Load metrics factory service from classpath if available

jaeger-core/README.md

@@ -103,8 +103,10 @@ More information about using the `TracerResolver` can be found [here](../jaeger-
 #### Reporting internal metrics via Micrometer
 
 The Jaeger Java Client collects internal metrics and is able to report them via [Micrometer](http://micrometer.io).
-To accomplish that, include the artifact `io.jaegertracing:jaeger-micrometer` as a dependency to your project and use
-`MicrometerMetricsFactory` like this:
+To accomplish that, include the artifact `io.jaegertracing:jaeger-micrometer` as a dependency to your project. The
+integration should be done automatically via the service loader.
+
+If you prefer a manual configuration, it can be done with a code similar to this:
 
 ```java
 MicrometerMetricsFactory metricsReporter = new MicrometerMetricsFactory();

jaeger-core/src/main/java/io/jaegertracing/Configuration.java

@@ -41,9 +41,11 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.Iterator;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
+import java.util.ServiceLoader;
 import lombok.Getter;
 import lombok.extern.slf4j.Slf4j;
 
@@ -170,6 +172,7 @@ public Configuration(String serviceName) {
     this.serviceName = Tracer.Builder.checkValidServiceName(serviceName);
   }
 
+
   /**
    * @return Configuration object from environmental variables
    */
@@ -192,7 +195,7 @@ public Tracer.Builder getTracerBuilder() {
       codecConfig = new CodecConfiguration();
     }
     if (metricsFactory == null) {
-      metricsFactory = new NoopMetricsFactory();
+      metricsFactory = loadMetricsFactory();
     }
     Metrics metrics = new Metrics(metricsFactory);
     Reporter reporter = reporterConfig.getReporter(metrics);
@@ -223,6 +226,19 @@ public synchronized void closeTracer() {
     }
   }
 
+  private MetricsFactory loadMetricsFactory() {
+    ServiceLoader<MetricsFactory> loader = ServiceLoader.load(MetricsFactory.class);
+
+    Iterator<MetricsFactory> iterator = loader.iterator();
+    if (iterator.hasNext()) {
+      MetricsFactory metricsFactory = iterator.next();
+      log.info("Found a Metrics Factory service: {}", metricsFactory.getClass());
+      return metricsFactory;
+    }
+
+    return new NoopMetricsFactory();
+  }
+
   /**
    * @param metricsFactory the MetricsFactory to use on the Tracer to be built
    */

jaeger-core/src/test/java/io/jaegertracing/ConfigurationTest.java

@@ -26,6 +26,7 @@
 import io.jaegertracing.Configuration.SamplerConfiguration;
 import io.jaegertracing.metrics.InMemoryMetricsFactory;
 import io.jaegertracing.metrics.Metrics;
+import io.jaegertracing.metrics.MockMetricsFactory;
 import io.jaegertracing.propagation.Codec;
 import io.jaegertracing.samplers.ConstSampler;
 import io.jaegertracing.samplers.ProbabilisticSampler;
@@ -432,6 +433,15 @@ private <C> void assertInjectExtract(io.opentracing.Tracer tracer, Format<C> for
     assertEquals(contextToInject.getSpanId(), extractedContext.getSpanId());
   }
 
+  @Test
+  public void testMetricsFactoryFromServiceLoader() {
+    System.setProperty(Configuration.JAEGER_SERVICE_NAME, "Test");
+
+    int instances = MockMetricsFactory.instances.size();
+    Configuration.fromEnv().getTracer();
+    assertEquals(++instances, MockMetricsFactory.instances.size());
+  }
+
   static class TestTextMap implements TextMap {
 
     private Map<String,String> values = new HashMap<>();

jaeger-core/src/test/java/io/jaegertracing/metrics/MockMetricsFactory.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2018, The Jaeger Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+package io.jaegertracing.metrics;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * This metrics factory serves only to get loaded via a service loader, while still keeping compatibility with tests
+ * that make use of the {@link InMemoryMetricsFactory}
+ */
+public class MockMetricsFactory extends InMemoryMetricsFactory {
+  public static final List<MockMetricsFactory> instances = new ArrayList<>();
+
+  public MockMetricsFactory() {
+    instances.add(this);
+  }
+}

jaeger-core/src/test/resources/META-INF/services/io.jaegertracing.metrics.MetricsFactory

@@ -0,0 +1 @@
+io.jaegertracing.metrics.MockMetricsFactory

jaeger-micrometer/src/main/resources/META-INF/services/io.jaegertracing.metrics.MetricsFactory

@@ -0,0 +1 @@
+io.jaegertracing.micrometer.MicrometerMetricsFactory

jaeger-micrometer/src/test/java/io/jaegertracing/micrometer/MicrometerTest.java

@@ -186,6 +186,29 @@ public void validateMetricCounts() throws InterruptedException {
     assertEquals("Wrong number of traces", 10.0, traces, assertDelta);
   }
 
+  @Test
+  public void testServiceLoader() {
+    System.setProperty(Configuration.JAEGER_SAMPLER_TYPE, ConstSampler.TYPE);
+    System.setProperty(Configuration.JAEGER_SAMPLER_PARAM, "1");
+    System.setProperty(Configuration.JAEGER_SERVICE_NAME, "Test");
+
+    // the fact that there's a service on the classpath is enough to get it loaded, unless we have an env var
+    // saying to skip it
+    final Configuration configuration = Configuration.fromEnv();
+
+    System.clearProperty(Configuration.JAEGER_SERVICE_NAME);
+    System.clearProperty(Configuration.JAEGER_SAMPLER_TYPE);
+    System.clearProperty(Configuration.JAEGER_SAMPLER_PARAM);
+
+    PrometheusMeterRegistry registry = (PrometheusMeterRegistry) io.micrometer.core.instrument.Metrics.globalRegistry
+        .getRegistries()
+        .iterator()
+        .next();
+
+    configuration.getTracer().buildSpan("theoperation").start().finish(100);
+    assertEquals(1, registry.find("jaeger:started_spans").counter().count(), 0);
+  }
+
   private void createSomeSpans(Tracer tracer) {
     for (int i = 0; i < 10; i++) {
       Span span = tracer.buildSpan("metricstest")