Add support for creating KeyValues from any iterable (#3503)

Add new `of` and `and` methods that allow `KeyValues` to be created
from any iterable.

Author: philwebb

micrometer-commons/src/main/java/io/micrometer/common/KeyValue.java

@@ -15,6 +15,7 @@
  */
 package io.micrometer.common;
 
+import java.util.function.Function;
 import java.util.function.Predicate;
 
 import io.micrometer.common.docs.KeyName;
@@ -57,6 +58,18 @@ static KeyValue of(KeyName keyName, String value) {
         return KeyValue.of(keyName.asString(), value);
     }
 
+    /**
+     * Creates a {@link KeyValue} for the given {@code element} by extracting a key and
+     * value from it.
+     * @param element the source element
+     * @param keyExtractor function to extract the key from the element
+     * @param valueExtractor function to extract the value from the element
+     * @return KeyValue
+     */
+    static <E> KeyValue of(E element, Function<E, String> keyExtractor, Function<E, String> valueExtractor) {
+        return KeyValue.of(keyExtractor.apply(element), valueExtractor.apply(element));
+    }
+
     /**
      * Creates a {@link KeyValue} for the given key and value and additionally validates
      * it with the {@link Predicate}.

micrometer-commons/src/main/java/io/micrometer/common/KeyValues.java

@@ -18,6 +18,7 @@
 import io.micrometer.common.lang.Nullable;
 
 import java.util.*;
+import java.util.function.Function;
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
@@ -106,6 +107,24 @@ public KeyValues and(@Nullable KeyValue... keyValues) {
         return new KeyValues(newKeyValues);
     }
 
+    /**
+     * Return a new {@code KeyValues} instance by merging this collection and the key
+     * values extracted from the given elements.
+     * @param elements the source elements
+     * @param keyExtractor function to extract the key from the element
+     * @param valueExtractor function to extract the value from the element
+     * @return a new {@code KeyValues} instance
+     */
+    public <E> KeyValues and(@Nullable Iterable<E> elements, Function<E, String> keyExtractor,
+            Function<E, String> valueExtractor) {
+        if (elements == null || !elements.iterator().hasNext()) {
+            return this;
+        }
+        Function<E, KeyValue> mapper = element -> KeyValue.of(element, keyExtractor, valueExtractor);
+        Iterable<KeyValue> keyValues = () -> StreamSupport.stream(elements.spliterator(), false).map(mapper).iterator();
+        return and(keyValues);
+    }
+
     /**
      * Return a new {@code KeyValues} instance by merging this collection and the
      * specified key values.
@@ -217,6 +236,19 @@ public static KeyValues concat(@Nullable Iterable<? extends KeyValue> keyValues,
         return KeyValues.of(keyValues).and(otherKeyValues);
     }
 
+    /**
+     * Return a new {@code KeyValues} instance containing key values extracted from the
+     * given elements.
+     * @param elements the source elements
+     * @param keyExtractor function to extract the key from the element
+     * @param valueExtractor function to extract the value from the element
+     * @return a new {@code KeyValues} instance
+     */
+    public static <E> KeyValues of(@Nullable Iterable<E> elements, Function<E, String> keyExtractor,
+            Function<E, String> valueExtractor) {
+        return empty().and(elements, keyExtractor, valueExtractor);
+    }
+
     /**
      * Return a new {@code KeyValues} instance containing key values constructed from the
      * specified source key values.

micrometer-commons/src/test/java/io/micrometer/common/KeyValuesTest.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2022 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
+ *
+ *      https://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 io.micrometer.common;
+
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link KeyValues}.
+ */
+class KeyValuesTest {
+
+    @Test
+    void ofExtractingFromElementsReturnsKeyValues() {
+        Map<String, String> map = Map.of("micrometer", "tracing", "can", "trace");
+        KeyValues keyValues = KeyValues.of(map.entrySet(), Map.Entry::getKey, Map.Entry::getValue);
+        assertThat(keyValues).containsExactlyInAnyOrder(KeyValue.of("micrometer", "tracing"),
+                KeyValue.of("can", "trace"));
+    }
+
+    @Test
+    void andExtractingFromElementsReturnsKeyValues() {
+        Map<String, String> map = Map.of("micrometer", "tracing", "can", "trace");
+        KeyValues keyValues = KeyValues.of("no", "way").and(map.entrySet(), Map.Entry::getKey, Map.Entry::getValue);
+        assertThat(keyValues).containsExactlyInAnyOrder(KeyValue.of("no", "way"), KeyValue.of("micrometer", "tracing"),
+                KeyValue.of("can", "trace"));
+    }
+
+}