Add Resource, constantLabels and builder for java example

Author: mayurkale22

metrics/Gauge.md

@@ -8,13 +8,14 @@ The `Gauge` values can be negative. This document describes the key types and th
 The value that is published for gauges is an instantaneous measurement of an `int64` or `double` value. This API is useful when you want to manually increase and decrease values as per service requirements.
 
 The following general operations MUST be provided by the API:
-* Defining a `name`, `description`, `unit`, `labelKeys` and `constantLabels` which are fixed labels that always apply to a gauge. This should give back the gauge object to get or create time series, remove time series and clear all time series.
+* Defining a `name`, `description`, `unit`, `labelKeys`, `resource` and `constantLabels` which are fixed labels that always apply to a gauge. This should give back the gauge object to get or create time series, remove time series and clear all time series.
 	* `name`: a string describing the name of the metric, e.g. "vm_cpu_cycles" or "queue_size". Names MUST be unique within the library. It is recommended to use names compatible with the intended end usage.
 	* `description`: a string describing the metric, e.g."Virtual cycles executed on VM".
-	* `unit`: a string describing the unit used for the metric. Follows the format described by
+	* `unit`: a string describing the unit used for the metric (default set to "1"). Follows the format described by
 [Unified Code for Units of Measure](http://unitsofmeasure.org/ucum.html).
 	* `labelKeys`: the list of the label keys to track different types of metric.
-	* `constantLabels`: the map of label keys and label values.
+	* `constantLabels`: the map of label keys and label values. The keys in `labelKeys` should not be the same as `constantLabels`'s keys.
+	* `resource`: the optional associated monitored resource information.
 * Add a new time series with label values, which returns a `Point` (which is part of the `TimeSeries`). Each point represents an instantaneous measurement of a varying gauge value. Each Gauge Metric has one or more time series for a single metric.
 	* `labelValues`: the list of label values. The number of label values must be the same to that of the label keys.
 * The `Point` class should provide functionalities to manually increment/decrement values. Example: `add(long amt)`, `set(long value)`.
@@ -29,8 +30,14 @@ private static final MetricRegistry metricRegistry = Metrics.getMetricRegistry()
 
 List<LabelKey> labelKeys = Arrays.asList(LabelKey.create("key1", "description"));
 List<LabelValue> labelValues = Arrays.asList(LabelValue.create("queue1"));
+LabelKey constantLabelKey = LabelKey.create("hostname", "hostname");
+LabelValue constantLabelValue = LabelValue.create("localhost");
 
-LongGauge gauge = metricRegistry.addLongGauge("queue_size", "The number of jobs", "1", labelKeys);
+Map<LabelKey, LabelValue> constantLabels = Collections.singletonMap(constantLabelKey, constantLabelValue);
+
+LongGauge gauge = metricRegistry.addLongGauge().toBuilder()
+    .setName("queue_size").setDescription("The number of jobs")
+    .setLabelKeys(labelKeys).setConstantLabels(constantLabels).build();
 LongPoint point = gauge.getOrCreateTimeSeries(labelValues);
 
 void doSomeWork() {
@@ -44,16 +51,17 @@ It is recommended to keep a reference of a point for manual operations instead o
 The value that is published for gauges is an instantaneous measurement of an `int64` or `double` value. This gauge is self sufficient once created, so users should never need to interact with it. The value of the gauge is observed from the `object` and a `callback function`. The callback function is invoked whenever metrics are collected, meaning the reported value is up-to-date. The implementation should keep a `WeakReference` to the object and it is the user's responsibility to manage the lifetime of the object.
 
 The following general operations MUST be provided by the API:
-* Defining a `name`, `description`, `unit`, `labelKeys` and `constantLabels` which are fixed labels that always apply to a gauge. This should give back gauge object to add new time series, remove time series and clear all time series.
+* Defining a `name`, `description`, `unit`, `labelKeys`, `resource` and `constantLabels` which are fixed labels that always apply to a gauge. This should give back gauge object to add new time series, remove time series and clear all time series.
 	* `name`: a string describing the name of the metric, e.g. "vm_cpu_cycles". Names MUST be unique within the library. It is recommended to use names compatible with the intended end usage.
 	* `description`: a string describing the metric, e.g."Virtual cycles executed on VM".
-	* `unit`: a string describing the unit used for the metric. Follows the format described by
+	* `unit`: a string describing the unit used for the metric (default set to "1"). Follows the format described by
 [Unified Code for Units of Measure](http://unitsofmeasure.org/ucum.html).
 	* `labelKeys`: the list of the label keys to track different types of metric.
-	* `constantLabels`: the map of label keys and label values.
+	* `constantLabels`: the map of label keys and label values. The keys in `labelKeys` should not be the same as `constantLabels`'s keys.
+	* `resource`: the optional associated monitored resource information.
 * Add a new time series with label values, an `object` and a `callback function`. The number of label values must be the same to that of the label keys.
 	* `labelValues`: the list of label values. The number of label values must be the same to that of the label keys.
-	* `obj`: the state object from which the function derives a measurement.
+	* `object`: the state object from which the function derives a measurement.
 	* `function`: the callback function to be called.
 * Remove a single time series from the gauge metric, if it is present.
 	* `labelValues`: the list of label values.
@@ -65,10 +73,14 @@ private static final MetricRegistry metricRegistry = Metrics.getMetricRegistry()
 
 List<LabelKey> labelKeys = Arrays.asList(LabelKey.create("key1", "description"));
 List<LabelValue> labelValues = Arrays.asList(LabelValue.create("value1"));
+LabelKey constantLabelKey = LabelKey.create("hostname", "hostname");
+LabelValue constantLabelValue = LabelValue.create("localhost");
+
+Map<LabelKey, LabelValue> constantLabels = Collections.singletonMap(constantLabelKey, constantLabelValue);
 
-DerivedDoubleGauge gauge = metricRegistry.addDerivedDoubleGauge(
-    "vm_cpu_cycles", "Virtual cycles executed on VM", "1", labelKeys);
-CpuInfo cpuInfo = new CpuInfo();
+DerivedDoubleGauge gauge = metricRegistry.addDerivedDoubleGauge().toBuilder()
+    .setName("vm_cpu_cycles").setDescription("Virtual cycles executed on VM")
+    .setLabelKeys(labelKeys).setConstantLabels(constantLabels).build();
 
 gauge.createTimeSeries(labelValues, cpuInfo,
       new ToDoubleFunction<CpuInfo>() {