1 files changed, 96 insertions, 0 deletions
diff --git a/api/src/main/java/io/opencensus/metrics/Metrics.java b/api/src/main/java/io/opencensus/metrics/Metrics.java
new file mode 100644
index 00000000..521fbd08
--- /dev/null
+++ b/api/src/main/java/io/opencensus/metrics/Metrics.java
@@ -0,0 +1,96 @@
+/*
+ * Copyright 2018, OpenCensus 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.opencensus.metrics;
+
+import io.opencensus.common.ExperimentalApi;
+import io.opencensus.internal.DefaultVisibilityForTesting;
+import io.opencensus.internal.Provider;
+import io.opencensus.metrics.export.ExportComponent;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import javax.annotation.Nullable;
+
+/**
+ * Class for accessing the default {@link MetricsComponent}.
+ *
+ * @since 0.16
+ */
+@ExperimentalApi
+public final class Metrics {
+  private static final Logger logger = Logger.getLogger(Metrics.class.getName());
+  private static final MetricsComponent metricsComponent =
+      loadMetricsComponent(MetricsComponent.class.getClassLoader());
+
+  /**
+   * Returns the global {@link ExportComponent}.
+   *
+   * @return the global {@code ExportComponent}.
+   * @since 0.16
+   */
+  public static ExportComponent getExportComponent() {
+    return metricsComponent.getExportComponent();
+  }
+
+  /**
+   * Returns the global {@link MetricRegistry}.
+   *
+   * <p>This {@code MetricRegistry} is already added to the global {@link
+   * io.opencensus.metrics.export.MetricProducerManager}.
+   *
+   * @return the global {@code MetricRegistry}.
+   * @since 0.16
+   */
+  public static MetricRegistry getMetricRegistry() {
+    return metricsComponent.getMetricRegistry();
+  }
+
+  // Any provider that may be used for MetricsComponent can be added here.
+  @DefaultVisibilityForTesting
+  static MetricsComponent loadMetricsComponent(@Nullable ClassLoader classLoader) {
+    try {
+      // Call Class.forName with literal string name of the class to help shading tools.
+      return Provider.createInstance(
+          Class.forName(
+              "io.opencensus.impl.metrics.MetricsComponentImpl", /*initialize=*/ true, classLoader),
+          MetricsComponent.class);
+    } catch (ClassNotFoundException e) {
+      logger.log(
+          Level.FINE,
+          "Couldn't load full implementation for MetricsComponent, now trying to load lite "
+              + "implementation.",
+          e);
+    }
+    try {
+      // Call Class.forName with literal string name of the class to help shading tools.
+      return Provider.createInstance(
+          Class.forName(
+              "io.opencensus.impllite.metrics.MetricsComponentImplLite",
+              /*initialize=*/ true,
+              classLoader),
+          MetricsComponent.class);
+    } catch (ClassNotFoundException e) {
+      logger.log(
+          Level.FINE,
+          "Couldn't load lite implementation for MetricsComponent, now using default "
+              + "implementation for MetricsComponent.",
+          e);
+    }
+    return MetricsComponent.newNoopMetricsComponent();
+  }
+
+  private Metrics() {}
+}