebTestClient.bindToRouterFunction(factory.createRouterFunction())
+				.handlerStrategies(HandlerStrategies.builder().viewResolver(viewResolver).build()).build();
+	}
+
+	private WebTestClient withStaticIndex() {
+		WelcomePageRouterFunctionFactory factory = factoryWithoutTemplateSupport(this.indexLocations, "/**");
+		return WebTestClient.bindToRouterFunction(factory.createRouterFunction()).build();
+	}
+
+	private WebTestClient withTemplateIndex() {
+		WelcomePageRouterFunctionFactory factory = factoryWithTemplateSupport(this.noIndexLocations);
+		TestViewResolver testViewResolver = new TestViewResolver();
+		return WebTestClient.bindToRouterFunction(factory.createRouterFunction())
+				.handlerStrategies(HandlerStrategies.builder().viewResolver(testViewResolver).build()).build();
+	}
+
+	private WebTestClient withStaticAndTemplateIndex() {
+		WelcomePageRouterFunctionFactory factory = factoryWithTemplateSupport(this.indexLocations);
+		TestViewResolver testViewResolver = new TestViewResolver();
+		return WebTestClient.bindToRouterFunction(factory.createRouterFunction())
+				.handlerStrategies(HandlerStrategies.builder().viewResolver(testViewResolver).build()).build();
+	}
+
+	private WelcomePageRouterFunctionFactory factoryWithoutTemplateSupport(String[] locations,
+			String staticPathPattern) {
+		return new WelcomePageRouterFunctionFactory(new TestTemplateAvailabilityProviders(), this.applicationContext,
+				locations, staticPathPattern);
+	}
+
+	private WelcomePageRouterFunctionFactory factoryWithTemplateSupport(String[] locations) {
+		return new WelcomePageRouterFunctionFactory(new TestTemplateAvailabilityProviders("index"),
+				this.applicationContext, locations, "/**");
+	}
+
+	static class TestTemplateAvailabilityProviders extends TemplateAvailabilityProviders {
+
+		TestTemplateAvailabilityProviders() {
+			super(Collections.emptyList());
+		}
+
+		TestTemplateAvailabilityProviders(String viewName) {
+			this((view, environment, classLoader, resourceLoader) -> view.equals(viewName));
+		}
+
+		TestTemplateAvailabilityProviders(TemplateAvailabilityProvider provider) {
+			super(Collections.singletonList(provider));
+		}
+
+	}
+
+	static class TestViewResolver implements ViewResolver {
+
+		@Override
+		public Mono<View> resolveViewName(String viewName, Locale locale) {
+			return Mono.just(new TestView());
+		}
+
+	}
+
+	static class TestView implements View {
+
+		private final DataBufferFactory bufferFactory = new DefaultDataBufferFactory();
+
+		@Override
+		public Mono<Void> render(Map<String, ?> model, MediaType contentType, ServerWebExchange exchange) {
+			DataBuffer buffer = this.bufferFactory.wrap("welcome-page-template".getBytes(StandardCharsets.UTF_8));
+			return exchange.getResponse().writeWith(Mono.just(buffer));
+		}
+
+	}
+
+}

spring-boot-project/spring-boot-autoconfigure/src/test/resources/welcome-page/index.html

@@ -1 +1 @@
-
+welcome-page-static

spring-boot-project/spring-boot-docs/src/docs/asciidoc/spring-boot-features.adoc

@@ -2796,6 +2796,14 @@ Any resources with a path in `+/webjars/**+` are served from jar files if they a
 TIP: Spring WebFlux applications do not strictly depend on the Servlet API, so they cannot be deployed as war files and do not use the `src/main/webapp` directory.
 
 
+[[boot-features-webflux-welcome-page]]
+==== Welcome Page
+Spring Boot supports both static and templated welcome pages.
+It first looks for an `index.html` file in the configured static content locations.
+If one is not found, it then looks for an `index` template.
+If either is found, it is automatically used as the welcome page of the application.
+
+
 
 [[boot-features-webflux-template-engines]]
 ==== Template Engines