[FLINK-20533][datadog] Encapsulate metric meta data

This allows us to use the 'MetricMetaData' container for histograms later on, which will not directly extend 'DMetric'.

flink-metrics/flink-metrics-datadog/src/main/java/org/apache/flink/metrics/datadog/DCounter.java

@@ -32,7 +32,7 @@ public class DCounter extends DMetric {
 	private long currentReportCount = 0;
 
 	public DCounter(Counter c, String metricName, String host, List<String> tags, Clock clock) {
-		super(MetricType.count, metricName, host, tags, clock);
+		super(new MetricMetaData(MetricType.count, metricName, host, tags, clock));
 		counter = c;
 	}
 

flink-metrics/flink-metrics-datadog/src/main/java/org/apache/flink/metrics/datadog/DGauge.java

@@ -29,7 +29,7 @@ public class DGauge extends DMetric {
 	private final Gauge<Number> gauge;
 
 	public DGauge(Gauge<Number> g, String metricName, String host, List<String> tags, Clock clock) {
-		super(MetricType.gauge, metricName, host, tags, clock);
+		super(new MetricMetaData(MetricType.gauge, metricName, host, tags, clock));
 		gauge = g;
 	}
 

flink-metrics/flink-metrics-datadog/src/main/java/org/apache/flink/metrics/datadog/DMeter.java

@@ -31,7 +31,7 @@ public class DMeter extends DMetric {
 	private final Meter meter;
 
 	public DMeter(Meter m, String metricName, String host, List<String> tags, Clock clock) {
-		super(MetricType.gauge, metricName, host, tags, clock);
+		super(new MetricMetaData(MetricType.gauge, metricName, host, tags, clock));
 		meter = m;
 	}
 

flink-metrics/flink-metrics-datadog/src/main/java/org/apache/flink/metrics/datadog/DMetric.java

@@ -44,45 +44,37 @@ public abstract class DMetric {
 	@VisibleForTesting
 	static final String FIELD_NAME_POINTS = "points";
 
-	private final String metricName;
-	private final MetricType type;
-	private final String host;
-	private final List<String> tags;
-	private final Clock clock;
-
-	public DMetric(MetricType metricType, String metricName, String host, List<String> tags, Clock clock) {
-		this.type = metricType;
-		this.metricName = metricName;
-		this.host = host;
-		this.tags = tags;
-		this.clock = clock;
+	private final MetricMetaData metaData;
+
+	public DMetric(MetricMetaData metaData) {
+		this.metaData = metaData;
 	}
 
 	@JsonGetter(FIELD_NAME_TYPE)
 	public MetricType getType() {
-		return type;
+		return metaData.getType();
 	}
 
 	@JsonGetter(FIELD_NAME_METRIC)
 	public String getMetricName() {
-		return metricName;
+		return metaData.getMetricName();
 	}
 
 	@JsonGetter(FIELD_NAME_HOST)
 	public String getHost() {
-		return host;
+		return metaData.getHost();
 	}
 
 	@JsonGetter(FIELD_NAME_TAGS)
 	public List<String> getTags() {
-		return tags;
+		return metaData.getTags();
 	}
 
 	@JsonGetter(FIELD_NAME_POINTS)
 	public List<List<Number>> getPoints() {
 		// One single data point
 		List<Number> point = new ArrayList<>();
-		point.add(clock.getUnixEpochTimestamp());
+		point.add(metaData.getClock().getUnixEpochTimestamp());
 		point.add(getMetricValue());
 
 		List<List<Number>> points = new ArrayList<>();

flink-metrics/flink-metrics-datadog/src/main/java/org/apache/flink/metrics/datadog/MetricMetaData.java

@@ -0,0 +1,61 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.apache.flink.metrics.datadog;
+
+import java.util.List;
+
+/**
+ * All metadata associated with a given metric.
+ */
+public final class MetricMetaData {
+
+	private final String metricName;
+	private final MetricType type;
+	private final String host;
+	private final List<String> tags;
+	private final Clock clock;
+
+	public MetricMetaData(MetricType metricType, String metricName, String host, List<String> tags, Clock clock) {
+		this.type = metricType;
+		this.metricName = metricName;
+		this.host = host;
+		this.tags = tags;
+		this.clock = clock;
+	}
+
+	public MetricType getType() {
+		return type;
+	}
+
+	public String getMetricName() {
+		return metricName;
+	}
+
+	public String getHost() {
+		return host;
+	}
+
+	public List<String> getTags() {
+		return tags;
+	}
+
+	public Clock getClock() {
+		return clock;
+	}
+}