Support composite registries in MetricsEndpoint

Update `MetricsEndpoint` to deal with `CompositeMeterRegistry`
instances.

Closes gh-10535

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/MetricsEndpoint.java

@@ -16,11 +16,14 @@
 
 package org.springframework.boot.actuate.metrics;
 
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
@@ -29,6 +32,7 @@ import io.micrometer.core.instrument.Meter;
 import io.micrometer.core.instrument.MeterRegistry;
 import io.micrometer.core.instrument.Statistic;
 import io.micrometer.core.instrument.Tag;
+import io.micrometer.core.instrument.composite.CompositeMeterRegistry;
 
 import org.springframework.boot.actuate.endpoint.annotation.Endpoint;
 import org.springframework.boot.actuate.endpoint.annotation.ReadOperation;
@@ -52,9 +56,22 @@ public class MetricsEndpoint {
 	}
 
 	@ReadOperation
-	public Map<String, List<String>> listNames() {
+	public ListNamesResponse listNames() {
-		return Collections.singletonMap("names", this.registry.getMeters().stream()
+		return new ListNamesResponse(recurseListNames(this.registry));
-				.map(this::getMeterIdName).distinct().collect(Collectors.toList()));
+	}
+
+	private Set<String> recurseListNames(MeterRegistry registry) {
+		Set<String> names = new HashSet<>();
+		if (registry instanceof CompositeMeterRegistry) {
+			for (MeterRegistry compositeMember : ((CompositeMeterRegistry) registry)
+					.getRegistries()) {
+				names.addAll(recurseListNames(compositeMember));
+			}
+		}
+		else {
+			registry.getMeters().stream().map(this::getMeterIdName).forEach(names::add);
+		}
+		return names;
 	}
 
 	private String getMeterIdName(Meter meter) {
@@ -62,13 +79,12 @@ public class MetricsEndpoint {
 	}
 
 	@ReadOperation
-	public Response metric(@Selector String requiredMetricName,
+	public MetricResponse metric(@Selector String requiredMetricName,
 			@Nullable List<String> tag) {
 		Assert.isTrue(tag == null || tag.stream().allMatch((t) -> t.contains(":")),
 				"Each tag parameter must be in the form key:value");
 		List<Tag> tags = parseTags(tag);
-		Collection<Meter> meters = this.registry.find(requiredMetricName).tags(tags)
+		Collection<Meter> meters = recurseFindMeter(this.registry, requiredMetricName, tags);
-				.meters();
 		if (meters.isEmpty()) {
 			return null;
 		}
@@ -90,18 +106,32 @@ public class MetricsEndpoint {
 
 		tags.forEach((t) -> availableTags.remove(t.getKey()));
 
-		return new Response(requiredMetricName,
+		return new MetricResponse(requiredMetricName,
 				samples.entrySet().stream()
-						.map((sample) -> new Response.Sample(sample.getKey(),
+						.map((sample) -> new MetricResponse.Sample(sample.getKey(),
 								sample.getValue()))
-				.collect(
+						.collect(Collectors.toList()),
-						Collectors.toList()),
 				availableTags.entrySet().stream()
-						.map((tagValues) -> new Response.AvailableTag(tagValues.getKey(),
+						.map((tagValues) -> new MetricResponse.AvailableTag(
-								tagValues.getValue()))
+								tagValues.getKey(), tagValues.getValue()))
 						.collect(Collectors.toList()));
 	}
 
+	private Collection<Meter> recurseFindMeter(MeterRegistry registry, String name,
+			Iterable<Tag> tags) {
+		Collection<Meter> meters = new ArrayList<>();
+		if (registry instanceof CompositeMeterRegistry) {
+			for (MeterRegistry compositeMember : ((CompositeMeterRegistry) registry)
+					.getRegistries()) {
+				meters.addAll(recurseFindMeter(compositeMember, name, tags));
+			}
+		}
+		else {
+			meters.addAll(registry.find(name).tags(tags).meters());
+		}
+		return meters;
+	}
+
 	private List<Tag> parseTags(List<String> tags) {
 		return tags == null ? Collections.emptyList() : tags.stream().map((t) -> {
 			String[] tagParts = t.split(":", 2);
@@ -110,9 +140,25 @@ public class MetricsEndpoint {
 	}
 
 	/**
-	 * Response payload.
+	 * Response payload for a metric name listing.
 	 */
-	static class Response {
+	static class ListNamesResponse {
+
+		private final Set<String> names;
+
+		ListNamesResponse(Set<String> names) {
+			this.names = names;
+		}
+
+		public Set<String> getNames() {
+			return this.names;
+		}
+	}
+
+	/**
+	 * Response payload for a metric name selector.
+	 */
+	static class MetricResponse {
 
 		private final String name;
 
@@ -120,7 +166,7 @@ public class MetricsEndpoint {
 
 		private final List<AvailableTag> availableTags;
 
-		Response(String name, List<Sample> measurements,
+		MetricResponse(String name, List<Sample> measurements,
 				List<AvailableTag> availableTags) {
 			this.name = name;
 			this.measurements = measurements;

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/MetricsEndpointTests.java

@@ -17,13 +17,12 @@
 package org.springframework.boot.actuate.metrics;
 
 import java.util.Collections;
-import java.util.List;
-import java.util.Map;
 import java.util.Optional;
 import java.util.stream.Stream;
 
 import io.micrometer.core.instrument.MeterRegistry;
 import io.micrometer.core.instrument.Statistic;
+import io.micrometer.core.instrument.composite.CompositeMeterRegistry;
 import io.micrometer.core.instrument.simple.SimpleMeterRegistry;
 import org.junit.Test;
 
@@ -43,9 +42,8 @@ public class MetricsEndpointTests {
 
 	@Test
 	public void listNamesHandlesEmptyListOfMeters() {
-		Map<String, List<String>> result = this.endpoint.listNames();
+		MetricsEndpoint.ListNamesResponse result = this.endpoint.listNames();
-		assertThat(result).containsOnlyKeys("names");
+		assertThat(result.getNames()).isEmpty();
-		assertThat(result.get("names")).isEmpty();
 	}
 
 	@Test
@@ -53,18 +51,32 @@ public class MetricsEndpointTests {
 		this.registry.counter("com.example.foo");
 		this.registry.counter("com.example.bar");
 		this.registry.counter("com.example.foo");
-		Map<String, List<String>> result = this.endpoint.listNames();
+		MetricsEndpoint.ListNamesResponse result = this.endpoint.listNames();
-		assertThat(result).containsOnlyKeys("names");
+		assertThat(result.getNames()).containsOnlyOnce("com.example.foo",
-		assertThat(result.get("names")).containsOnlyOnce("com.example.foo",
 				"com.example.bar");
 	}
 
+	@Test
+	public void listNamesRecursesOverCompositeRegistries() {
+		CompositeMeterRegistry composite = new CompositeMeterRegistry();
+		SimpleMeterRegistry reg1 = new SimpleMeterRegistry();
+		SimpleMeterRegistry reg2 = new SimpleMeterRegistry();
+		composite.add(reg1);
+		composite.add(reg2);
+
+		reg1.counter("counter1").increment();
+		reg2.counter("counter2").increment();
+
+		MetricsEndpoint endpoint = new MetricsEndpoint(composite);
+		assertThat(endpoint.listNames().getNames()).containsOnly("counter1", "counter2");
+	}
+
 	@Test
 	public void metricValuesAreTheSumOfAllTimeSeriesMatchingTags() {
 		this.registry.counter("cache", "result", "hit", "host", "1").increment(2);
 		this.registry.counter("cache", "result", "miss", "host", "1").increment(2);
 		this.registry.counter("cache", "result", "hit", "host", "2").increment(2);
-		MetricsEndpoint.Response response = this.endpoint.metric("cache",
+		MetricsEndpoint.MetricResponse response = this.endpoint.metric("cache",
 				Collections.emptyList());
 		assertThat(response.getName()).isEqualTo("cache");
 		assertThat(availableTagKeys(response)).containsExactly("result", "host");
@@ -77,29 +89,45 @@ public class MetricsEndpointTests {
 	@Test
 	public void metricWithSpaceInTagValue() {
 		this.registry.counter("counter", "key", "a space").increment(2);
-		MetricsEndpoint.Response response = this.endpoint.metric("counter",
+		MetricsEndpoint.MetricResponse response = this.endpoint.metric("counter",
 				Collections.singletonList("key:a space"));
 		assertThat(response.getName()).isEqualTo("counter");
 		assertThat(availableTagKeys(response)).isEmpty();
 		assertThat(getCount(response)).hasValue(2.0);
 	}
 
+	@Test
+	public void metricPresentInOneRegistryOfACompositeAndNotAnother() {
+		CompositeMeterRegistry composite = new CompositeMeterRegistry();
+		SimpleMeterRegistry reg1 = new SimpleMeterRegistry();
+		SimpleMeterRegistry reg2 = new SimpleMeterRegistry();
+		composite.add(reg1);
+		composite.add(reg2);
+
+		reg1.counter("counter1").increment();
+		reg2.counter("counter2").increment();
+
+		MetricsEndpoint endpoint = new MetricsEndpoint(composite);
+		assertThat(endpoint.metric("counter1", Collections.emptyList())).isNotNull();
+		assertThat(endpoint.metric("counter2", Collections.emptyList())).isNotNull();
+	}
+
 	@Test
 	public void nonExistentMetric() {
-		MetricsEndpoint.Response response = this.endpoint.metric("does.not.exist",
+		MetricsEndpoint.MetricResponse response = this.endpoint.metric("does.not.exist",
 				Collections.emptyList());
 		assertThat(response).isNull();
 	}
 
-	private Optional<Double> getCount(MetricsEndpoint.Response response) {
+	private Optional<Double> getCount(MetricsEndpoint.MetricResponse response) {
 		return response.getMeasurements().stream()
 				.filter((ms) -> ms.getStatistic().equals(Statistic.Count)).findAny()
-				.map(MetricsEndpoint.Response.Sample::getValue);
+				.map(MetricsEndpoint.MetricResponse.Sample::getValue);
 	}
 
-	private Stream<String> availableTagKeys(MetricsEndpoint.Response response) {
+	private Stream<String> availableTagKeys(MetricsEndpoint.MetricResponse response) {
 		return response.getAvailableTags().stream()
-				.map(MetricsEndpoint.Response.AvailableTag::getTag);
+				.map(MetricsEndpoint.MetricResponse.AvailableTag::getTag);
 	}
 
 }