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# 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
### 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