First you need to define a Listener to your web.xml:
<listener>
<listener-class>com.company.urltesting.MetricsListener</listener-class>
</listener>
The logic in the Listener is pretty straightforward:
import com.codahale.metrics.MetricRegistry;
import com.codahale.metrics.servlets.MetricsServlet;
public class MetricsListener extends MetricsServlet.ContextListener {
public static final MetricRegistry REGISTRY = new MetricRegistry();
@Override
protected MetricRegistry getMetricRegistry() {
return REGISTRY;
}
}
The 'magic' here is the Coda Hale logic will call your listener to setup the Registry the first time. It isn't clear here but it is adding a specifically named Registry to the SessionContext (more about this in a minute).
Next setup the Servlet filter to be able to query the Metrics via an HTTP browser:
<servlet>
<servlet-name>CodahaleMetrics</servlet-name>
<servlet-class>com.codahale.metrics.servlets.MetricsServlet</servlet-class>
<init-param>
<param-name>metrics-uri</param-name>
<param-value>/metrics</param-value>
</init-param>
<init-param>
<param-name>ping-uri</param-name>
<param-value>/ping</param-value>
</init-param>
<init-param>
<param-name>healthcheck-uri</param-name>
<param-value>/health</param-value>
</init-param>
<init-param>
<param-name>threads-uri</param-name>
<param-value>/threads</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>CodahaleMetrics</servlet-name>
<url-pattern>/CodahaleMetrics/*</url-pattern>
</servlet-mapping>
Finally, to create/use a Metric you need to know how to get them yourself from the Session Context.
Here is the most basic use:
import com.codahale.metrics.MetricRegistry;
import com.codahale.metrics.Timer;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Encrypted extends HttpServlet {
// public static final MetricRegistry metrics = new MetricRegistry();
public void service(HttpServletRequest request,
HttpServletResponse response) {
ServletContext servletContext = getServletContext();
MetricRegistry metrics = (MetricRegistry) servletContext.getAttribute("com.codahale.metrics.servlets.MetricsServlet.registry");
Timer tempTimer = metrics.timer(MetricRegistry.name(Encrypted.class, "Encrypted"));
final Timer.Context context = tempTimer.time();
// do your work
context.stop();
}
}
Note the 'magic' string in the getAttribute call on the Servlet Context. The Metrics library adds this during startup if you've provided the Listener we defined in the first step.
Finally, hit the reporting URL to see your Metric values:
http://localhost:8080/CodahaleMetrics/metrics
{"version":"3.0.0","gauges":{},"counters":{},"histograms":{},"meters":{},"timers":{"com.company.urltesting.Encrypted.Encrypted":{"count":1,"max":0.21837355500000002,"mean":0.21837355500000002,"min":0.21837355500000002,
"p50":0.21837355500000002,"p75":0.21837355500000002,"p95":0.21837355500000002,
"p98":0.21837355500000002,"p99":0.21837355500000002,"p999":0.21837355500000002,
"stddev":0.0,"m15_rate":0.0,"m1_rate":0.0,"m5_rate":0.0,"mean_rate":0.2579625731812282,
"duration_units":"seconds","rate_units":"calls/second"}}}
