Measure with Wicket metrics

Use this when you want numbers on what your Wicket application does: how many requests it serves, how long components take to construct and render, how often models load. The module wicket-metrics weaves measuring code into Wicket’s classes with AspectJ and collects the results in a Dropwizard Metrics registry.

wicket-metrics is experimental: it lives in the wicket-experimental part of the Wicket build and may change or disappear in a later release. It is published with every Wicket release, with the same version number.

Add the dependencies

<dependency>
    <groupId>org.apache.wicket.experimental.wicket10</groupId>
    <artifactId>wicket-metrics</artifactId>
    <version>${wicket.version}</version>
</dependency>
<dependency>
    <groupId>org.aspectj</groupId>
    <artifactId>aspectjrt</artifactId>
    <version>${aspectj.version}</version>
</dependency>

wicket-metrics brings Dropwizard’s metrics-core and metrics-jmx along. AspectJ is licensed under the Eclipse Public License; include its license when you distribute it.

Start the AspectJ weaver

The measurements are added while classes load, by the AspectJ weaver running as a Java agent. Download aspectjweaver.jar in the same version as aspectjrt and add it to the JVM options of your servlet container, for example in Tomcat’s setenv.sh:

CATALINA_OPTS="$CATALINA_OPTS -javaagent:/opt/aspectj/aspectjweaver-1.9.x.jar"

Choose the measurements

Create src/main/resources/META-INF/aop.xml. It tells the weaver which Wicket classes to weave and which aspects to apply. WicketFilterInitAspect is required; the others are optional:

<!DOCTYPE aspectj PUBLIC "-//AspectJ//DTD//EN" "http://www.eclipse.org/aspectj/dtd/aspectj.dtd">
<aspectj>
    <weaver options="-nowarn">
        <include within="org.apache.wicket..*"/>
    </weaver>
    <aspects>
        <aspect name="org.apache.wicket.metrics.aspects.WicketFilterInitAspect"/>
        <aspect name="org.apache.wicket.metrics.aspects.request.WicketFilterRequestCycleAspect"/>
        <aspect name="org.apache.wicket.metrics.aspects.component.ComponentCreateAspect"/>
        <aspect name="org.apache.wicket.metrics.aspects.component.ComponentOnRenderAspect"/>
        <aspect name="org.apache.wicket.metrics.aspects.model.LoadableDetachableModelLoadAspect"/>
    </aspects>
</aspectj>

The jar contains wicket-metrics.template.xml with every aspect. The aspects are in subpackages of org.apache.wicket.metrics.aspects:

Each metric name starts with the name of the Wicket filter and, where it measures a class, ends with that class name.

The session count also needs the servlet listener org.apache.wicket.metrics.aspects.session.SessionCountListener. It is annotated with @WebListener, so the container finds it, unless your web.xml is metadata-complete="true"; then declare it in web.xml. The count starts at 0 when the server starts, so clear persisted sessions when you restart, or the number is off.

wicket-metrics supports one Wicket filter per web application.

Read the measurements in JMX

Publish the registry as JMX MBeans in your application’s init(), then open them in JConsole or VisualVM:

@Override
protected void init() {
    super.init();
    WicketMetrics.getSettings().startJmxReporter();
}

Timers show count, minimum, maximum, mean and percentiles; meters show counts and rates.

Send the measurements elsewhere

WicketMetrics.getMetricRegistry() returns the Dropwizard MetricRegistry, so every Dropwizard reporter works. To send the numbers to Graphite every five seconds, add io.dropwizard.metrics:metrics-graphite in the version that wicket-metrics uses, and start a reporter:

private GraphiteReporter reporter;

@Override
protected void init() {
    super.init();
    var graphite = new Graphite(new InetSocketAddress("graphite.example.com", 2003));
    reporter = GraphiteReporter.forRegistry(WicketMetrics.getMetricRegistry())
        .prefixedWith("webapps")
        .convertRatesTo(TimeUnit.SECONDS)
        .convertDurationsTo(TimeUnit.MILLISECONDS)
        .build(graphite);
    reporter.start(5, TimeUnit.SECONDS);
}

@Override
protected void onDestroy() {
    reporter.stop();
    super.onDestroy();
}

Turn measuring off

WicketMetrics.getSettings().setEnabled(false);

The woven code stays in place but stops recording. To remove it entirely, start the JVM without the weaver agent.

Measure your own code

An aspect that extends WicketMetrics can use its measureTime(), mark() and count() methods:

@Aspect
public class CheckoutAspect extends WicketMetrics {

    @Around("execution(* com.example.shop.CheckoutPage.onSubmit(..))")
    public Object aroundSubmit(ProceedingJoinPoint joinPoint) throws Throwable {
        return measureTime("shop/checkout/submit", joinPoint);
    }
}

Add the aspect to aop.xml, and add your package to the weaver: <include within="com.example.shop..*"/>.