Add autoconfiguration wrapper artifact

api/all/src/main/java/io/opentelemetry/api/GlobalOpenTelemetry.java

@@ -10,6 +10,8 @@
 import io.opentelemetry.context.propagation.ContextPropagators;
 import io.opentelemetry.spi.OpenTelemetryFactory;
 import io.opentelemetry.spi.trace.TracerProviderFactory;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
 import javax.annotation.Nullable;
 
 /**
@@ -31,6 +33,9 @@
  */
 public final class GlobalOpenTelemetry {
   private static final Object mutex = new Object();
+
+  private static final OpenTelemetry NO_OP = DefaultOpenTelemetry.builder().build();
+
   @Nullable private static volatile OpenTelemetry globalOpenTelemetry;
 
   private GlobalOpenTelemetry() {}
@@ -48,12 +53,14 @@ public static OpenTelemetry get() {
     if (globalOpenTelemetry == null) {
       synchronized (mutex) {
         if (globalOpenTelemetry == null) {
-          OpenTelemetryFactory openTelemetryFactory = Utils.loadSpi(OpenTelemetryFactory.class);
-          if (openTelemetryFactory != null) {
-            set(openTelemetryFactory.create());
-          } else {
-            set(DefaultOpenTelemetry.builder().build());
+
+          OpenTelemetry autoConfigured = maybeAutoConfigure();
+          if (autoConfigured != null) {
+            set(autoConfigured);
+            return autoConfigured;
           }
+
+          return NO_OP;
         }
       }
     }
@@ -115,4 +122,25 @@ public static Tracer getTracer(String instrumentationName, String instrumentatio
   public static ContextPropagators getPropagators() {
     return get().getPropagators();
   }
+
+  @Nullable
+  private static OpenTelemetry maybeAutoConfigure() {
+    final Class<?> openTelemetrySdkAutoConfiguration;
+    try {
+      openTelemetrySdkAutoConfiguration =
+          Class.forName("io.opentelemetry.sdk.autoconfigure.OpenTelemetrySdkAutoConfiguration");
+    } catch (ClassNotFoundException e) {
+      return null;
+    }
+
+    try {
+      Method initialize = openTelemetrySdkAutoConfiguration.getMethod("initialize");
+      return (OpenTelemetry) initialize.invoke(null);
+    } catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {
+      throw new IllegalStateException(
+          "OpenTelemetrySdkAutoConfiguration detected on classpath "
+              + "but could not invoke initialize method. This is a bug in OpenTelemetry.",
+          e);
+    }
+  }
 }

build.gradle

@@ -199,6 +199,7 @@ subprojects {
                     jsr305                      : "com.google.code.findbugs:jsr305:${findBugsJsr305Version}",
                     prometheus_client           : "io.prometheus:simpleclient:${prometheusVersion}",
                     prometheus_client_common    : "io.prometheus:simpleclient_common:${prometheusVersion}",
+                    prometheus_client_httpserver: "io.prometheus:simpleclient_httpserver:${prometheusVersion}",
                     protobuf                    : "com.google.protobuf:protobuf-java",
                     protobuf_util               : "com.google.protobuf:protobuf-java-util",
                     zipkin_reporter             : "io.zipkin.reporter2:zipkin-reporter",

exporters/prometheus/build.gradle

@@ -9,9 +9,8 @@ description = 'OpenTelemetry Prometheus Exporter'
 ext.moduleName = "io.opentelemetry.exporter.prometheus"
 
 dependencies {
-    api project(':sdk:metrics')
-
-    implementation libraries.prometheus_client
+    api project(':sdk:metrics'),
+            libraries.prometheus_client
 
     testImplementation libraries.prometheus_client_common,
             libraries.guava

sdk-extensions/autoconfigure/build.gradle

@@ -0,0 +1,27 @@
+plugins {
+    id "java-library"
+    id "maven-publish"
+
+    id "ru.vyarus.animalsniffer"
+}
+
+description = 'OpenTelemetry SDK Auto-configuration'
+ext.moduleName = "io.opentelemetry.sdk.autoconfigure"
+
+dependencies {
+    api project(':sdk:all'),
+            project(':sdk:metrics')
+
+    implementation project(':extensions:trace-propagators')
+
+    compileOnly project(':exporters:jaeger')
+    compileOnly project(':exporters:jaeger-thrift')
+    compileOnly project(':exporters:logging')
+    compileOnly project(':exporters:otlp:all')
+    compileOnly project(':exporters:otlp:metrics')
+
+    compileOnly project(':exporters:prometheus')
+    compileOnly libraries.prometheus_client_httpserver
+
+    compileOnly project(':exporters:zipkin')
+}

sdk-extensions/autoconfigure/src/main/java/io/opentelemetry/sdk/autoconfigure/ConfigProperties.java

@@ -0,0 +1,108 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.autoconfigure;
+
+import java.util.AbstractMap;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Properties;
+import java.util.stream.Collectors;
+import javax.annotation.Nullable;
+
+class ConfigProperties {
+
+  static ConfigProperties get() {
+    return new ConfigProperties(System.getProperties(), System.getenv());
+  }
+
+  private final Map<String, String> config;
+
+  private ConfigProperties(Properties systemProperties, Map<String, String> environmentVariables) {
+    Map<String, String> config = new HashMap<>();
+    environmentVariables.forEach(
+        (name, value) -> {
+          config.put(name.toLowerCase(Locale.ROOT).replace('_', '.'), value);
+        });
+    systemProperties.forEach(
+        (key, value) -> {
+          config.put(((String) key).toLowerCase(Locale.ROOT), (String) value);
+        });
+
+    this.config = config;
+  }
+
+  @Nullable
+  String getString(String name) {
+    return config.get(name);
+  }
+
+  @Nullable
+  Integer getInt(String name) {
+    try {
+      // Null will throw NumberFormatException too.
+      return Integer.parseInt(config.get(name));
+    } catch (NumberFormatException ex) {
+      return null;
+    }
+  }
+
+  @Nullable
+  Long getLong(String name) {
+    try {
+      // Null will throw NumberFormatException too.
+      return Long.parseLong(config.get(name));
+    } catch (NumberFormatException ex) {
+      return null;
+    }
+  }
+
+  /**
+   * Get a double property from the config or {@code null} if it cannot be found or it has a wrong
+   * type.
+   */
+  @Nullable
+  Double getDouble(String name) {
+    try {
+      return Double.parseDouble(config.get(name));
+    } catch (NumberFormatException | NullPointerException ex) {
+      return null;
+    }
+  }
+
+  List<String> getCommaSeparatedValues(String name) {
+    String value = config.get(name);
+    if (value == null) {
+      return Collections.emptyList();
+    }
+    return Arrays.stream(value.split(","))
+        .map(String::trim)
+        .filter(s -> !s.isEmpty())
+        .collect(Collectors.toList());
+  }
+
+  Map<String, String> getCommaSeparatedMap(String name) {
+    return getCommaSeparatedValues(name).stream()
+        .map(
+            keyValuePair ->
+                Arrays.stream(keyValuePair.split("=", 2))
+                    .map(String::trim)
+                    .filter(s -> !s.isEmpty())
+                    .collect(Collectors.toList()))
+        .map(
+            splitKeyValuePairs ->
+                new AbstractMap.SimpleImmutableEntry<>(
+                    splitKeyValuePairs.get(0), splitKeyValuePairs.get(1)))
+        .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
+  }
+
+  boolean getBoolean(String name) {
+    return Boolean.parseBoolean(config.get(name));
+  }
+}