Add metrics exporter

build.gradle

@@ -19,6 +19,7 @@ subprojects {
     ext {
         autoValueVersion = '1.7.4'
         googleCloudVersion = '1.0.2'
+        cloudMonitoringVersion = '2.0.1'
         openTelemetryVersion = '0.7.0'
         junitVersion = '4.13'
         opentelemetryOperationsVersion = "0.7.1"  // CURRENT_RELEASE_VERSION
@@ -29,6 +30,7 @@ subprojects {
                 google_cloud_core            : "com.google.cloud:google-cloud-core:${googleCloudVersion}",
                 google_cloud_grpc            : "com.google.api.grpc:grpc-google-cloud-trace-v2:${googleCloudVersion}",
                 google_cloud_trace           : "com.google.cloud:google-cloud-trace:${googleCloudVersion}",
+                google_cloud_monitoring      : "com.google.cloud:google-cloud-monitoring:${cloudMonitoringVersion}",
                 opentelemetry_api            : "io.opentelemetry:opentelemetry-api:${openTelemetryVersion}",
                 opentelemetry_sdk            : "io.opentelemetry:opentelemetry-sdk:${openTelemetryVersion}",
                 opentelemetry_operations_java: "com.google.cloud.opentelemetry:exporter-trace:${opentelemetryOperationsVersion}"

exporters/metrics/build.gradle

@@ -0,0 +1,12 @@
+description = 'Cloud Monitoring Exporter for OpenTelemetry'
+
+dependencies {
+    api(libraries.auto_value_annotations)
+    annotationProcessor(libraries.auto_value)
+    api(libraries.opentelemetry_api)
+    api(libraries.opentelemetry_sdk)
+    api(libraries.google_cloud_core)
+    api(libraries.google_cloud_monitoring)
+    api(libraries.google_cloud_grpc)
+    testImplementation(testLibraries.junit)
+}

exporters/metrics/src/main/java/com.google.cloud.opentelemetry.metric/MetricConfiguration.java

@@ -0,0 +1,98 @@
+package com.google.cloud.opentelemetry.metric;
+
+import com.google.auth.Credentials;
+import com.google.auto.value.AutoValue;
+import com.google.cloud.ServiceOptions;
+import com.google.cloud.monitoring.v3.MetricServiceClient;
+import com.google.cloud.monitoring.v3.stub.MetricServiceStub;
+import com.google.common.base.Preconditions;
+import com.google.common.base.Strings;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+/** Configurations for {@link MetricExporter}. */
+@AutoValue
+@Immutable
+public abstract class MetricConfiguration {
+
+    private static final String DEFAULT_PROJECT_ID =
+            Strings.nullToEmpty(ServiceOptions.getDefaultProjectId());
+    private static final boolean DEFAULT_ADD_UNIQUE_IDENTIFIER = false;
+
+    MetricConfiguration() {}
+
+    /**
+     * Returns the {@link Credentials}.
+     *
+     * @return the {@code Credentials}.
+     */
+    @Nullable
+    public abstract Credentials getCredentials();
+
+    /**
+     * Returns the cloud project id.
+     *
+     * @return the cloud project id.
+     */
+    public abstract String getProjectId();
+
+    /**
+     * Returns the client.
+     *
+     * @return the client.
+     */
+    public abstract MetricServiceClient getClient();
+
+    /**
+     * Returns whether a unique identifier will be added.
+     *
+     * @return whether a unique identifier will be added.
+     */
+    public abstract boolean getAddUniqueIdentifier();
+
+    /**
+     * Returns a MetricsServiceStub instance used to make RPC calls.
+     *
+     * @return the metrics service stub.
+     */
+    @Nullable
+    public abstract MetricServiceStub getMetricServiceStub();
+
+    public static Builder builder() {
+        return new AutoValue_MetricConfiguration.Builder();
+    }
+
+    /** Builder for {@link MetricConfiguration}. */
+    @AutoValue.Builder
+    public abstract static class Builder {
+
+        Builder() {}
+
+        abstract String getProjectId();
+
+        abstract MetricServiceClient getClient();
+
+        abstract boolean getAddUniqueIdentifier();
+
+        abstract MetricConfiguration autoBuild();
+
+        public abstract Builder setProjectId(String newProjectId);
+
+        public abstract Builder setClient(MetricServiceClient newClient);
+
+        /**
+         * Builds a {@link MetricConfiguration}.
+         *
+         * @return a {@code MetricsConfiguration}.
+         */
+        public MetricConfiguration build() {
+            Preconditions.checkArgument(
+                    !Strings.isNullOrEmpty(getProjectId()),
+                    "Cannot find a project ID from either configurations or application default.");
+
+            return autoBuild();
+        }
+    }
+
+}