Add dropwizard contrib (#1423)

* Add dropwizard metrics producer

* Use Summary Type

* Fix reviews

* Fix reviews

10 files changed, 921 insertions, 0 deletions

diff --git a/all/build.gradle b/all/build.gradle
index e3a0c4c6..83ffb69e 100644
--- a/all/build.gradle
+++ b/all/build.gradle
@@ -8,6 +8,7 @@ def subprojects = [
         project(':opencensus-testing'),
         project(':opencensus-contrib-agent'),
         project(':opencensus-contrib-appengine-standard-util'),
+        project(':opencensus-contrib-dropwizard'),
         project(':opencensus-contrib-exemplar-util'),
         project(':opencensus-contrib-grpc-util'),
         project(':opencensus-contrib-grpc-metrics'),
@@ -34,6 +35,7 @@ def subprojects_javadoc = [
         project(':opencensus-testing'),
         project(':opencensus-contrib-agent'),
         project(':opencensus-contrib-appengine-standard-util'),
+        project(':opencensus-contrib-dropwizard'),
         project(':opencensus-contrib-exemplar-util'),
         project(':opencensus-contrib-grpc-util'),
         project(':opencensus-contrib-grpc-metrics'),
diff --git a/build.gradle b/build.gradle
index 9ecd7b90..abf2413b 100644
--- a/build.gradle
+++ b/build.gradle
@@ -168,6 +168,7 @@ subprojects {
         zipkinReporterVersion = '2.3.2'
         jaegerReporterVersion = '0.27.0'
         opencensusProtoVersion = '0.0.2'
+        dropwizardVersion = '3.1.2'
 
         libraries = [
                 appengine_api: "com.google.appengine:appengine-api-1.0-sdk:${appengineVersion}",
@@ -208,6 +209,7 @@ subprojects {
                 mockito: 'org.mockito:mockito-core:1.9.5',
                 spring_test: "org.springframework:spring-test:${springVersion}",
                 truth: 'com.google.truth:truth:0.30',
+                dropwizard: "io.dropwizard.metrics:metrics-core:${dropwizardVersion}",
         ]
     }
 
@@ -416,6 +418,7 @@ subprojects {
         name in ['opencensus-api',
                  'opencensus-contrib-agent',
                  'opencensus-contrib-appengine-standard-util',
+                 'opencensus-contrib-dropwizard',
                  'opencensus-contrib-exemplar-util',
                  'opencensus-contrib-grpc-metrics',
                  'opencensus-contrib-grpc-util',
diff --git a/buildscripts/import-control.xml b/buildscripts/import-control.xml
index 002820d8..be93cd9e 100644
--- a/buildscripts/import-control.xml
+++ b/buildscripts/import-control.xml
@@ -134,6 +134,13 @@ General guidelines on imports:
     <subpackage name="monitoredresource.util">
       <allow pkg="io.opencensus.contrib.monitoredresource.util"/>
     </subpackage>
+    <subpackage name="dropwizard">
+      <allow pkg="io.opencensus.contrib.dropwizard"/>
+      <allow pkg="io.opencensus.metrics"/>
+      <allow pkg="io.opencensus.implcore"/>
+      <allow pkg="io.opencensus.internal"/>
+      <allow pkg="com.codahale.metrics"/>
+    </subpackage>
   </subpackage>
   <subpackage name="exporter">
     <allow pkg="com.google.common"/>
diff --git a/contrib/dropwizard/README.md b/contrib/dropwizard/README.md
new file mode 100644
index 00000000..395c303f
--- /dev/null
+++ b/contrib/dropwizard/README.md
@@ -0,0 +1,120 @@
+# OpenCensus DropWizard Util for Java
+
+The *OpenCensus DropWizard Util for Java* provides an easy way to translate Dropwizard metrics to
+OpenCensus.
+
+## Quickstart
+
+### Prerequisites
+
+Assuming, you already have both the OpenCensus and Dropwizard client libraries setup and working
+inside your application.
+
+### Add the dependencies to your project
+
+For Maven add to your `pom.xml`:
+```xml
+<dependencies>
+  <dependency>
+    <groupId>io.opencensus</groupId>
+    <artifactId>opencensus-contrib-dropwizard</artifactId>
+    <version>0.17.0</version>
+  </dependency>
+</dependencies>
+```
+
+For Gradle add to your dependencies:
+```gradle
+compile 'io.opencensus:opencensus-dropwizard:0.17.0'
+```
+
+### And the following code:
+
+```java
+import java.util.Collections;
+
+public class YourClass {
+  // Create registry for Dropwizard metrics.
+  static final com.codahale.metrics.MetricRegistry codahaleRegistry =
+    new com.codahale.metrics.MetricRegistry();
+
+  // Create a Dropwizard counter.
+  static final com.codahale.metrics.Counter requests = codahaleRegistry.counter("requests");
+
+  public static void main(String[] args) {
+
+    // Increment the requests.
+    requests.inc();
+
+    // Hook the Dropwizard registry into the OpenCensus registry
+    // via the DropWizardMetrics metric producer.
+    io.opencensus.metrics.Metrics.getExportComponent().getMetricProducerManager().add(
+          new io.opencensus.contrib.dropwizard.DropWizardMetrics(
+            Collections.singletonList(codahaleRegistry)));
+
+  }
+}
+```
+
+## Translation to OpenCensus Metrics
+
+This section describes how each of the DropWizard metrics translate into OpenCensus metrics.
+
+### DropWizard Counters
+
+Given a DropWizard Counter with name `cache_evictions`, the following values are reported:
+
+* name: codahale_<initial_metric_name>_<initial_type> (ex: codahale_cache_evictions_counter)
+* description: Collected from Dropwizard (metric=<metric_name>, type=<class_name>)
+(ex: Collected from Dropwizard (metric=cache_evictions, type=com.codahale.metrics.Counter))
+* type: GAUGE_INT64
+* unit: 1
+
+Note: OpenCensus's CUMULATIVE_INT64 type represent monotonically increasing values. Since
+DropWizard Counter goes up/down, it make sense to report them as OpenCensus GAUGE_INT64.
+
+### DropWizard Gauges
+
+Given a DropWizard Gauge with name `line_requests`, the following values are reported:
+
+* name: codahale_<initial_metric_name>_<initial_type> (ex: codahale_line_requests_gauge)
+* description: Collected from Dropwizard (metric=<metric_name>, type=<class_name>)
+* type: GAUGE_INT64 or GAUGE_DOUBLE
+* unit: 1
+
+Note: For simplicity, OpenCensus uses GAUGE_DOUBLE type for any Number and GAUGE_INT64
+type for Boolean values.
+
+### DropWizard Meters
+
+Given a DropWizard Meter with name `get_requests`, the following values are reported:
+
+* name: codahale_<initial_metric_name>_<initial_type> (ex: codahale_get_requests_meter)
+* description: Collected from Dropwizard (metric=<metric_name>, type=<class_name>)
+* type: CUMULATIVE_INT64
+* unit: 1
+
+rate metrics:
+* name: codahale_<initial_metric_name>_<initial_type> (ex: codahale_get_requests_meter_rate)
+* description: Collected from Dropwizard (metric=<metric_name>, type=<class_name>)
+* type: GAUGE_DOUBLE
+* unit: "events/second"
+* labelkeys: rate (with 4 TimeSeries, one corresponding to each rate: mean_rate, m1_rate, 
+m5_rate m15_rate)
+
+### DropWizard Histograms
+
+Given a DropWizard Histogram with name `results`, the following values are reported:
+
+* name: codahale_<initial_metric_name>_<initial_type> (ex: codahale_results_histogram)
+* description: Collected from Dropwizard (metric=<metric_name>, type=<class_name>)
+* type: SUMMARY
+* unit: 1
+
+### DropWizard Timers
+
+Given a DropWizard Timer with name `requests`, the following values are reported:
+* name: codahale_<initial_metric_name>_<initial_type> (ex: codahale_requests_timer)
+* description: Collected from Dropwizard (metric=<metric_name>, type=<class_name>)
+* type: SUMMARY
+* unit: 1
diff --git a/contrib/dropwizard/build.gradle b/contrib/dropwizard/build.gradle
new file mode 100644
index 00000000..7da41cbe
--- /dev/null
+++ b/contrib/dropwizard/build.gradle
@@ -0,0 +1,17 @@
+description = 'OpenCensus dropwizard util'
+
+apply plugin: 'java'
+
+[compileJava, compileTestJava].each() {
+    it.sourceCompatibility = 1.7
+    it.targetCompatibility = 1.7
+}
+
+dependencies {
+    compile project(':opencensus-api'),
+            project(':opencensus-impl-core')
+
+    compile libraries.dropwizard
+
+    signature "org.codehaus.mojo.signature:java17:1.0@signature"
+}
diff --git a/contrib/dropwizard/src/main/java/io/opencensus/contrib/dropwizard/DropWizardMetrics.java b/contrib/dropwizard/src/main/java/io/opencensus/contrib/dropwizard/DropWizardMetrics.java
new file mode 100644
index 00000000..7cc52d3f
--- /dev/null
+++ b/contrib/dropwizard/src/main/java/io/opencensus/contrib/dropwizard/DropWizardMetrics.java
@@ -0,0 +1,330 @@
+/*
+ * Copyright 2018, OpenCensus 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
+ *
+ *     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 io.opencensus.contrib.dropwizard;
+
+import com.codahale.metrics.Counter;
+import com.codahale.metrics.Gauge;
+import com.codahale.metrics.Histogram;
+import com.codahale.metrics.Meter;
+import com.codahale.metrics.Timer;
+import io.opencensus.common.Clock;
+import io.opencensus.common.Timestamp;
+import io.opencensus.implcore.common.MillisClock;
+import io.opencensus.internal.DefaultVisibilityForTesting;
+import io.opencensus.internal.Utils;
+import io.opencensus.metrics.LabelKey;
+import io.opencensus.metrics.LabelValue;
+import io.opencensus.metrics.export.Metric;
+import io.opencensus.metrics.export.MetricDescriptor;
+import io.opencensus.metrics.export.MetricDescriptor.Type;
+import io.opencensus.metrics.export.MetricProducer;
+import io.opencensus.metrics.export.Point;
+import io.opencensus.metrics.export.Summary;
+import io.opencensus.metrics.export.Summary.Snapshot;
+import io.opencensus.metrics.export.Summary.Snapshot.ValueAtPercentile;
+import io.opencensus.metrics.export.TimeSeries;
+import io.opencensus.metrics.export.Value;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map.Entry;
+import javax.annotation.Nullable;
+
+/**
+ * Collects DropWizard metrics from a list {@link com.codahale.metrics.MetricRegistry}s.
+ *
+ * <p>A {@link io.opencensus.metrics.export.MetricProducer} that wraps a DropWizardMetrics.
+ *
+ * @since 0.17
+ */
+public class DropWizardMetrics extends MetricProducer {
+
+  @DefaultVisibilityForTesting static final String DEFAULT_UNIT = "1";
+
+  @DefaultVisibilityForTesting
+  static final List<LabelKey> RATE_LABEL_KEY =
+      Collections.singletonList(LabelKey.create("rate", "measures the rate of events over time"));
+
+  @DefaultVisibilityForTesting
+  static final List<LabelValue> RATE_MEAN_LABEL_VALUE =
+      Collections.singletonList(LabelValue.create("mean_rate"));
+
+  @DefaultVisibilityForTesting
+  static final List<LabelValue> RATE_ONE_MINUTE_LABEL_VALUE =
+      Collections.singletonList(LabelValue.create("m1_rate"));
+
+  @DefaultVisibilityForTesting
+  static final List<LabelValue> RATE_FIVE_MINUTE_LABEL_VALUE =
+      Collections.singletonList(LabelValue.create("m5_rate"));
+
+  @DefaultVisibilityForTesting
+  static final List<LabelValue> RATE_FIFTEEN_MINUTE_LABEL_VALUE =
+      Collections.singletonList(LabelValue.create("m15_rate"));
+
+  private final List<com.codahale.metrics.MetricRegistry> metricRegistryList;
+  private final Clock clock;
+  private final Timestamp cumulativeStartTimestamp;
+
+  /**
+   * Hook the Dropwizard registry into the OpenCensus registry.
+   *
+   * @param metricRegistryList a list of {@link com.codahale.metrics.MetricRegistry}s.
+   * @since 0.17
+   */
+  public DropWizardMetrics(List<com.codahale.metrics.MetricRegistry> metricRegistryList) {
+    Utils.checkNotNull(metricRegistryList, "metricRegistryList");
+    Utils.checkListElementNotNull(metricRegistryList, "metricRegistryList");
+    this.metricRegistryList = metricRegistryList;
+    clock = MillisClock.getInstance();
+    cumulativeStartTimestamp = clock.now();
+  }
+
+  /**
+   * Returns a {@code Metric} collected from {@link Gauge}.
+   *
+   * @param dropwizardName the metric name.
+   * @param gauge the gauge object to collect.
+   * @return a {@code Metric}.
+   */
+  @SuppressWarnings("rawtypes")
+  private @Nullable Metric collectGauge(String dropwizardName, Gauge gauge) {
+    String metricName = DropWizardUtils.generateFullMetricName(dropwizardName, "gauge");
+    String metricDescription = DropWizardUtils.generateFullMetricDescription(dropwizardName, gauge);
+
+    // Figure out which gauge instance and call the right method to get value
+    Type type;
+    Value value;
+
+    Object obj = gauge.getValue();
+    if (obj instanceof Number) {
+      type = Type.GAUGE_DOUBLE;
+      value = Value.doubleValue(((Number) obj).doubleValue());
+    } else if (obj instanceof Boolean) {
+      type = Type.GAUGE_INT64;
+      value = Value.longValue(((Boolean) obj) ? 1 : 0);
+    } else {
+      // Ignoring Gauge (gauge.getKey()) with unhandled type.
+      return null;
+    }
+
+    MetricDescriptor metricDescriptor =
+        MetricDescriptor.create(
+            metricName, metricDescription, DEFAULT_UNIT, type, Collections.<LabelKey>emptyList());
+    TimeSeries timeSeries =
+        TimeSeries.create(
+            Collections.<LabelValue>emptyList(),
+            Collections.singletonList(Point.create(value, clock.now())),
+            null);
+    return Metric.create(metricDescriptor, Collections.singletonList(timeSeries));
+  }
+
+  /**
+   * Returns a {@code Metric} collected from {@link Counter}.
+   *
+   * @param dropwizardName the metric name.
+   * @param counter the counter object to collect.
+   * @return a {@code Metric}.
+   */
+  private Metric collectCounter(String dropwizardName, Counter counter) {
+    String metricName = DropWizardUtils.generateFullMetricName(dropwizardName, "counter");
+    String metricDescription =
+        DropWizardUtils.generateFullMetricDescription(dropwizardName, counter);
+
+    MetricDescriptor metricDescriptor =
+        MetricDescriptor.create(
+            metricName,
+            metricDescription,
+            DEFAULT_UNIT,
+            Type.GAUGE_INT64,
+            Collections.<LabelKey>emptyList());
+    TimeSeries timeSeries =
+        TimeSeries.create(
+            Collections.<LabelValue>emptyList(),
+            Collections.singletonList(
+                Point.create(Value.longValue(counter.getCount()), clock.now())),
+            null);
+    return Metric.create(metricDescriptor, Collections.singletonList(timeSeries));
+  }
+
+  /**
+   * Returns a list of {@link Metric}s collected from {@link Meter}.
+   *
+   * @param dropwizardName the metric name.
+   * @param meter the meter object to collect
+   * @return a list of {@link Metric}s.
+   */
+  private List<Metric> collectMeter(String dropwizardName, Meter meter) {
+    String metricName = DropWizardUtils.generateFullMetricName(dropwizardName, "meter");
+    String metricDescription = DropWizardUtils.generateFullMetricDescription(dropwizardName, meter);
+
+    MetricDescriptor countMetricDescriptor =
+        MetricDescriptor.create(
+            metricName,
+            metricDescription,
+            DEFAULT_UNIT,
+            Type.CUMULATIVE_INT64,
+            Collections.<LabelKey>emptyList());
+    TimeSeries countTimeSeries =
+        TimeSeries.create(
+            Collections.<LabelValue>emptyList(),
+            Collections.singletonList(Point.create(Value.longValue(meter.getCount()), clock.now())),
+            null);
+
+    // Collect rate related metric
+    metricName = DropWizardUtils.generateFullMetricName(dropwizardName, "meter_rate");
+    metricDescription = DropWizardUtils.generateFullMetricDescription(dropwizardName, meter);
+
+    MetricDescriptor rateMetricDescriptor =
+        MetricDescriptor.create(
+            metricName, metricDescription, "events/second", Type.GAUGE_DOUBLE, RATE_LABEL_KEY);
+
+    List<TimeSeries> timeSeriesList =
+        Arrays.asList(
+            TimeSeries.create(
+                RATE_MEAN_LABEL_VALUE,
+                Collections.singletonList(
+                    Point.create(Value.doubleValue(meter.getMeanRate()), clock.now())),
+                null),
+            TimeSeries.create(
+                RATE_ONE_MINUTE_LABEL_VALUE,
+                Collections.singletonList(
+                    Point.create(Value.doubleValue(meter.getOneMinuteRate()), clock.now())),
+                null),
+            TimeSeries.create(
+                RATE_FIVE_MINUTE_LABEL_VALUE,
+                Collections.singletonList(
+                    Point.create(Value.doubleValue(meter.getFiveMinuteRate()), clock.now())),
+                null),
+            TimeSeries.create(
+                RATE_FIFTEEN_MINUTE_LABEL_VALUE,
+                Collections.singletonList(
+                    Point.create(Value.doubleValue(meter.getFifteenMinuteRate()), clock.now())),
+                null));
+
+    return Collections.unmodifiableList(
+        Arrays.asList(
+            Metric.create(countMetricDescriptor, Collections.singletonList(countTimeSeries)),
+            Metric.create(rateMetricDescriptor, Collections.unmodifiableList(timeSeriesList))));
+  }
+
+  /**
+   * Returns a {@code Metric} collected from {@link Histogram}.
+   *
+   * @param dropwizardName the metric name.
+   * @param histogram the histogram object to collect
+   * @return a {@code Metric}.
+   */
+  private Metric collectHistogram(String dropwizardName, Histogram histogram) {
+    String metricName = DropWizardUtils.generateFullMetricName(dropwizardName, "histogram");
+    String metricDescription =
+        DropWizardUtils.generateFullMetricDescription(dropwizardName, histogram);
+    return collectSnapshotAndCount(
+        metricName, metricDescription, histogram.getSnapshot(), histogram.getCount());
+  }
+
+  /**
+   * Returns a {@code Metric} collected from {@link Timer}.
+   *
+   * @param dropwizardName the metric name.
+   * @param timer the timer object to collect
+   * @return a {@code Metric}.
+   */
+  private Metric collectTimer(String dropwizardName, Timer timer) {
+    String metricName = DropWizardUtils.generateFullMetricName(dropwizardName, "timer");
+    String metricDescription = DropWizardUtils.generateFullMetricDescription(dropwizardName, timer);
+    return collectSnapshotAndCount(
+        metricName, metricDescription, timer.getSnapshot(), timer.getCount());
+  }
+
+  /**
+   * Returns a {@code Metric} collected from {@link Snapshot}.
+   *
+   * @param metricName the metric name.
+   * @param metricDescription the metric description.
+   * @param codahaleSnapshot the snapshot object to collect
+   * @param count the value or count
+   * @return a {@code Metric}.
+   */
+  private Metric collectSnapshotAndCount(
+      String metricName,
+      String metricDescription,
+      com.codahale.metrics.Snapshot codahaleSnapshot,
+      long count) {
+    List<ValueAtPercentile> valueAtPercentiles =
+        Arrays.asList(
+            ValueAtPercentile.create(50.0, codahaleSnapshot.getMedian()),
+            ValueAtPercentile.create(75.0, codahaleSnapshot.get75thPercentile()),
+            ValueAtPercentile.create(98.0, codahaleSnapshot.get98thPercentile()),
+            ValueAtPercentile.create(99.0, codahaleSnapshot.get99thPercentile()),
+            ValueAtPercentile.create(99.9, codahaleSnapshot.get999thPercentile()));
+
+    Snapshot snapshot = Snapshot.create((long) codahaleSnapshot.size(), 0.0, valueAtPercentiles);
+    Point point =
+        Point.create(Value.summaryValue(Summary.create(count, 0.0, snapshot)), clock.now());
+
+    // TODO(mayurkale): OPTIMIZATION: Cache the MetricDescriptor objects.
+    MetricDescriptor metricDescriptor =
+        MetricDescriptor.create(
+            metricName,
+            metricDescription,
+            DEFAULT_UNIT,
+            Type.SUMMARY,
+            Collections.<LabelKey>emptyList());
+    TimeSeries timeSeries =
+        TimeSeries.create(
+            Collections.<LabelValue>emptyList(),
+            Collections.singletonList(point),
+            cumulativeStartTimestamp);
+
+    return Metric.create(metricDescriptor, Collections.singletonList(timeSeries));
+  }
+
+  @Override
+  @SuppressWarnings("rawtypes")
+  public Collection<Metric> getMetrics() {
+    ArrayList<Metric> metrics = new ArrayList<Metric>();
+
+    for (com.codahale.metrics.MetricRegistry metricRegistry : metricRegistryList) {
+      for (Entry<String, Counter> counterEntry : metricRegistry.getCounters().entrySet()) {
+        metrics.add(collectCounter(counterEntry.getKey(), counterEntry.getValue()));
+      }
+
+      for (Entry<String, Gauge> gaugeEntry : metricRegistry.getGauges().entrySet()) {
+        Metric metric = collectGauge(gaugeEntry.getKey(), gaugeEntry.getValue());
+        if (metric != null) {
+          metrics.add(metric);
+        }
+      }
+
+      for (Entry<String, Meter> counterEntry : metricRegistry.getMeters().entrySet()) {
+        metrics.addAll(collectMeter(counterEntry.getKey(), counterEntry.getValue()));
+      }
+
+      for (Entry<String, Histogram> counterEntry : metricRegistry.getHistograms().entrySet()) {
+        metrics.add(collectHistogram(counterEntry.getKey(), counterEntry.getValue()));
+      }
+
+      for (Entry<String, Timer> counterEntry : metricRegistry.getTimers().entrySet()) {
+        metrics.add(collectTimer(counterEntry.getKey(), counterEntry.getValue()));
+      }
+    }
+
+    return metrics;
+  }
+}
diff --git a/contrib/dropwizard/src/main/java/io/opencensus/contrib/dropwizard/DropWizardUtils.java b/contrib/dropwizard/src/main/java/io/opencensus/contrib/dropwizard/DropWizardUtils.java
new file mode 100644
index 00000000..372e5c60
--- /dev/null
+++ b/contrib/dropwizard/src/main/java/io/opencensus/contrib/dropwizard/DropWizardUtils.java
@@ -0,0 +1,55 @@
+/*
+ * Copyright 2018, OpenCensus 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
+ *
+ *     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 io.opencensus.contrib.dropwizard;
+
+import com.codahale.metrics.Metric;
+
+/** Util methods for generating the metric name(unique) and description. */
+final class DropWizardUtils {
+  private static final String SOURCE = "codahale";
+  private static final char DELIMITER = '_';
+
+  /**
+   * Returns the metric name.
+   *
+   * @param name the initial metric name
+   * @param type the initial type of the metric.
+   * @return a string the unique metric name
+   */
+  static String generateFullMetricName(String name, String type) {
+    return SOURCE + DELIMITER + name + DELIMITER + type;
+  }
+
+  /**
+   * Returns the metric description.
+   *
+   * @param metricName the initial metric name
+   * @param metric the codahale metric class.
+   * @return a String the custom metric description
+   */
+  static String generateFullMetricDescription(String metricName, Metric metric) {
+    return "Collected from "
+        + SOURCE
+        + " (metric="
+        + metricName
+        + ", type="
+        + metric.getClass().getName()
+        + ")";
+  }
+
+  private DropWizardUtils() {}
+}
diff --git a/contrib/dropwizard/src/test/java/io/opencensus/contrib/dropwizard/DropWizardMetricsTest.java b/contrib/dropwizard/src/test/java/io/opencensus/contrib/dropwizard/DropWizardMetricsTest.java
new file mode 100644
index 00000000..f7304ceb
--- /dev/null
+++ b/contrib/dropwizard/src/test/java/io/opencensus/contrib/dropwizard/DropWizardMetricsTest.java
@@ -0,0 +1,344 @@
+/*
+ * Copyright 2018, OpenCensus 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
+ *
+ *     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 io.opencensus.contrib.dropwizard;
+
+import static com.google.common.truth.Truth.assertThat;
+import static io.opencensus.contrib.dropwizard.DropWizardMetrics.DEFAULT_UNIT;
+import static io.opencensus.contrib.dropwizard.DropWizardMetrics.RATE_FIFTEEN_MINUTE_LABEL_VALUE;
+import static io.opencensus.contrib.dropwizard.DropWizardMetrics.RATE_FIVE_MINUTE_LABEL_VALUE;
+import static io.opencensus.contrib.dropwizard.DropWizardMetrics.RATE_LABEL_KEY;
+import static io.opencensus.contrib.dropwizard.DropWizardMetrics.RATE_MEAN_LABEL_VALUE;
+import static io.opencensus.contrib.dropwizard.DropWizardMetrics.RATE_ONE_MINUTE_LABEL_VALUE;
+
+import com.codahale.metrics.Counter;
+import com.codahale.metrics.Gauge;
+import com.codahale.metrics.Histogram;
+import com.codahale.metrics.Meter;
+import com.codahale.metrics.Timer;
+import io.opencensus.common.Timestamp;
+import io.opencensus.metrics.LabelKey;
+import io.opencensus.metrics.export.Metric;
+import io.opencensus.metrics.export.MetricDescriptor;
+import io.opencensus.metrics.export.MetricDescriptor.Type;
+import io.opencensus.metrics.export.Summary;
+import io.opencensus.metrics.export.Summary.Snapshot;
+import io.opencensus.metrics.export.Summary.Snapshot.ValueAtPercentile;
+import io.opencensus.metrics.export.Value;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Unit tests for {@link DropWizardMetrics}. */
+@RunWith(JUnit4.class)
+public class DropWizardMetricsTest {
+
+  private com.codahale.metrics.MetricRegistry metricRegistry;
+  DropWizardMetrics dropWizardMetrics;
+
+  @Before
+  public void setUp() throws Exception {
+    metricRegistry = new com.codahale.metrics.MetricRegistry();
+    dropWizardMetrics = new DropWizardMetrics(Collections.singletonList((metricRegistry)));
+  }
+
+  @Test
+  public void collect() throws InterruptedException {
+
+    // create dropwizard metrics
+    Counter evictions = metricRegistry.counter("cache_evictions");
+    evictions.inc();
+    evictions.inc(3);
+    evictions.dec();
+    evictions.dec(2);
+
+    Gauge<Integer> integerGauge =
+        new Gauge<Integer>() {
+          @Override
+          public Integer getValue() {
+            return 1234;
+          }
+        };
+    metricRegistry.register("integer_gauge", integerGauge);
+
+    Gauge<Double> doubleGauge =
+        new Gauge<Double>() {
+          @Override
+          public Double getValue() {
+            return 1.234D;
+          }
+        };
+    metricRegistry.register("double_gauge", doubleGauge);
+
+    Gauge<Long> longGauge =
+        new Gauge<Long>() {
+          @Override
+          public Long getValue() {
+            return 1234L;
+          }
+        };
+    metricRegistry.register("long_gauge", longGauge);
+
+    Gauge<Float> floatGauge =
+        new Gauge<Float>() {
+          @Override
+          public Float getValue() {
+            return 0.1234F;
+          }
+        };
+    metricRegistry.register("float_gauge", floatGauge);
+
+    Gauge<Boolean> boolGauge =
+        new Gauge<Boolean>() {
+          @Override
+          public Boolean getValue() {
+            return Boolean.TRUE;
+          }
+        };
+    metricRegistry.register("boolean_gauge", boolGauge);
+
+    Meter getRequests = metricRegistry.meter("get_requests");
+    getRequests.mark();
+    getRequests.mark();
+
+    Histogram resultCounts = metricRegistry.histogram("result");
+    resultCounts.update(200);
+
+    Timer timer = metricRegistry.timer("requests");
+    Timer.Context context = timer.time();
+    Thread.sleep(1L);
+    context.stop();
+
+    ArrayList<Metric> metrics = new ArrayList<Metric>(dropWizardMetrics.getMetrics());
+    assertThat(metrics.size()).isEqualTo(10);
+
+    assertThat(metrics.get(0).getMetricDescriptor())
+        .isEqualTo(
+            MetricDescriptor.create(
+                "codahale_cache_evictions_counter",
+                "Collected from codahale (metric=cache_evictions, "
+                    + "type=com.codahale.metrics.Counter)",
+                DEFAULT_UNIT,
+                Type.GAUGE_INT64,
+                Collections.<LabelKey>emptyList()));
+    assertThat(metrics.get(0).getTimeSeriesList().size()).isEqualTo(1);
+    assertThat(metrics.get(0).getTimeSeriesList().get(0).getLabelValues().size()).isEqualTo(0);
+    assertThat(metrics.get(0).getTimeSeriesList().get(0).getPoints().size()).isEqualTo(1);
+    assertThat(metrics.get(0).getTimeSeriesList().get(0).getPoints().get(0).getValue())
+        .isEqualTo(Value.longValue(1));
+    assertThat(metrics.get(0).getTimeSeriesList().get(0).getStartTimestamp()).isEqualTo(null);
+
+    assertThat(metrics.get(1).getMetricDescriptor())
+        .isEqualTo(
+            MetricDescriptor.create(
+                "codahale_boolean_gauge_gauge",
+                "Collected from codahale (metric=boolean_gauge, "
+                    + "type=io.opencensus.contrib.dropwizard.DropWizardMetricsTest$5)",
+                DEFAULT_UNIT,
+                Type.GAUGE_INT64,
+                Collections.<LabelKey>emptyList()));
+    assertThat(metrics.get(1).getTimeSeriesList().size()).isEqualTo(1);
+    assertThat(metrics.get(1).getTimeSeriesList().get(0).getLabelValues().size()).isEqualTo(0);
+    assertThat(metrics.get(1).getTimeSeriesList().get(0).getPoints().size()).isEqualTo(1);
+    assertThat(metrics.get(1).getTimeSeriesList().get(0).getPoints().get(0).getValue())
+        .isEqualTo(Value.longValue(1));
+    assertThat(metrics.get(1).getTimeSeriesList().get(0).getStartTimestamp()).isEqualTo(null);
+
+    assertThat(metrics.get(2).getMetricDescriptor())
+        .isEqualTo(
+            MetricDescriptor.create(
+                "codahale_double_gauge_gauge",
+                "Collected from codahale (metric=double_gauge, "
+                    + "type=io.opencensus.contrib.dropwizard.DropWizardMetricsTest$2)",
+                DEFAULT_UNIT,
+                Type.GAUGE_DOUBLE,
+                Collections.<LabelKey>emptyList()));
+    assertThat(metrics.get(2).getTimeSeriesList().size()).isEqualTo(1);
+    assertThat(metrics.get(2).getTimeSeriesList().get(0).getLabelValues().size()).isEqualTo(0);
+    assertThat(metrics.get(2).getTimeSeriesList().get(0).getPoints().size()).isEqualTo(1);
+    assertThat(metrics.get(2).getTimeSeriesList().get(0).getPoints().get(0).getValue())
+        .isEqualTo(Value.doubleValue(1.234));
+    assertThat(metrics.get(2).getTimeSeriesList().get(0).getStartTimestamp()).isEqualTo(null);
+
+    assertThat(metrics.get(3).getMetricDescriptor())
+        .isEqualTo(
+            MetricDescriptor.create(
+                "codahale_float_gauge_gauge",
+                "Collected from codahale (metric=float_gauge, "
+                    + "type=io.opencensus.contrib.dropwizard.DropWizardMetricsTest$4)",
+                DEFAULT_UNIT,
+                Type.GAUGE_DOUBLE,
+                Collections.<LabelKey>emptyList()));
+    assertThat(metrics.get(3).getTimeSeriesList().size()).isEqualTo(1);
+    assertThat(metrics.get(3).getTimeSeriesList().get(0).getLabelValues().size()).isEqualTo(0);
+    assertThat(metrics.get(3).getTimeSeriesList().get(0).getPoints().size()).isEqualTo(1);
+    assertThat(metrics.get(3).getTimeSeriesList().get(0).getPoints().get(0).getValue())
+        .isEqualTo(Value.doubleValue(0.1234000027179718));
+    assertThat(metrics.get(3).getTimeSeriesList().get(0).getStartTimestamp()).isEqualTo(null);
+
+    assertThat(metrics.get(4).getMetricDescriptor())
+        .isEqualTo(
+            MetricDescriptor.create(
+                "codahale_integer_gauge_gauge",
+                "Collected from codahale (metric=integer_gauge, "
+                    + "type=io.opencensus.contrib.dropwizard.DropWizardMetricsTest$1)",
+                DEFAULT_UNIT,
+                Type.GAUGE_DOUBLE,
+                Collections.<LabelKey>emptyList()));
+    assertThat(metrics.get(4).getTimeSeriesList().size()).isEqualTo(1);
+    assertThat(metrics.get(4).getTimeSeriesList().get(0).getLabelValues().size()).isEqualTo(0);
+    assertThat(metrics.get(4).getTimeSeriesList().get(0).getPoints().size()).isEqualTo(1);
+    assertThat(metrics.get(4).getTimeSeriesList().get(0).getPoints().get(0).getValue())
+        .isEqualTo(Value.doubleValue(1234.0));
+    assertThat(metrics.get(4).getTimeSeriesList().get(0).getStartTimestamp()).isEqualTo(null);
+
+    assertThat(metrics.get(5).getMetricDescriptor())
+        .isEqualTo(
+            MetricDescriptor.create(
+                "codahale_long_gauge_gauge",
+                "Collected from codahale (metric=long_gauge, "
+                    + "type=io.opencensus.contrib.dropwizard.DropWizardMetricsTest$3)",
+                DEFAULT_UNIT,
+                Type.GAUGE_DOUBLE,
+                Collections.<LabelKey>emptyList()));
+    assertThat(metrics.get(5).getTimeSeriesList().size()).isEqualTo(1);
+    assertThat(metrics.get(5).getTimeSeriesList().get(0).getLabelValues().size()).isEqualTo(0);
+    assertThat(metrics.get(5).getTimeSeriesList().get(0).getPoints().size()).isEqualTo(1);
+    assertThat(metrics.get(5).getTimeSeriesList().get(0).getPoints().get(0).getValue())
+        .isEqualTo(Value.doubleValue(1234.0));
+    assertThat(metrics.get(5).getTimeSeriesList().get(0).getStartTimestamp()).isEqualTo(null);
+
+    assertThat(metrics.get(6).getMetricDescriptor())
+        .isEqualTo(
+            MetricDescriptor.create(
+                "codahale_get_requests_meter",
+                "Collected from codahale (metric=get_requests, "
+                    + "type=com.codahale.metrics.Meter)",
+                DEFAULT_UNIT,
+                Type.CUMULATIVE_INT64,
+                Collections.<LabelKey>emptyList()));
+    assertThat(metrics.get(6).getTimeSeriesList().size()).isEqualTo(1);
+    assertThat(metrics.get(6).getTimeSeriesList().get(0).getLabelValues().size()).isEqualTo(0);
+    assertThat(metrics.get(6).getTimeSeriesList().get(0).getPoints().size()).isEqualTo(1);
+    assertThat(metrics.get(6).getTimeSeriesList().get(0).getPoints().get(0).getValue())
+        .isEqualTo(Value.longValue(2));
+    assertThat(metrics.get(6).getTimeSeriesList().get(0).getStartTimestamp()).isEqualTo(null);
+
+    assertThat(metrics.get(7).getMetricDescriptor())
+        .isEqualTo(
+            MetricDescriptor.create(
+                "codahale_get_requests_meter_rate",
+                "Collected from codahale (metric=get_requests, "
+                    + "type=com.codahale.metrics.Meter)",
+                "events/second",
+                Type.GAUGE_DOUBLE,
+                RATE_LABEL_KEY));
+    assertThat(metrics.get(7).getTimeSeriesList().size()).isEqualTo(4);
+    assertThat(metrics.get(7).getTimeSeriesList().get(0).getLabelValues().size()).isEqualTo(1);
+    assertThat(metrics.get(7).getTimeSeriesList().get(0).getLabelValues())
+        .isEqualTo(RATE_MEAN_LABEL_VALUE);
+    assertThat(metrics.get(7).getTimeSeriesList().get(0).getPoints().size()).isEqualTo(1);
+    assertThat(metrics.get(7).getTimeSeriesList().get(0).getPoints()).isNotEmpty();
+    assertThat(metrics.get(7).getTimeSeriesList().get(0).getStartTimestamp()).isEqualTo(null);
+
+    assertThat(metrics.get(7).getTimeSeriesList().get(1).getLabelValues())
+        .isEqualTo(RATE_ONE_MINUTE_LABEL_VALUE);
+    assertThat(metrics.get(7).getTimeSeriesList().get(1).getPoints().size()).isEqualTo(1);
+    assertThat(metrics.get(7).getTimeSeriesList().get(1).getPoints()).isNotEmpty();
+    assertThat(metrics.get(7).getTimeSeriesList().get(1).getStartTimestamp()).isEqualTo(null);
+
+    assertThat(metrics.get(7).getTimeSeriesList().get(2).getLabelValues())
+        .isEqualTo(RATE_FIVE_MINUTE_LABEL_VALUE);
+    assertThat(metrics.get(7).getTimeSeriesList().get(2).getPoints().size()).isEqualTo(1);
+    assertThat(metrics.get(7).getTimeSeriesList().get(2).getPoints()).isNotEmpty();
+    assertThat(metrics.get(7).getTimeSeriesList().get(2).getStartTimestamp()).isEqualTo(null);
+
+    assertThat(metrics.get(7).getTimeSeriesList().get(3).getLabelValues())
+        .isEqualTo(RATE_FIFTEEN_MINUTE_LABEL_VALUE);
+    assertThat(metrics.get(7).getTimeSeriesList().get(3).getPoints().size()).isEqualTo(1);
+    assertThat(metrics.get(7).getTimeSeriesList().get(3).getPoints()).isNotEmpty();
+    assertThat(metrics.get(7).getTimeSeriesList().get(3).getStartTimestamp()).isEqualTo(null);
+
+    assertThat(metrics.get(8).getMetricDescriptor())
+        .isEqualTo(
+            MetricDescriptor.create(
+                "codahale_result_histogram",
+                "Collected from codahale (metric=result, " + "type=com.codahale.metrics.Histogram)",
+                DEFAULT_UNIT,
+                Type.SUMMARY,
+                Collections.<LabelKey>emptyList()));
+    assertThat(metrics.get(8).getTimeSeriesList().size()).isEqualTo(1);
+    assertThat(metrics.get(8).getTimeSeriesList().get(0).getLabelValues().size()).isEqualTo(0);
+    assertThat(metrics.get(8).getTimeSeriesList().get(0).getPoints().size()).isEqualTo(1);
+    assertThat(metrics.get(8).getTimeSeriesList().get(0).getPoints().get(0).getValue())
+        .isEqualTo(
+            Value.summaryValue(
+                Summary.create(
+                    1L,
+                    0.0,
+                    Snapshot.create(
+                        1L,
+                        0.0,
+                        Arrays.asList(
+                            ValueAtPercentile.create(50.0, 200.0),
+                            ValueAtPercentile.create(75.0, 200.0),
+                            ValueAtPercentile.create(98.0, 200.0),
+                            ValueAtPercentile.create(99.0, 200.0),
+                            ValueAtPercentile.create(99.9, 200.0))))));
+    assertThat(metrics.get(8).getTimeSeriesList().get(0).getStartTimestamp())
+        .isInstanceOf(Timestamp.class);
+
+    assertThat(metrics.get(9).getMetricDescriptor())
+        .isEqualTo(
+            MetricDescriptor.create(
+                "codahale_requests_timer",
+                "Collected from codahale (metric=requests, " + "type=com.codahale.metrics.Timer)",
+                DEFAULT_UNIT,
+                Type.SUMMARY,
+                Collections.<LabelKey>emptyList()));
+    assertThat(metrics.get(9).getTimeSeriesList().size()).isEqualTo(1);
+    assertThat(metrics.get(9).getTimeSeriesList().get(0).getLabelValues().size()).isEqualTo(0);
+    assertThat(metrics.get(9).getTimeSeriesList().get(0).getPoints().size()).isEqualTo(1);
+    assertThat(metrics.get(9).getTimeSeriesList().get(0).getPoints().get(0).getValue())
+        .isEqualTo(
+            Value.summaryValue(
+                Summary.create(
+                    1L,
+                    0.0,
+                    Snapshot.create(
+                        1L,
+                        0.0,
+                        Arrays.asList(
+                            ValueAtPercentile.create(50.0, timer.getSnapshot().getMedian()),
+                            ValueAtPercentile.create(75.0, timer.getSnapshot().get75thPercentile()),
+                            ValueAtPercentile.create(98.0, timer.getSnapshot().get98thPercentile()),
+                            ValueAtPercentile.create(99.0, timer.getSnapshot().get99thPercentile()),
+                            ValueAtPercentile.create(
+                                99.9, timer.getSnapshot().get999thPercentile()))))));
+
+    assertThat(metrics.get(9).getTimeSeriesList().get(0).getStartTimestamp())
+        .isInstanceOf(Timestamp.class);
+  }
+
+  @Test
+  public void empty_GetMetrics() {
+    assertThat(dropWizardMetrics.getMetrics()).isEmpty();
+  }
+}
diff --git a/contrib/dropwizard/src/test/java/io/opencensus/contrib/dropwizard/DropWizardUtilsTest.java b/contrib/dropwizard/src/test/java/io/opencensus/contrib/dropwizard/DropWizardUtilsTest.java
new file mode 100644
index 00000000..4dd27f29
--- /dev/null
+++ b/contrib/dropwizard/src/test/java/io/opencensus/contrib/dropwizard/DropWizardUtilsTest.java
@@ -0,0 +1,41 @@
+/*
+ * Copyright 2018, OpenCensus 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
+ *
+ *     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 io.opencensus.contrib.dropwizard;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.codahale.metrics.Counter;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Tests for {@link DropWizardUtils}. */
+@RunWith(JUnit4.class)
+public class DropWizardUtilsTest {
+
+  @Test
+  public void generateFullMetricName() {
+    assertThat(DropWizardUtils.generateFullMetricName("requests", "gauge"))
+        .isEqualTo("codahale_requests_gauge");
+  }
+
+  @Test
+  public void generateFullMetricDescription() {
+    assertThat(DropWizardUtils.generateFullMetricDescription("Counter", new Counter()))
+        .isEqualTo("Collected from codahale (metric=Counter, type=com.codahale.metrics.Counter)");
+  }
+}
diff --git a/settings.gradle b/settings.gradle
index bdf68bdc..7c224edf 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -16,6 +16,7 @@ include ":opencensus-exporter-stats-stackdriver"
 include ":opencensus-exporter-stats-prometheus"
 include ":opencensus-contrib-agent"
 include ":opencensus-contrib-appengine-standard-util"
+include ":opencensus-contrib-dropwizard"
 include ":opencensus-contrib-exemplar-util"
 include ":opencensus-contrib-grpc-metrics"
 include ":opencensus-contrib-grpc-util"
@@ -34,6 +35,7 @@ project(':opencensus-testing').projectDir = "$rootDir/testing" as File
 project(':opencensus-contrib-agent').projectDir = "$rootDir/contrib/agent" as File
 project(':opencensus-contrib-appengine-standard-util').projectDir =
         "$rootDir/contrib/appengine_standard_util" as File
+project(':opencensus-contrib-dropwizard').projectDir = "$rootDir/contrib/dropwizard" as File
 project(':opencensus-contrib-exemplar-util').projectDir = "$rootDir/contrib/exemplar_util" as File
 project(':opencensus-contrib-grpc-metrics').projectDir = "$rootDir/contrib/grpc_metrics" as File
 project(':opencensus-contrib-grpc-util').projectDir = "$rootDir/contrib/grpc_util" as File