Add sample for MultiGauge (#4618)

samples/micrometer-samples-core/src/main/java/io/micrometer/core/samples/MultiGaugeSample.java

@@ -0,0 +1,87 @@
+/*
+ * Copyright 2024 VMware, Inc.
+ *
+ * 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.core.samples;
+
+import io.micrometer.core.instrument.MultiGauge;
+import io.micrometer.core.instrument.MultiGauge.Row;
+import io.micrometer.core.instrument.Tags;
+import io.micrometer.core.instrument.simple.SimpleMeterRegistry;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class MultiGaugeSample {
+
+    public static void main(String[] args) {
+        // MeterRegistry registry = SampleConfig.myMonitoringSystem();
+        SimpleMeterRegistry registry = new SimpleMeterRegistry();
+
+        MultiGauge temperatures = MultiGauge.builder("temperatures")
+            .tag("home", "little-house")
+            .description("The temperature by room")
+            .baseUnit("celsius")
+            .register(registry);
+
+        // @formatter:off
+        for (int i = 0; i < 3; i++) {
+            temperatures.register(
+                fetchTemperatures().stream()
+                    .map(record -> Row.of(Tags.of("room", record.getRoom().name()), record.getTemperature()))
+                    .collect(Collectors.toList()),
+                true // whether to overwrite the previous value or only record it once
+            );
+
+            System.out.println("---");
+            System.out.println(registry.getMetersAsString());
+        }
+        // @formatter:on
+    }
+
+    private static List<TemperatureRecord> fetchTemperatures() {
+        return Arrays.stream(Room.values())
+            .map(room -> new TemperatureRecord(room, Math.random() * 3 + 20))
+            .collect(Collectors.toList());
+    }
+
+    private enum Room {
+
+        LIVING_ROOM, BEDROOM, KITCHEN
+
+    }
+
+    private static class TemperatureRecord {
+
+        private final Room room;
+
+        private final double temperature;
+
+        private TemperatureRecord(Room room, double temperature) {
+            this.room = room;
+            this.temperature = temperature;
+        }
+
+        public Room getRoom() {
+            return room;
+        }
+
+        public double getTemperature() {
+            return temperature;
+        }
+
+    }
+
+}