[HWKMETRICS-74] forgot to include VoidSubscriber in previous commit

core/metrics-core-impl/src/main/java/org/hawkular/metrics/core/impl/cassandra/VoidSubscriber.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2014-2015 Red Hat, Inc. and/or its affiliates
+ * and other contributors as indicated by the @author tags.
+ *
+ * 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 org.hawkular.metrics.core.impl.cassandra;
+
+import rx.Subscriber;
+
+/**
+ * A subscriber that is intended for use with an Observable that does not emit any items. A common use case for this
+ * is inserting data into the database. When inserting rows into Cassandra for example, the driver returns a result set
+ * which has no rows. In general we are only interested in whether or not the query completed successfully. Upon
+ * completion of the insert request, {@link #onCompleted()} will be invoked. If there is an time out or other error
+ * performing the operation, then {@link #onError(Throwable)} is invoked.
+ *
+ * @author jsanda
+ */
+public class VoidSubscriber<T> extends Subscriber<T> {
+
+    private Subscriber<? super Void> subscriber;
+
+    /**
+     * @param subscriber The original Subscriber to which calls are delegated.
+     */
+    public VoidSubscriber(Subscriber<? super Void> subscriber) {
+        this.subscriber = subscriber;
+    }
+
+    @Override
+    public void onCompleted() {
+        subscriber.onCompleted();
+    }
+
+    @Override
+    public void onError(Throwable e) {
+        subscriber.onError(e);
+    }
+
+    @Override
+    public void onNext(T t) {
+    }
+}