Restore AbstractRoutingDataSource health support

Update `DataSourceHealthContributorAutoConfiguration` so that any
`AbstractRoutingDataSource` beans are still included in the overall
health. Prior to this commit, a regression in Spring Boot 2.2 meant
that if a single routing bean was found an `IllegalArgumentException`
would be thrown.

In Spring Boot 2.1 all `AbstractRoutingDataSource` would be filtered
from the results, but if no results existed the following was returned:

  "details": {
    "db": {
      "status": "UNKNOWN"
    },

In Spring Boot 2.2 we now always include routing datasource beans, even
if other non-routing database beans are found. The health details
includes `"routing" : true` to help users disambiguate any results.

Fixes gh-18661

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/jdbc/DataSourceHealthContributorAutoConfiguration.java

@@ -17,7 +17,6 @@
 package org.springframework.boot.actuate.autoconfigure.jdbc;
 
 import java.util.Collection;
-import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.stream.Collectors;
 
@@ -27,7 +26,10 @@ import org.springframework.beans.factory.InitializingBean;
 import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.actuate.autoconfigure.health.CompositeHealthContributorConfiguration;
 import org.springframework.boot.actuate.autoconfigure.health.ConditionalOnEnabledHealthIndicator;
+import org.springframework.boot.actuate.health.AbstractHealthIndicator;
+import org.springframework.boot.actuate.health.Health.Builder;
 import org.springframework.boot.actuate.health.HealthContributor;
+import org.springframework.boot.actuate.health.HealthIndicator;
 import org.springframework.boot.actuate.jdbc.DataSourceHealthIndicator;
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
@@ -60,7 +62,7 @@ import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;
 @ConditionalOnEnabledHealthIndicator("db")
 @AutoConfigureAfter(DataSourceAutoConfiguration.class)
 public class DataSourceHealthContributorAutoConfiguration extends
-		CompositeHealthContributorConfiguration<DataSourceHealthIndicator, DataSource> implements InitializingBean {
+		CompositeHealthContributorConfiguration<AbstractHealthIndicator, DataSource> implements InitializingBean {
 
 	private final Collection<DataSourcePoolMetadataProvider> metadataProviders;
 
@@ -79,24 +81,14 @@ public class DataSourceHealthContributorAutoConfiguration extends
 	@Bean
 	@ConditionalOnMissingBean(name = { "dbHealthIndicator", "dbHealthContributor" })
 	public HealthContributor dbHealthContributor(Map<String, DataSource> dataSources) {
-		return createContributor(filterDataSources(dataSources));
-	}
-
-	private Map<String, DataSource> filterDataSources(Map<String, DataSource> candidates) {
-		if (candidates == null) {
-			return null;
-		}
-		Map<String, DataSource> dataSources = new LinkedHashMap<>();
-		candidates.forEach((name, dataSource) -> {
-			if (!(dataSource instanceof AbstractRoutingDataSource)) {
-				dataSources.put(name, dataSource);
-			}
-		});
-		return dataSources;
+		return createContributor(dataSources);
 	}
 
 	@Override
-	protected DataSourceHealthIndicator createIndicator(DataSource source) {
+	protected AbstractHealthIndicator createIndicator(DataSource source) {
+		if (source instanceof AbstractRoutingDataSource) {
+			return new RoutingDataSourceHealthIndicator();
+		}
 		return new DataSourceHealthIndicator(source, getValidationQuery(source));
 	}
 
@@ -105,4 +97,17 @@ public class DataSourceHealthContributorAutoConfiguration extends
 		return (poolMetadata != null) ? poolMetadata.getValidationQuery() : null;
 	}
 
+	/**
+	 * {@link HealthIndicator} used for {@link AbstractRoutingDataSource} beans where we
+	 * can't actually query for the status.
+	 */
+	static class RoutingDataSourceHealthIndicator extends AbstractHealthIndicator {
+
+		@Override
+		protected void doHealthCheck(Builder builder) throws Exception {
+			builder.unknown().withDetail("routing", true);
+		}
+
+	}
+
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/jdbc/DataSourceHealthContributorAutoConfigurationTests.java

@@ -21,6 +21,7 @@ import javax.sql.DataSource;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.actuate.autoconfigure.health.HealthContributorAutoConfiguration;
+import org.springframework.boot.actuate.autoconfigure.jdbc.DataSourceHealthContributorAutoConfiguration.RoutingDataSourceHealthIndicator;
 import org.springframework.boot.actuate.health.CompositeHealthContributor;
 import org.springframework.boot.actuate.health.NamedContributor;
 import org.springframework.boot.actuate.jdbc.DataSourceHealthIndicator;
@@ -71,10 +72,20 @@ class DataSourceHealthContributorAutoConfigurationTests {
 	}
 
 	@Test
-	void runShouldFilterRoutingDataSource() {
+	void runWithRoutingAndEmbeddedDataSourceShouldFilterRoutingDataSource() {
 		this.contextRunner.withUserConfiguration(EmbeddedDataSourceConfiguration.class, RoutingDatasourceConfig.class)
-				.run((context) -> assertThat(context).hasSingleBean(DataSourceHealthIndicator.class)
-						.doesNotHaveBean(CompositeHealthContributor.class));
+				.run((context) -> {
+					CompositeHealthContributor composite = context.getBean(CompositeHealthContributor.class);
+					assertThat(composite.getContributor("dataSource")).isInstanceOf(DataSourceHealthIndicator.class);
+					assertThat(composite.getContributor("routingDataSource"))
+							.isInstanceOf(RoutingDataSourceHealthIndicator.class);
+				});
+	}
+
+	@Test
+	void runWithOnlyRoutingDataSourceShouldFilterRoutingDataSource() {
+		this.contextRunner.withUserConfiguration(RoutingDatasourceConfig.class)
+				.run((context) -> assertThat(context).hasSingleBean(RoutingDataSourceHealthIndicator.class));
 	}
 
 	@Test