Einführung in Dropwizard-Metriken

1. Einleitung

Metrics ist eine Java-Bibliothek, die Messinstrumente für Java-Anwendungen bereitstellt.

Es besteht aus mehreren Modulen. In diesem Artikel werden wir das Metrik-Core-Modul, das Metrik-Healthchecks-Modul, das Metrik-Servlet-Modul und das Metrik-Servlet-Modul erläutern und den Rest als Referenz skizzieren.

2. Modul Metrics-Core

2.1. Maven-Abhängigkeiten

Für die Verwendung des Metrics-Core- Moduls ist nur eine Abhängigkeit erforderlich, die der Datei pom.xml hinzugefügt werden muss:

 io.dropwizard.metrics metrics-core 3.1.2  

Die neueste Version finden Sie hier.

2.2. MetricRegistry

Einfach ausgedrückt, verwenden wir die MetricRegistry- Klasse, um eine oder mehrere Metriken zu registrieren.

Wir können eine Metrikregistrierung für alle unsere Metriken verwenden. Wenn wir jedoch unterschiedliche Berichtsmethoden für unterschiedliche Metriken verwenden möchten, können wir unsere Metriken auch in Gruppen unterteilen und für jede Gruppe unterschiedliche Metrikregister verwenden.

Erstellen wir jetzt eine MetricRegistry :

MetricRegistry metricRegistry = new MetricRegistry();

Und dann können wir einige Metriken bei dieser MetricRegistry registrieren :

Meter meter1 = new Meter(); metricRegistry.register("meter1", meter1); Meter meter2 = metricRegistry.meter("meter2"); 

Es gibt zwei grundlegende Möglichkeiten, eine neue Metrik zu erstellen: eine selbst zu instanziieren oder eine aus der Metrikregistrierung zu erhalten. Wie Sie sehen können, haben wir beide im obigen Beispiel verwendet. Wir instanziieren das Meter- Objekt "meter1" und erhalten ein weiteres Meter- Objekt "meter2", das von der metricRegistry erstellt wird .

In einer Metrikregistrierung hat jede Metrik einen eindeutigen Namen, da wir oben "meter1" und "meter2" als Metriknamen verwendet haben. MetricRegistry bietet auch eine Reihe statischer Hilfsmethoden , mit denen wir die richtigen Metriknamen erstellen können:

String name1 = MetricRegistry.name(Filter.class, "request", "count"); String name2 = MetricRegistry.name("CustomFilter", "response", "count"); 

Wenn wir eine Reihe von Metrikregistern verwalten müssen, können wir die SharedMetricRegistries- Klasse verwenden, die singleton- und threadsicher ist. Wir können ein Metrikregister hinzufügen, dieses Metrikregister daraus abrufen und es entfernen:

SharedMetricRegistries.add("default", metricRegistry); MetricRegistry retrievedMetricRegistry = SharedMetricRegistries.getOrCreate("default"); SharedMetricRegistries.remove("default"); 

3. Metrikkonzepte

Das Metrik-Kern-Modul bietet mehrere häufig verwendete Metriktypen: Messgerät , Messgerät , Zähler , Histogramm und Timer sowie Reporter zur Ausgabe der Metrikwerte .

3.1. Meter

Ein Messgerät misst die Anzahl und Rate der Ereignisse:

Meter meter = new Meter(); long initCount = meter.getCount(); assertThat(initCount, equalTo(0L)); meter.mark(); assertThat(meter.getCount(), equalTo(1L)); meter.mark(20); assertThat(meter.getCount(), equalTo(21L)); double meanRate = meter.getMeanRate(); double oneMinRate = meter.getOneMinuteRate(); double fiveMinRate = meter.getFiveMinuteRate(); double fifteenMinRate = meter.getFifteenMinuteRate(); 

Die Methode getCount () gibt die Anzahl der Ereignisereignisse zurück, und die Methode mark () addiert 1 oder n zur Anzahl der Ereignisereignisse. Das Messgerät- Objekt bietet vier Raten, die Durchschnittsraten für die gesamte Lebensdauer des Messgeräts für die letzte Minute, für die letzten fünf Minuten bzw. für das letzte Quartal darstellen.

3.2. Spur

Gauge ist eine Schnittstelle, über die einfach ein bestimmter Wert zurückgegeben wird. Das Metrics-Core-Modul bietet verschiedene Implementierungen: RatioGauge , CachedGauge , DerivativeGauge und JmxAttributeGauge .

RatioGauge ist eine abstrakte Klasse und misst das Verhältnis eines Werts zu einem anderen.

Mal sehen, wie man es benutzt. Zuerst implementieren wir eine Klasse AttendanceRatioGauge :

public class AttendanceRatioGauge extends RatioGauge { private int attendanceCount; private int courseCount; @Override protected Ratio getRatio() { return Ratio.of(attendanceCount, courseCount); } // standard constructors } 

Und dann testen wir es:

RatioGauge ratioGauge = new AttendanceRatioGauge(15, 20); assertThat(ratioGauge.getValue(), equalTo(0.75)); 

CachedGauge ist eine weitere abstrakte Klasse, die Werte zwischenspeichern kann. Daher ist es sehr nützlich, wenn die Berechnung der Werte teuer ist. Um es zu verwenden, müssen wir eine Klasse ActiveUsersGauge implementieren :

public class ActiveUsersGauge extends CachedGauge
    
      { @Override protected List loadValue() { return getActiveUserCount(); } private List getActiveUserCount() { List result = new ArrayList(); result.add(12L); return result; } // standard constructors }
    

Dann testen wir es, um zu sehen, ob es wie erwartet funktioniert:

Gauge
    
      activeUsersGauge = new ActiveUsersGauge(15, TimeUnit.MINUTES); List expected = new ArrayList(); expected.add(12L); assertThat(activeUsersGauge.getValue(), equalTo(expected)); 
    

Wir setzen die Ablaufzeit des Caches auf 15 Minuten, wenn wir ActiveUsersGauge instanziieren .

DerivativeGauge ist auch eine abstrakte Klasse und ermöglicht es Ihnen, einen Wert von einem anderen Gauge als dessen Wert abzuleiten .

Schauen wir uns ein Beispiel an:

public class ActiveUserCountGauge extends DerivativeGauge
    
      { @Override protected Integer transform(List value) { return value.size(); } // standard constructors }
    

This Gauge derives its value from an ActiveUsersGauge, so we expect it to be the value from the base list's size:

Gauge
    
      activeUsersGauge = new ActiveUsersGauge(15, TimeUnit.MINUTES); Gauge activeUserCountGauge = new ActiveUserCountGauge(activeUsersGauge); assertThat(activeUserCountGauge.getValue(), equalTo(1)); 
    

JmxAttributeGauge is used when we need to access other libraries' metrics exposed via JMX.

3.3. Counter

The Counter is used for recording incrementations and decrementations:

Counter counter = new Counter(); long initCount = counter.getCount(); assertThat(initCount, equalTo(0L)); counter.inc(); assertThat(counter.getCount(), equalTo(1L)); counter.inc(11); assertThat(counter.getCount(), equalTo(12L)); counter.dec(); assertThat(counter.getCount(), equalTo(11L)); counter.dec(6); assertThat(counter.getCount(), equalTo(5L));

3.4. Histogram

Histogram is used for keeping track of a stream of Long values and it analyzes their statistical characteristics such as max, min, mean, median, standard deviation, 75th percentile and so on:

Histogram histogram = new Histogram(new UniformReservoir()); histogram.update(5); long count1 = histogram.getCount(); assertThat(count1, equalTo(1L)); Snapshot snapshot1 = histogram.getSnapshot(); assertThat(snapshot1.getValues().length, equalTo(1)); assertThat(snapshot1.getValues()[0], equalTo(5L)); histogram.update(20); long count2 = histogram.getCount(); assertThat(count2, equalTo(2L)); Snapshot snapshot2 = histogram.getSnapshot(); assertThat(snapshot2.getValues().length, equalTo(2)); assertThat(snapshot2.getValues()[1], equalTo(20L)); assertThat(snapshot2.getMax(), equalTo(20L)); assertThat(snapshot2.getMean(), equalTo(12.5)); assertEquals(10.6, snapshot2.getStdDev(), 0.1); assertThat(snapshot2.get75thPercentile(), equalTo(20.0)); assertThat(snapshot2.get999thPercentile(), equalTo(20.0)); 

Histogram samples the data by using reservoir sampling, and when we instantiate a Histogram object, we need to set its reservoir explicitly.

Reservoir is an interface and metrics-core provides four implementations of them: ExponentiallyDecayingReservoir, UniformReservoir, SlidingTimeWindowReservoir, SlidingWindowReservoir.

In the section above, we mentioned that a metric can also be created by MetricRegistry, besides using a constructor. When we use metricRegistry.histogram(), it returns a Histogram instance with ExponentiallyDecayingReservoir implementation.

3.5. Timer

Timer is used for keeping track of multiple timing durations which are represented by Context objects, and it also provides their statistical data:

Timer timer = new Timer(); Timer.Context context1 = timer.time(); TimeUnit.SECONDS.sleep(5); long elapsed1 = context1.stop(); assertEquals(5000000000L, elapsed1, 1000000); assertThat(timer.getCount(), equalTo(1L)); assertEquals(0.2, timer.getMeanRate(), 0.1); Timer.Context context2 = timer.time(); TimeUnit.SECONDS.sleep(2); context2.close(); assertThat(timer.getCount(), equalTo(2L)); assertEquals(0.3, timer.getMeanRate(), 0.1); 

3.6. Reporter

When we need to output our measurements, we can use Reporter. This is an interface, and the metrics-core module provides several implementations of it, such as ConsoleReporter, CsvReporter, Slf4jReporter, JmxReporter and so on.

Here we use ConsoleReporter as an example:

MetricRegistry metricRegistry = new MetricRegistry(); Meter meter = metricRegistry.meter("meter"); meter.mark(); meter.mark(200); Histogram histogram = metricRegistry.histogram("histogram"); histogram.update(12); histogram.update(17); Counter counter = metricRegistry.counter("counter"); counter.inc(); counter.dec(); ConsoleReporter reporter = ConsoleReporter.forRegistry(metricRegistry).build(); reporter.start(5, TimeUnit.MICROSECONDS); reporter.report(); 

Here is the sample output of the ConsoleReporter:

-- Histograms ------------------------------------------------------------------ histogram count = 2 min = 12 max = 17 mean = 14.50 stddev = 2.50 median = 17.00 75% <= 17.00 95% <= 17.00 98% <= 17.00 99% <= 17.00 99.9% <= 17.00 -- Meters ---------------------------------------------------------------------- meter count = 201 mean rate = 1756.87 events/second 1-minute rate = 0.00 events/second 5-minute rate = 0.00 events/second 15-minute rate = 0.00 events/second 

4. Module metrics-healthchecks

Metrics has an extension metrics-healthchecks module for dealing with health checks.

4.1. Maven Dependencies

To use the metrics-healthchecks module, we need to add this dependency to the pom.xml file:

 io.dropwizard.metrics metrics-healthchecks 3.1.2 

And you can find its latest version here.

4.2. Usage

First, we need several classes which are responsible for specific health check operations, and these classes must implement HealthCheck.

For example, we use DatabaseHealthCheck and UserCenterHealthCheck:

public class DatabaseHealthCheck extends HealthCheck { @Override protected Result check() throws Exception { return Result.healthy(); } } 
public class UserCenterHealthCheck extends HealthCheck { @Override protected Result check() throws Exception { return Result.healthy(); } } 

Then, we need a HealthCheckRegistry (which is just like MetricRegistry), and register the DatabaseHealthCheck and UserCenterHealthCheck with it:

HealthCheckRegistry healthCheckRegistry = new HealthCheckRegistry(); healthCheckRegistry.register("db", new DatabaseHealthCheck()); healthCheckRegistry.register("uc", new UserCenterHealthCheck()); assertThat(healthCheckRegistry.getNames().size(), equalTo(2)); 

We can also unregister the HealthCheck:

healthCheckRegistry.unregister("uc"); assertThat(healthCheckRegistry.getNames().size(), equalTo(1)); 

We can run all the HealthCheck instances:

Map results = healthCheckRegistry.runHealthChecks(); for (Map.Entry entry : results.entrySet()) { assertThat(entry.getValue().isHealthy(), equalTo(true)); } 

Finally, we can run a specific HealthCheck instance:

healthCheckRegistry.runHealthCheck("db"); 

5. Module metrics-servlets

Metrics provides us a handful of useful servlets which allow us to access metrics related data through HTTP requests.

5.1. Maven Dependencies

To use the metrics-servlets module, we need to add this dependency to the pom.xml file:

 io.dropwizard.metrics metrics-servlets 3.1.2 

And you can find its latest version here.

5.2. HealthCheckServlet Usage

HealthCheckServlet provides health check results. First, we need to create a ServletContextListener which exposes our HealthCheckRegistry:

public class MyHealthCheckServletContextListener extends HealthCheckServlet.ContextListener { public static HealthCheckRegistry HEALTH_CHECK_REGISTRY = new HealthCheckRegistry(); static { HEALTH_CHECK_REGISTRY.register("db", new DatabaseHealthCheck()); } @Override protected HealthCheckRegistry getHealthCheckRegistry() { return HEALTH_CHECK_REGISTRY; } } 

Then, we add both this listener and HealthCheckServlet into the web.xml file:

 com.baeldung.metrics.servlets.MyHealthCheckServletContextListener   healthCheck com.codahale.metrics.servlets.HealthCheckServlet   healthCheck /healthcheck 

Now we can start the web application, and send a GET request to “//localhost:8080/healthcheck” to get health check results. Its response should be like this:

{ "db": { "healthy": true } }

5.3. ThreadDumpServlet Usage

ThreadDumpServlet provides information about all live threads in the JVM, their states, their stack traces, and the state of any locks they may be waiting for.

If we want to use it, we simply need to add these into the web.xml file:

 threadDump com.codahale.metrics.servlets.ThreadDumpServlet   threadDump /threaddump 

Thread dump data will be available at “//localhost:8080/threaddump”.

5.4. PingServlet Usage

PingServlet can be used to test if the application is running. We add these into the web.xml file:

 ping com.codahale.metrics.servlets.PingServlet   ping /ping 

And then send a GET request to “//localhost:8080/ping”. The response's status code is 200 and its content is “pong”.

5.5. MetricsServlet Usage

MetricsServlet provides metrics data. First, we need to create a ServletContextListener which exposes our MetricRegistry:

public class MyMetricsServletContextListener extends MetricsServlet.ContextListener { private static MetricRegistry METRIC_REGISTRY = new MetricRegistry(); static { Counter counter = METRIC_REGISTRY.counter("m01-counter"); counter.inc(); Histogram histogram = METRIC_REGISTRY.histogram("m02-histogram"); histogram.update(5); histogram.update(20); histogram.update(100); } @Override protected MetricRegistry getMetricRegistry() { return METRIC_REGISTRY; } } 

Both this listener and MetricsServlet need to be added into web.xml:

 com.codahale.metrics.servlets.MyMetricsServletContextListener   metrics com.codahale.metrics.servlets.MetricsServlet   metrics /metrics 

This will be exposed in our web application at “//localhost:8080/metrics”. Its response should contain various metrics data:

{ "version": "3.0.0", "gauges": {}, "counters": { "m01-counter": { "count": 1 } }, "histograms": { "m02-histogram": { "count": 3, "max": 100, "mean": 41.66666666666666, "min": 5, "p50": 20, "p75": 100, "p95": 100, "p98": 100, "p99": 100, "p999": 100, "stddev": 41.69998667732268 } }, "meters": {}, "timers": {} } 

5.6. AdminServlet Usage

AdminServlet aggregates HealthCheckServlet, ThreadDumpServlet, MetricsServlet, and PingServlet.

Let's add these into the web.xml:

 admin com.codahale.metrics.servlets.AdminServlet   admin /admin/* 

It can now be accessed at “//localhost:8080/admin”. We will get a page containing four links, one for each of those four servlets.

Note that, if we want to do health check and access metrics data, those two listeners are still needed.

6. Module metrics-servlet

The metrics-servlet module provides a Filter which has several metrics: meters for status codes, a counter for the number of active requests, and a timer for request duration.

6.1. Maven Dependencies

To use this module, let's first add the dependency into the pom.xml:

 io.dropwizard.metrics metrics-servlet 3.1.2 

And you can find its latest version here.

6.2. Usage

To use it, we need to create a ServletContextListener which exposes our MetricRegistry to the InstrumentedFilter:

public class MyInstrumentedFilterContextListener extends InstrumentedFilterContextListener { public static MetricRegistry REGISTRY = new MetricRegistry(); @Override protected MetricRegistry getMetricRegistry() { return REGISTRY; } } 

Then, we add these into the web.xml:

  com.baeldung.metrics.servlet.MyInstrumentedFilterContextListener    instrumentFilter  com.codahale.metrics.servlet.InstrumentedFilter    instrumentFilter /* 

Now the InstrumentedFilter can work. If we want to access its metrics data, we can do it through its MetricRegistryREGISTRY.

7. Other Modules

Except for the modules we introduced above, Metrics has some other modules for different purposes:

  • metrics-jvm: provides several useful metrics for instrumenting JVM internals
  • metrics-ehcache: provides InstrumentedEhcache, a decorator for Ehcache caches
  • metrics-httpclient: provides classes for instrumenting Apache HttpClient (4.x version)
  • metrics-log4j: provides InstrumentedAppender, a Log4j Appender implementation for log4j 1.x which records the rate of logged events by their logging level
  • metrics-log4j2: is similar to metrics-log4j, just for log4j 2.x
  • metrics-logback: provides InstrumentedAppender, a Logback Appender implementation which records the rate of logged events by their logging level
  • metrics-json : bietet HealthCheckModule und MetricsModule für Jackson

Abgesehen von diesen Hauptprojektmodulen bieten einige andere Bibliotheken von Drittanbietern die Integration mit anderen Bibliotheken und Frameworks.

8. Fazit

Das Instrumentieren von Anwendungen ist eine häufige Anforderung. In diesem Artikel haben wir Metriken vorgestellt, in der Hoffnung, dass sie Ihnen bei der Lösung Ihres Problems helfen können.

Wie immer ist der vollständige Quellcode für das Beispiel auf GitHub verfügbar.