Add and adapt reactive health contributors

Update `HealthEndpointConfiguration` to also include adapted reactive
health contributors when project reactor is on the classpath. Prior to
this commit, reactive contributors were only exposed in WebFlux
applications. This was a regression from Spring Boot 2.1 that we didn't
catch because all our own reactive contributors all have non-reactive
equivalents.

Closes gh-18805

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/health/HealthEndpointConfiguration.java

@@ -16,13 +16,23 @@
 
 package org.springframework.boot.actuate.autoconfigure.health;
 
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.LinkedHashMap;
 import java.util.Map;
 
+import org.springframework.boot.actuate.health.CompositeHealthContributor;
+import org.springframework.boot.actuate.health.CompositeReactiveHealthContributor;
+import org.springframework.boot.actuate.health.Health;
 import org.springframework.boot.actuate.health.HealthContributor;
 import org.springframework.boot.actuate.health.HealthContributorRegistry;
 import org.springframework.boot.actuate.health.HealthEndpoint;
 import org.springframework.boot.actuate.health.HealthEndpointGroups;
+import org.springframework.boot.actuate.health.HealthIndicator;
 import org.springframework.boot.actuate.health.HttpCodeStatusMapper;
+import org.springframework.boot.actuate.health.NamedContributor;
+import org.springframework.boot.actuate.health.ReactiveHealthContributor;
+import org.springframework.boot.actuate.health.ReactiveHealthIndicator;
 import org.springframework.boot.actuate.health.SimpleHttpCodeStatusMapper;
 import org.springframework.boot.actuate.health.SimpleStatusAggregator;
 import org.springframework.boot.actuate.health.StatusAggregator;
@@ -30,6 +40,7 @@ import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.util.ClassUtils;
 
 /**
  * Configuration for {@link HealthEndpoint} infrastructure beans.
@@ -61,8 +72,13 @@ class HealthEndpointConfiguration {
 
 	@Bean
 	@ConditionalOnMissingBean
-	HealthContributorRegistry healthContributorRegistry(Map<String, HealthContributor> healthContributors,
+	HealthContributorRegistry healthContributorRegistry(ApplicationContext applicationContext,
 			HealthEndpointGroups groups) {
+		Map<String, HealthContributor> healthContributors = new LinkedHashMap<>(
+				applicationContext.getBeansOfType(HealthContributor.class));
+		if (ClassUtils.isPresent("reactor.core.publisher.Flux", applicationContext.getClassLoader())) {
+			healthContributors.putAll(new AdaptedReactiveHealthContributors(applicationContext).get());
+		}
 		return new AutoConfiguredHealthContributorRegistry(healthContributors, groups.getNames());
 	}
 
@@ -72,4 +88,81 @@ class HealthEndpointConfiguration {
 		return new HealthEndpoint(registry, groups);
 	}
 
+	/**
+	 * Adapter to expose {@link ReactiveHealthContributor} beans as
+	 * {@link HealthContributor} instances.
+	 */
+	private static class AdaptedReactiveHealthContributors {
+
+		private final Map<String, HealthContributor> adapted;
+
+		AdaptedReactiveHealthContributors(ApplicationContext applicationContext) {
+			Map<String, HealthContributor> adapted = new LinkedHashMap<>();
+			applicationContext.getBeansOfType(ReactiveHealthContributor.class)
+					.forEach((name, contributor) -> adapted.put(name, adapt(contributor)));
+			this.adapted = Collections.unmodifiableMap(adapted);
+		}
+
+		private HealthContributor adapt(ReactiveHealthContributor contributor) {
+			if (contributor instanceof ReactiveHealthIndicator) {
+				return adapt((ReactiveHealthIndicator) contributor);
+			}
+			if (contributor instanceof CompositeReactiveHealthContributor) {
+				return adapt((CompositeReactiveHealthContributor) contributor);
+			}
+			throw new IllegalStateException("Unsupported ReactiveHealthContributor type " + contributor.getClass());
+		}
+
+		private HealthIndicator adapt(ReactiveHealthIndicator indicator) {
+			return new HealthIndicator() {
+
+				@Override
+				public Health getHealth(boolean includeDetails) {
+					return indicator.getHealth(includeDetails).block();
+				}
+
+				@Override
+				public Health health() {
+					return indicator.health().block();
+				}
+
+			};
+		}
+
+		private CompositeHealthContributor adapt(CompositeReactiveHealthContributor composite) {
+			return new CompositeHealthContributor() {
+
+				@Override
+				public Iterator<NamedContributor<HealthContributor>> iterator() {
+					Iterator<NamedContributor<ReactiveHealthContributor>> iterator = composite.iterator();
+					return new Iterator<NamedContributor<HealthContributor>>() {
+
+						@Override
+						public boolean hasNext() {
+							return iterator.hasNext();
+						}
+
+						@Override
+						public NamedContributor<HealthContributor> next() {
+							NamedContributor<ReactiveHealthContributor> next = iterator.next();
+							return NamedContributor.of(next.getName(), adapt(next.getContributor()));
+						}
+
+					};
+				}
+
+				@Override
+				public HealthContributor getContributor(String name) {
+					return adapt(composite.getContributor(name));
+				}
+
+			};
+		}
+
+		Map<String, HealthContributor> get() {
+			return this.adapted;
+		}
+
+	}
+
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/health/HealthEndpointAutoConfigurationTests.java

@@ -22,6 +22,7 @@ import java.util.List;
 import java.util.Map;
 
 import org.junit.jupiter.api.Test;
+import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
 import org.springframework.boot.actuate.endpoint.SecurityContext;
@@ -178,6 +179,16 @@ class HealthEndpointAutoConfigurationTests {
 	@Test
 	void runCreatesHealthContributorRegistryContainingHealthBeans() {
 		this.contextRunner.run((context) -> {
+			HealthContributorRegistry registry = context.getBean(HealthContributorRegistry.class);
+			Object[] names = registry.stream().map(NamedContributor::getName).toArray();
+			assertThat(names).containsExactlyInAnyOrder("simple", "additional", "ping", "reactive");
+		});
+	}
+
+	@Test
+	void runWhenNoReactorCreatesHealthContributorRegistryContainingHealthBeans() {
+		ClassLoader classLoader = new FilteredClassLoader(Mono.class, Flux.class);
+		this.contextRunner.withClassLoader(classLoader).run((context) -> {
 			HealthContributorRegistry registry = context.getBean(HealthContributorRegistry.class);
 			Object[] names = registry.stream().map(NamedContributor::getName).toArray();
 			assertThat(names).containsExactlyInAnyOrder("simple", "additional", "ping");