Move stats and tags packages to opencensus-api to prepare for release. (#723)

1 files changed, 95 insertions, 0 deletions

diff --git a/api/src/main/java/io/opencensus/stats/Stats.java b/api/src/main/java/io/opencensus/stats/Stats.java
new file mode 100644
index 00000000..016455e9
--- /dev/null
+++ b/api/src/main/java/io/opencensus/stats/Stats.java
@@ -0,0 +1,95 @@
+/*
+ * Copyright 2016-17, 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.stats;
+
+import com.google.common.annotations.VisibleForTesting;
+import io.opencensus.internal.Provider;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+/** Class for accessing the default {@link StatsComponent}. */
+public final class Stats {
+  private static final Logger logger = Logger.getLogger(Stats.class.getName());
+
+  private static final StatsComponent statsComponent =
+      loadStatsComponent(StatsComponent.class.getClassLoader());
+
+  /** Returns the default {@link StatsRecorder}. */
+  public static StatsRecorder getStatsRecorder() {
+    return statsComponent.getStatsRecorder();
+  }
+
+  /** Returns the default {@link ViewManager}. */
+  public static ViewManager getViewManager() {
+    return statsComponent.getViewManager();
+  }
+
+  /**
+   * Returns the current {@code StatsCollectionState}.
+   *
+   * <p>When no implementation is available, {@code getState} always returns {@link
+   * StatsCollectionState#DISABLED}.
+   *
+   * @return the current {@code StatsCollectionState}.
+   */
+  public static StatsCollectionState getState() {
+    return statsComponent.getState();
+  }
+
+  /**
+   * Sets the current {@code StatsCollectionState}.
+   *
+   * <p>When no implementation is available, {@code setState} has no effect.
+   *
+   * @param state the new {@code StatsCollectionState}.
+   */
+  public static void setState(StatsCollectionState state) {
+    statsComponent.setState(state);
+  }
+
+  // Any provider that may be used for StatsComponent can be added here.
+  @VisibleForTesting
+  static StatsComponent loadStatsComponent(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.stats.StatsComponentImpl", true, classLoader),
+          StatsComponent.class);
+    } catch (ClassNotFoundException e) {
+      logger.log(
+          Level.FINE,
+          "Couldn't load full implementation for StatsComponent, 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.stats.StatsComponentImplLite", true, classLoader),
+          StatsComponent.class);
+    } catch (ClassNotFoundException e) {
+      logger.log(
+          Level.FINE,
+          "Couldn't load lite implementation for StatsComponent, now using "
+              + "default implementation for StatsComponent.",
+          e);
+    }
+    return NoopStats.newNoopStatsComponent();
+  }
+
+  private Stats() {}
+}