CDI Extension for Metrics

CDI portable extension for Dropwizard Metrics compliant with JSR 346: Contexts and Dependency Injection for Java^TM EE 1.2.

About

Metrics CDI provides support for the Metrics annotations in CDI enabled environments. It implements the contract specified by these annotations with the following level of functionality:

• Intercepts invocations of bean constructors, methods and public methods of bean classes annotated with @Counted, @ExceptionMetered, @Metered and @Timed,
• Creates Gauge and CachedGauge instances for bean methods annotated with @Gauge and @CachedGauge respectively,
• Injects Counter, Gauge, Histogram, Meter and Timer instances,
• Registers or retrieves the produced Metric instances in the resolved MetricRegistry bean,
• Declares automatically a default MetricRegistry bean if no one exists in the CDI container,
• Registers HealthCheck beans with a provided or automatically configured HealthCheckRegistry bean instance.

Metrics CDI is compatible with Metrics version 3.1.0+.

Getting Started

Using Maven

Add the metrics-cdi library as a dependency:

<dependency>
    <groupId>io.astefanutti.metrics.cdi</groupId>
    <artifactId>metrics-cdi</artifactId>
    <version>1.6.0</version>
</dependency>

Required Dependencies

Besides depending on Metrics (metrics-core and metrics-annotation modules), Metrics CDI requires a CDI enabled environment running in Java 8 or greater.

Supported Containers

Metrics CDI is currently successfully tested with the following containers:

Container	Version	Environment
Weld	2.4.3.Final	Java SE 8 / CDI 1.2
Weld	3.0.3.Final	Java SE 8 / CDI 2.0
OpenWebBeans	1.7.3	Java SE 8 / CDI 1.2
Jetty	9.4.5	Servlet 3.1
WildFly 10	10.1.0.Final	Java EE 7

Usage

Metrics CDI activates the Metrics AOP Instrumentation for beans annotated with Metrics annotations and automatically registers the corresponding Metric instances in the Metrics registry resolved for the CDI application. The registration of these Metric instances happens each time such a bean gets instantiated. Besides, Metric instances can be retrieved from the Metrics registry by declaring metrics injection points.

The metrics registration mechanism can be used to customize the Metric instances that get registered. Besides, the Metrics registry resolution mechanism can be used for the application to provide a custom MetricRegistry instance.

Health checks support is automatically activated when the metrics-healthchecks optional dependency is present in the classpath.

Metrics AOP Instrumentation

Metrics comes with the metrics-annotation module that contains a set of annotations and provides a standard way to integrate Metrics with frameworks supporting Aspect Oriented Programming (AOP). These annotations are supported by Metrics CDI that implements their contract as documented in their Javadoc.

For example, a method of a bean can be annotated so that its execution can be monitored using Metrics:

import com.codahale.metrics.annotation.Timed;

class TimedMethodBean {

    @Timed
    void timedMethod() {
        // Timer name => TimedMethodBean.timedMethod
    }
}

or the bean class can be annotated directly so that all its public methods get monitored:

import com.codahale.metrics.annotation.Metered;

@Metered
public class MeteredClassBean {

    public void meteredMethod() {
        // Meter name => MeteredClassBean.meteredMethod
    }
}

or the bean constructor can be annotated so that its instantiations get monitored:

import com.codahale.metrics.annotation.Counted;

class CountedConstructorBean {

    @Counted
    CountedConstructorBean() {
        // Counter name => CountedConstructorBean.CountedConstructorBean
    }
}

The name and absolute attributes available on every Metrics annotation can be used to customize the name of the Metric instance that gets registered in the Metrics registry. The default naming convention being the annotated member simple name relative to the declaring class fully qualified name as illustrated in the above examples.

Metrics Injection

Metric instances can be retrieved from the Metrics registry by declaring an injected field, e.g.:

import com.codahale.metrics.Timer;

import javax.inject.Inject;

class TimerBean {

    @Inject
    private Timer timer; // Timer name => TimerBean.Timer
}

Metric instances can be injected similarly as parameters of any initializer method or bean constructor, e.g.:

import com.codahale.metrics.Timer;

import javax.inject.Inject;

class TimerBean {

    private final Timer timer;

    @Inject
    private TimerBean(Timer timer) { // Timer name => TimerBean.Timer
       this.timer = timer;
    }
}

In the above example, the -parameters compiler option is required to get access to injected parameter name. Indeed, access to parameter names at runtime has been introduced with JEP-118. More information can be found in Obtaining Names of Method Parameters from the Java tutorials. To work around that limitation, or to declare a specific name, the @Metric annotation can be used as documented hereafter.

In order to provide metadata for the Metric instantiation and resolution, the injection point can be annotated with the @Metric annotation, e.g., with an injected field:

import com.codahale.metrics.Timer;
import com.codahale.metrics.annotation.Metric;

import javax.inject.Inject;

@Inject
@Metric(name = "timerName", absolute = true)
private Timer timer; // Timer name => timerName

or when using a bean constructor:

import com.codahale.metrics.Timer;
import com.codahale.metrics.annotation.Metric;

import javax.inject.Inject;

class TimerBean {

    private final Timer timer;

    @Inject
    private TimerBean(@Metric(name = "timerName", absolute = true) Timer timer) {
        // Timer name => timerName
        this.timer = timer;
    }
}

Metrics Registration

While Metrics CDI automatically registers Metric instances during the Metrics AOP instrumentation, it may be necessary for an application to explicitly provide the Metric instances to register. For example, to provide particular Reservoir implementations to histograms or timers, e.g. with a producer field:

import com.codahale.metrics.SlidingTimeWindowReservoir;
import com.codahale.metrics.Timer;
import com.codahale.metrics.annotation.Metric;
import com.codahale.metrics.annotation.Timed;

import javax.enterprise.inject.Produces;

class TimedMethodBean {

    @Produces
    @Metric(name = "customTimer") // Timer name => TimedMethodBean.customTimer
    Timer Timer = new Timer(new SlidingTimeWindowReservoir(1L, TimeUnit.MINUTES));

    @Timed(name = "customTimer")
    void timedMethod() {
        // Timer name => TimedMethodBean.customTimer
    }
}

Another use case is to register custom gauges, e.g. with a producer method:

class CacheHitRatioBean {

    @Inject
    private Meter hits;

    @Timed(name = "calls")
    public void cachedMethod() {
        if (hit) hits.mark();
    }

    @Produces
    @Metric(name = "cache-hits")
    private Gauge<Double> cacheHitRatioGauge(Meter hits, Timer calls) {
        return () -> Ratio.of(hits.getCount(), calls.getCount()).getValue();
    }
}

Metrics Registry Resolution

Metrics CDI automatically registers a MetricRegistry bean into the CDI container to register any Metric instances produced. That default MetricRegistry bean can be injected using standard CDI typesafe resolution, for example, by declaring an injected field:

import com.codahale.metrics.MetricRegistry;

import javax.inject.Inject;

@Inject
private MetricRegistry registry;

or by declaring a bean constructor:

import com.codahale.metrics.MetricRegistry;

import javax.inject.Inject;

class MetricRegistryBean {

    private final MetricRegistry registry;

    @Inject
    private MetricRegistryBean(MetricRegistry registry) {
        this.registry = registry;
    }
}

Otherwise, Metrics CDI uses any MetricRegistry bean declared in the CDI container with the built-in default qualifier @Default so that a custom MetricRegistry can be provided. For example, that custom MetricRegistry can be declared with a producer field:

import com.codahale.metrics.MetricRegistry;

import javax.enterprise.context.ApplicationScoped;
import javax.enterprise.inject.Produces;

@Produces
@ApplicationScoped
private final MetricRegistry registry = new MetricRegistry();

or with a producer method:

import com.codahale.metrics.MetricRegistry;

import javax.enterprise.context.ApplicationScoped;
import javax.enterprise.inject.Produces;

class MetricRegistryFactoryBean {

    @Produces
    @ApplicationScoped
    private MetricRegistry metricRegistry() {
        return new MetricRegistry();
    }
}

Health Checks

Metrics CDI automatically registers a HealthCheckRegistry bean into the CDI container. This follows the same resolution mechanism as that of the Metrics registry, so that the application may provide a custom HealthCheckRegistry instance.

Metrics CDI then automatically registers any HealthCheck instance with the configured HealthCheckRegistry instance. A HealthCheck bean can be declared as any CDI bean, e.g. with a bean class:

import com.codahale.metrics.health.HealthCheck;

import javax.inject.Inject;
import javax.inject.Named;

@Named("databaseHealthCheck")
class DatabaseHealthCheck extends HealthCheck {

    @Inject
    private Database database;

    @Override
    protected Result check() {
        return database.ping()
            ? Result.healthy()
            : Result.unhealthy("Can't ping database!");
    }
}

Metrics CDI Configuration

Metrics CDI fires a MetricsConfiguration event at deployment time that can be used by the application to configure it, e.g.:

import io.astefanutti.metrics.cdi.MetricsConfiguration;

import javax.enterprise.event.Observes;

class MetricsCdiConfiguration {

    static void configure(@Observes MetricsConfiguration metrics) {
        // Use absolute name globally
        metrics.useAbsoluteName(true);
        // Use a uniform reservoir globally
        metrics.reservoirFunction((name, type) -> Optional.of(new UniformReservoir());
    }
}

Note that this event can only be used within the context of the observer method invocation. Any attempt to call one of its methods outside of that context will result in an IllegalStateException to be thrown.

Limitations

CDI 1.2 leverages on Java Interceptors Specification 1.2 to provide the ability to associate interceptors to beans via typesafe interceptor bindings. Interceptors are a mean to separate cross-cutting concerns from the business logic and Metrics CDI is relying on interceptors to implement the support of Metrics annotations in a CDI enabled environment.

CDI 1.2 sets additional restrictions about the type of bean to which an interceptor can be bound. From a Metrics CDI end-user perspective, that implies that the managed beans to be monitored with Metrics (i.e. having at least one member method annotated with one of the Metrics annotations) must be proxyable bean types, as defined in Unproxyable bean types, that are:

• Classes which don’t have a non-private constructor with no parameters,
• Classes which are declared final,
• Classes which have non-static, final methods with public, protected or default visibility,
• Primitive types,
• And array types.

License

Copyright © 2013, Antonin Stefanutti

Published under Apache Software License 2.0, see LICENSE