Merge pull request #11492 from jkschneider:metrics-endpoint-tag-dedup

* pr/11492:
  Polish "Deduplicate tag values in metrics actuator endpoint"
  Deduplicate tag values in metrics actuator endpoint

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

 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -19,6 +19,7 @@ package org.springframework.boot.actuate.metrics;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
@@ -88,7 +89,7 @@ public class MetricsEndpoint {
 			return null;
 		}
 		Map<Statistic, Double> samples = getSamples(meters);
-		Map<String, List<String>> availableTags = getAvailableTags(meters);
+		Map<String, Set<String>> availableTags = getAvailableTags(meters);
 		tags.forEach((t) -> availableTags.remove(t.getKey()));
 		return new MetricResponse(requiredMetricName,
 				asList(samples, MetricResponse.Sample::new),
@@ -124,24 +125,24 @@ public class MetricsEndpoint {
 				measurement.getValue(), Double::sum));
 	}
 
-	private Map<String, List<String>> getAvailableTags(List<Meter> meters) {
-		Map<String, List<String>> availableTags = new HashMap<>();
+	private Map<String, Set<String>> getAvailableTags(List<Meter> meters) {
+		Map<String, Set<String>> availableTags = new HashMap<>();
 		meters.forEach((meter) -> mergeAvailableTags(availableTags, meter));
 		return availableTags;
 	}
 
-	private void mergeAvailableTags(Map<String, List<String>> availableTags,
+	private void mergeAvailableTags(Map<String, Set<String>> availableTags,
 			Meter meter) {
 		meter.getId().getTags().forEach((tag) -> {
-			List<String> value = Collections.singletonList(tag.getValue());
+			Set<String> value = Collections.singleton(tag.getValue());
 			availableTags.merge(tag.getKey(), value, this::merge);
 		});
 	}
 
-	private <T> List<T> merge(List<T> list1, List<T> list2) {
-		List<T> result = new ArrayList<>(list1.size() + list2.size());
-		result.addAll(list1);
-		result.addAll(list2);
+	private <T> Set<T> merge(Set<T> set1, Set<T> set2) {
+		Set<T> result = new HashSet<>(set1.size() + set2.size());
+		result.addAll(set1);
+		result.addAll(set2);
 		return result;
 	}
 
@@ -204,9 +205,9 @@ public class MetricsEndpoint {
 
 			private final String tag;
 
-			private final List<String> values;
+			private final Set<String> values;
 
-			AvailableTag(String tag, List<String> values) {
+			AvailableTag(String tag, Set<String> values) {
 				this.tag = tag;
 				this.values = values;
 			}
@@ -215,7 +216,7 @@ public class MetricsEndpoint {
 				return this.tag;
 			}
 
-			public List<String> getValues() {
+			public Set<String> getValues() {
 				return this.values;
 			}
 		}

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

@@ -87,6 +87,19 @@ public class MetricsEndpointTests {
 		assertThat(getCount(response)).hasValue(4.0);
 	}
 
+	@Test
+	public void metricTagValuesAreDeduplicated() {
+		this.registry.counter("cache", "host", "1", "region", "east", "result", "hit");
+		this.registry.counter("cache", "host", "1", "region", "east", "result", "miss");
+		MetricsEndpoint.MetricResponse response = this.endpoint.metric("cache",
+				Collections.singletonList("host:1"));
+		assertThat(response.getAvailableTags()
+				.stream()
+				.filter(t -> t.getTag().equals("region"))
+				.flatMap(t -> t.getValues().stream()))
+				.containsExactly("east");
+	}
+
 	@Test
 	public void metricWithSpaceInTagValue() {
 		this.registry.counter("counter", "key", "a space").increment(2);