Fix PropertiesConfigAdapter delegation logic

This change replaces fallback logic in PropertiesConfigAdapter and its
descendants such that instead of falling back to default "empty" config
it delegates to superinterface default implementation of the same class.

This allows default implementation to call back to other properties,
like DatadogConfig.uri() does.

See gh-11135

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/export/PropertiesConfigAdapter.java

@@ -17,6 +17,7 @@
 package org.springframework.boot.actuate.autoconfigure.metrics.export;
 
 import java.util.function.Function;
+import java.util.function.Supplier;
 
 import org.springframework.util.Assert;
 
@@ -24,38 +25,32 @@ import org.springframework.util.Assert;
  * Base class for properties to config adapters.
  *
  * @param <T> The properties type
- * @param <C> The config type
  * @author Phillip Webb
  * @since 2.0.0
  */
-public class PropertiesConfigAdapter<T, C> {
+public class PropertiesConfigAdapter<T> {
 
 	private T properties;
 
-	private C defaults;
-
 	/**
 	 * Create a new {@link PropertiesConfigAdapter} instance.
 	 * @param properties the source properties
-	 * @param defaults a config implementation providing default values
 	 */
-	public PropertiesConfigAdapter(T properties, C defaults) {
+	public PropertiesConfigAdapter(T properties) {
 		Assert.notNull(properties, "Properties must not be null");
-		Assert.notNull(defaults, "Defaults must not be null");
 		this.properties = properties;
-		this.defaults = defaults;
 	}
 
 	/**
 	 * Get the value from the properties or use a fallback from the {@code defaults}.
 	 * @param getter the getter for the properties
-	 * @param fallback the fallback method from the {@code defaults}
+	 * @param fallback the fallback method, usually super interface method reference
 	 * @param <V> the value type
 	 * @return the property or fallback value
 	 */
-	protected final <V> V get(Function<T, V> getter, Function<C, V> fallback) {
+	protected final <V> V get(Function<T, V> getter, Supplier<V> fallback) {
 		V value = getter.apply(this.properties);
-		return (value != null ? value : fallback.apply(this.defaults));
+		return (value != null ? value : fallback.get());
 	}
 
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/export/StepRegistryPropertiesConfigAdapter.java

@@ -24,16 +24,15 @@ import io.micrometer.core.instrument.step.StepRegistryConfig;
  * Base class for {@link StepRegistryProperties} to {@link StepRegistryConfig} adapters.
  *
  * @param <T> The properties type
- * @param <C> The config type
  * @author Jon Schneider
  * @author Phillip Webb
  * @since 2.0.0
  */
-public abstract class StepRegistryPropertiesConfigAdapter<T extends StepRegistryProperties, C extends StepRegistryConfig>
-		extends PropertiesConfigAdapter<T, C> implements StepRegistryConfig {
+public abstract class StepRegistryPropertiesConfigAdapter<T extends StepRegistryProperties>
+		extends PropertiesConfigAdapter<T> implements StepRegistryConfig {
 
-	public StepRegistryPropertiesConfigAdapter(T properties, C defaults) {
-		super(properties, defaults);
+	public StepRegistryPropertiesConfigAdapter(T properties) {
+		super(properties);
 	}
 
 	@Override
@@ -48,32 +47,32 @@ public abstract class StepRegistryPropertiesConfigAdapter<T extends StepRegistry
 
 	@Override
 	public Duration step() {
-		return get(T::getStep, C::step);
+		return get(T::getStep, StepRegistryConfig.super::step);
 	}
 
 	@Override
 	public boolean enabled() {
-		return get(T::getEnabled, C::enabled);
+		return get(T::getEnabled, StepRegistryConfig.super::enabled);
 	}
 
 	@Override
 	public Duration connectTimeout() {
-		return get(T::getConnectTimeout, C::connectTimeout);
+		return get(T::getConnectTimeout, StepRegistryConfig.super::connectTimeout);
 	}
 
 	@Override
 	public Duration readTimeout() {
-		return get(T::getReadTimeout, C::readTimeout);
+		return get(T::getReadTimeout, StepRegistryConfig.super::readTimeout);
 	}
 
 	@Override
 	public int numThreads() {
-		return get(T::getNumThreads, C::numThreads);
+		return get(T::getNumThreads, StepRegistryConfig.super::numThreads);
 	}
 
 	@Override
 	public int batchSize() {
-		return get(T::getBatchSize, C::batchSize);
+		return get(T::getBatchSize, StepRegistryConfig.super::batchSize);
 	}
 
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/export/atlas/AtlasPropertiesConfigAdapter.java

@@ -29,12 +29,10 @@ import org.springframework.boot.actuate.autoconfigure.metrics.export.PropertiesC
  * @author Phillip Webb
  */
 class AtlasPropertiesConfigAdapter extends
-		PropertiesConfigAdapter<AtlasProperties, AtlasConfig> implements AtlasConfig {
-
-	private static final AtlasConfig DEFAULTS = (k) -> null;
+		PropertiesConfigAdapter<AtlasProperties> implements AtlasConfig {
 
 	AtlasPropertiesConfigAdapter(AtlasProperties properties) {
-		super(properties, DEFAULTS);
+		super(properties);
 	}
 
 	@Override
@@ -44,68 +42,68 @@ class AtlasPropertiesConfigAdapter extends
 
 	@Override
 	public Duration step() {
-		return get(AtlasProperties::getStep, AtlasConfig::step);
+		return get(AtlasProperties::getStep, AtlasConfig.super::step);
 	}
 
 	@Override
 	public boolean enabled() {
-		return get(AtlasProperties::getEnabled, AtlasConfig::enabled);
+		return get(AtlasProperties::getEnabled, AtlasConfig.super::enabled);
 	}
 
 	@Override
 	public Duration connectTimeout() {
-		return get(AtlasProperties::getConnectTimeout, AtlasConfig::connectTimeout);
+		return get(AtlasProperties::getConnectTimeout, AtlasConfig.super::connectTimeout);
 	}
 
 	@Override
 	public Duration readTimeout() {
-		return get(AtlasProperties::getReadTimeout, AtlasConfig::readTimeout);
+		return get(AtlasProperties::getReadTimeout, AtlasConfig.super::readTimeout);
 	}
 
 	@Override
 	public int numThreads() {
-		return get(AtlasProperties::getNumThreads, AtlasConfig::numThreads);
+		return get(AtlasProperties::getNumThreads, AtlasConfig.super::numThreads);
 	}
 
 	@Override
 	public int batchSize() {
-		return get(AtlasProperties::getBatchSize, AtlasConfig::batchSize);
+		return get(AtlasProperties::getBatchSize, AtlasConfig.super::batchSize);
 	}
 
 	@Override
 	public String uri() {
-		return get(AtlasProperties::getUri, AtlasConfig::uri);
+		return get(AtlasProperties::getUri, AtlasConfig.super::uri);
 	}
 
 	@Override
 	public Duration meterTTL() {
-		return get(AtlasProperties::getMeterTimeToLive, AtlasConfig::meterTTL);
+		return get(AtlasProperties::getMeterTimeToLive, AtlasConfig.super::meterTTL);
 	}
 
 	@Override
 	public boolean lwcEnabled() {
-		return get(AtlasProperties::getLwcEnabled, AtlasConfig::lwcEnabled);
+		return get(AtlasProperties::getLwcEnabled, AtlasConfig.super::lwcEnabled);
 	}
 
 	@Override
 	public Duration configRefreshFrequency() {
 		return get(AtlasProperties::getConfigRefreshFrequency,
-				AtlasConfig::configRefreshFrequency);
+				AtlasConfig.super::configRefreshFrequency);
 	}
 
 	@Override
 	public Duration configTTL() {
-		return get(AtlasProperties::getConfigTimeToLive, AtlasConfig::configTTL);
+		return get(AtlasProperties::getConfigTimeToLive, AtlasConfig.super::configTTL);
 	}
 
 	@Override
 	public String configUri() {
-		return get(AtlasProperties::getConfigUri, AtlasConfig::configUri);
+		return get(AtlasProperties::getConfigUri, AtlasConfig.super::configUri);
 	}
 
 	@Override
 	public String evalUri() {
-		return get(AtlasProperties::getEvalUri, AtlasConfig::evalUri);
+		return get(AtlasProperties::getEvalUri, AtlasConfig.super::evalUri);
 	}
 
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/export/datadog/DatadogPropertiesConfigAdapter.java

@@ -27,28 +27,26 @@ import org.springframework.boot.actuate.autoconfigure.metrics.export.StepRegistr
  * @author Phillip Webb
  */
 class DatadogPropertiesConfigAdapter
-		extends StepRegistryPropertiesConfigAdapter<DatadogProperties, DatadogConfig>
+		extends StepRegistryPropertiesConfigAdapter<DatadogProperties>
 		implements DatadogConfig {
 
-	private static final DatadogConfig DEFAULTS = (k) -> null;
-
 	DatadogPropertiesConfigAdapter(DatadogProperties properties) {
-		super(properties, DEFAULTS);
+		super(properties);
 	}
 
 	@Override
 	public String apiKey() {
-		return get(DatadogProperties::getApiKey, DatadogConfig::apiKey);
+		return get(DatadogProperties::getApiKey, DatadogConfig.super::apiKey);
 	}
 
 	@Override
 	public String hostTag() {
-		return get(DatadogProperties::getHostTag, DatadogConfig::hostTag);
+		return get(DatadogProperties::getHostTag, DatadogConfig.super::hostTag);
 	}
 
 	@Override
 	public String uri() {
-		return get(DatadogProperties::getUri, DatadogConfig::uri);
+		return get(DatadogProperties::getUri, DatadogConfig.super::uri);
 	}
 
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/export/ganglia/GangliaPropertiesConfigAdapter.java

@@ -31,13 +31,11 @@ import org.springframework.boot.actuate.autoconfigure.metrics.export.PropertiesC
  * @author Phillip Webb
  */
 class GangliaPropertiesConfigAdapter
-		extends PropertiesConfigAdapter<GangliaProperties, GangliaConfig>
+		extends PropertiesConfigAdapter<GangliaProperties>
 		implements GangliaConfig {
 
-	private static final GangliaConfig DEFAULTS = (k) -> null;
-
 	GangliaPropertiesConfigAdapter(GangliaProperties properties) {
-		super(properties, DEFAULTS);
+		super(properties);
 	}
 
 	@Override
@@ -47,47 +45,47 @@ class GangliaPropertiesConfigAdapter
 
 	@Override
 	public boolean enabled() {
-		return get(GangliaProperties::getEnabled, GangliaConfig::enabled);
+		return get(GangliaProperties::getEnabled, GangliaConfig.super::enabled);
 	}
 
 	@Override
 	public Duration step() {
-		return get(GangliaProperties::getStep, GangliaConfig::step);
+		return get(GangliaProperties::getStep, GangliaConfig.super::step);
 	}
 
 	@Override
 	public TimeUnit rateUnits() {
-		return get(GangliaProperties::getRateUnits, GangliaConfig::rateUnits);
+		return get(GangliaProperties::getRateUnits, GangliaConfig.super::rateUnits);
 	}
 
 	@Override
 	public TimeUnit durationUnits() {
-		return get(GangliaProperties::getDurationUnits, GangliaConfig::durationUnits);
+		return get(GangliaProperties::getDurationUnits, GangliaConfig.super::durationUnits);
 	}
 
 	@Override
 	public String protocolVersion() {
-		return get(GangliaProperties::getProtocolVersion, GangliaConfig::protocolVersion);
+		return get(GangliaProperties::getProtocolVersion, GangliaConfig.super::protocolVersion);
 	}
 
 	@Override
 	public GMetric.UDPAddressingMode addressingMode() {
-		return get(GangliaProperties::getAddressingMode, GangliaConfig::addressingMode);
+		return get(GangliaProperties::getAddressingMode, GangliaConfig.super::addressingMode);
 	}
 
 	@Override
 	public int ttl() {
-		return get(GangliaProperties::getTimeToLive, GangliaConfig::ttl);
+		return get(GangliaProperties::getTimeToLive, GangliaConfig.super::ttl);
 	}
 
 	@Override
 	public String host() {
-		return get(GangliaProperties::getHost, GangliaConfig::host);
+		return get(GangliaProperties::getHost, GangliaConfig.super::host);
 	}
 
 	@Override
 	public int port() {
-		return get(GangliaProperties::getPort, GangliaConfig::port);
+		return get(GangliaProperties::getPort, GangliaConfig.super::port);
 	}
 
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/export/graphite/GraphitePropertiesConfigAdapter.java

@@ -31,13 +31,11 @@ import org.springframework.boot.actuate.autoconfigure.metrics.export.PropertiesC
  * @author Phillip Webb
  */
 class GraphitePropertiesConfigAdapter
-		extends PropertiesConfigAdapter<GraphiteProperties, GraphiteConfig>
+		extends PropertiesConfigAdapter<GraphiteProperties>
 		implements GraphiteConfig {
 
-	private static final GraphiteConfig DEFAULTS = (k) -> null;
-
 	GraphitePropertiesConfigAdapter(GraphiteProperties properties) {
-		super(properties, DEFAULTS);
+		super(properties);
 	}
 
 	@Override
@@ -47,37 +45,37 @@ class GraphitePropertiesConfigAdapter
 
 	@Override
 	public boolean enabled() {
-		return get(GraphiteProperties::getEnabled, GraphiteConfig::enabled);
+		return get(GraphiteProperties::getEnabled, GraphiteConfig.super::enabled);
 	}
 
 	@Override
 	public Duration step() {
-		return get(GraphiteProperties::getStep, GraphiteConfig::step);
+		return get(GraphiteProperties::getStep, GraphiteConfig.super::step);
 	}
 
 	@Override
 	public TimeUnit rateUnits() {
-		return get(GraphiteProperties::getRateUnits, GraphiteConfig::rateUnits);
+		return get(GraphiteProperties::getRateUnits, GraphiteConfig.super::rateUnits);
 	}
 
 	@Override
 	public TimeUnit durationUnits() {
-		return get(GraphiteProperties::getDurationUnits, GraphiteConfig::durationUnits);
+		return get(GraphiteProperties::getDurationUnits, GraphiteConfig.super::durationUnits);
 	}
 
 	@Override
 	public String host() {
-		return get(GraphiteProperties::getHost, GraphiteConfig::host);
+		return get(GraphiteProperties::getHost, GraphiteConfig.super::host);
 	}
 
 	@Override
 	public int port() {
-		return get(GraphiteProperties::getPort, GraphiteConfig::port);
+		return get(GraphiteProperties::getPort, GraphiteConfig.super::port);
 	}
 
 	@Override
 	public GraphiteProtocol protocol() {
-		return get(GraphiteProperties::getProtocol, GraphiteConfig::protocol);
+		return get(GraphiteProperties::getProtocol, GraphiteConfig.super::protocol);
 	}
 
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/export/influx/InfluxPropertiesConfigAdapter.java

@@ -28,48 +28,46 @@ import org.springframework.boot.actuate.autoconfigure.metrics.export.StepRegistr
  * @author Phillip Webb
  */
 class InfluxPropertiesConfigAdapter
-		extends StepRegistryPropertiesConfigAdapter<InfluxProperties, InfluxConfig>
+		extends StepRegistryPropertiesConfigAdapter<InfluxProperties>
 		implements InfluxConfig {
 
-	private static final InfluxConfig DEFAULTS = (k) -> null;
-
 	InfluxPropertiesConfigAdapter(InfluxProperties properties) {
-		super(properties, DEFAULTS);
+		super(properties);
 	}
 
 	@Override
 	public String db() {
-		return get(InfluxProperties::getDb, InfluxConfig::db);
+		return get(InfluxProperties::getDb, InfluxConfig.super::db);
 	}
 
 	@Override
 	public InfluxConsistency consistency() {
-		return get(InfluxProperties::getConsistency, InfluxConfig::consistency);
+		return get(InfluxProperties::getConsistency, InfluxConfig.super::consistency);
 	}
 
 	@Override
 	public String userName() {
-		return get(InfluxProperties::getUserName, InfluxConfig::userName);
+		return get(InfluxProperties::getUserName, InfluxConfig.super::userName);
 	}
 
 	@Override
 	public String password() {
-		return get(InfluxProperties::getPassword, InfluxConfig::password);
+		return get(InfluxProperties::getPassword, InfluxConfig.super::password);
 	}
 
 	@Override
 	public String retentionPolicy() {
-		return get(InfluxProperties::getRetentionPolicy, InfluxConfig::retentionPolicy);
+		return get(InfluxProperties::getRetentionPolicy, InfluxConfig.super::retentionPolicy);
 	}
 
 	@Override
 	public String uri() {
-		return get(InfluxProperties::getUri, InfluxConfig::uri);
+		return get(InfluxProperties::getUri, InfluxConfig.super::uri);
 	}
 
 	@Override
 	public boolean compressed() {
-		return get(InfluxProperties::getCompressed, InfluxConfig::compressed);
+		return get(InfluxProperties::getCompressed, InfluxConfig.super::compressed);
 	}
 
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/export/prometheus/PrometheusPropertiesConfigAdapter.java

@@ -29,13 +29,11 @@ import org.springframework.boot.actuate.autoconfigure.metrics.export.PropertiesC
  * @author Phillip Webb
  */
 class PrometheusPropertiesConfigAdapter
-		extends PropertiesConfigAdapter<PrometheusProperties, PrometheusConfig>
+		extends PropertiesConfigAdapter<PrometheusProperties>
 		implements PrometheusConfig {
 
-	private static final PrometheusConfig DEFAULTS = (key) -> null;
-
 	PrometheusPropertiesConfigAdapter(PrometheusProperties properties) {
-		super(properties, DEFAULTS);
+		super(properties);
 	}
 
 	@Override
@@ -45,12 +43,12 @@ class PrometheusPropertiesConfigAdapter
 
 	@Override
 	public boolean descriptions() {
-		return get(PrometheusProperties::getDescriptions, PrometheusConfig::descriptions);
+		return get(PrometheusProperties::getDescriptions, PrometheusConfig.super::descriptions);
 	}
 
 	@Override
 	public Duration step() {
-		return get(PrometheusProperties::getStep, PrometheusConfig::step);
+		return get(PrometheusProperties::getStep, PrometheusConfig.super::step);
 	}
 
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/export/simple/SimplePropertiesConfigAdapter.java

@@ -29,11 +29,10 @@ import org.springframework.boot.actuate.autoconfigure.metrics.export.PropertiesC
  * @since 2.0.0
  */
 public class SimplePropertiesConfigAdapter extends
-		PropertiesConfigAdapter<SimpleProperties, SimpleConfig> implements SimpleConfig {
-	private static final SimpleConfig DEFAULTS = (key) -> null;
+		PropertiesConfigAdapter<SimpleProperties> implements SimpleConfig {
 
 	public SimplePropertiesConfigAdapter(SimpleProperties properties) {
-		super(properties, DEFAULTS);
+		super(properties);
 	}
 
 	@Override
@@ -43,11 +42,11 @@ public class SimplePropertiesConfigAdapter extends
 
 	@Override
 	public boolean enabled() {
-		return get(SimpleProperties::getEnabled, SimpleConfig::enabled);
+		return get(SimpleProperties::getEnabled, SimpleConfig.super::enabled);
 	}
 
 	@Override
 	public Duration step() {
-		return get(SimpleProperties::getStep, SimpleConfig::step);
+		return get(SimpleProperties::getStep, SimpleConfig.super::step);
 	}
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/export/statsd/StatsdPropertiesConfigAdapter.java

@@ -30,12 +30,10 @@ import org.springframework.boot.actuate.autoconfigure.metrics.export.PropertiesC
  * @since 2.0.0
  */
 public class StatsdPropertiesConfigAdapter extends
-		PropertiesConfigAdapter<StatsdProperties, StatsdConfig> implements StatsdConfig {
-
-	private static final StatsdConfig DEFAULTS = (key) -> null;
+		PropertiesConfigAdapter<StatsdProperties> implements StatsdConfig {
 
 	public StatsdPropertiesConfigAdapter(StatsdProperties properties) {
-		super(properties, DEFAULTS);
+		super(properties);
 	}
 
 	@Override
@@ -45,37 +43,37 @@ public class StatsdPropertiesConfigAdapter extends
 
 	@Override
 	public StatsdFlavor flavor() {
-		return get(StatsdProperties::getFlavor, StatsdConfig::flavor);
+		return get(StatsdProperties::getFlavor, StatsdConfig.super::flavor);
 	}
 
 	@Override
 	public boolean enabled() {
-		return get(StatsdProperties::getEnabled, StatsdConfig::enabled);
+		return get(StatsdProperties::getEnabled, StatsdConfig.super::enabled);
 	}
 
 	@Override
 	public String host() {
-		return get(StatsdProperties::getHost, StatsdConfig::host);
+		return get(StatsdProperties::getHost, StatsdConfig.super::host);
 	}
 
 	@Override
 	public int port() {
-		return get(StatsdProperties::getPort, StatsdConfig::port);
+		return get(StatsdProperties::getPort, StatsdConfig.super::port);
 	}
 
 	@Override
 	public int maxPacketLength() {
-		return get(StatsdProperties::getMaxPacketLength, StatsdConfig::maxPacketLength);
+		return get(StatsdProperties::getMaxPacketLength, StatsdConfig.super::maxPacketLength);
 	}
 
 	@Override
 	public Duration pollingFrequency() {
-		return get(StatsdProperties::getPollingFrequency, StatsdConfig::pollingFrequency);
+		return get(StatsdProperties::getPollingFrequency, StatsdConfig.super::pollingFrequency);
 	}
 
 	@Override
 	public int queueSize() {
-		return get(StatsdProperties::getQueueSize, StatsdConfig::queueSize);
+		return get(StatsdProperties::getQueueSize, StatsdConfig.super::queueSize);
 	}
 
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/export/datadog/DatadogExportConfigurationTests.java

+/*
+ * Copyright 2012-2017 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
+ *
+ *      http://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.actuate.autoconfigure.metrics.export.datadog;
+
+import io.micrometer.core.instrument.composite.CompositeMeterRegistry;
+import io.micrometer.datadog.DatadogMeterRegistry;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.boot.actuate.autoconfigure.metrics.MetricsAutoConfiguration;
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link DatadogExportConfiguration}.
+ *
+ * @author Nikolay Rybak
+ */
+@RunWith(SpringRunner.class)
+public class DatadogExportConfigurationTests {
+
+	/**
+	 * Validated that {@link DatadogMeterRegistry} can be started by only specifying Datadog API key.
+	 */
+	@Test
+	public void datadogMeterRegistryIsConfiguredWithApiKeyOnly() {
+		new ApplicationContextRunner()
+				.withPropertyValues("spring.metrics.export.atlas.enabled=false",
+						"spring.metrics.export.datadog.enabled=true",
+						"spring.metrics.export.ganglia.enabled=false",
+						"spring.metrics.export.graphite.enabled=false",
+						"spring.metrics.export.influx.enabled=false",
+						"spring.metrics.export.jmx.enabled=false",
+						"spring.metrics.export.prometheus.enabled=false",
+						"spring.metrics.export.statsd.enabled=false",
+						"spring.metrics.export.datadog.api-key=APIKEY")
+				.withConfiguration(AutoConfigurations.of(MetricsAutoConfiguration.class))
+				.run((context) -> {
+					CompositeMeterRegistry meterRegistry = context
+							.getBean(CompositeMeterRegistry.class);
+					assertThat(meterRegistry.getRegistries()).hasSize(1);
+					assertThat(meterRegistry.getRegistries())
+							.hasOnlyElementsOfType(DatadogMeterRegistry.class);
+				});
+	}
+
+}