feat: add channel pooling

stack-info: PR: #9692, branch: igorbernstein2/stack/5

Author: igorbernstein2

bigtable/bigtable-proxy/src/main/java/com/google/cloud/bigtable/examples/proxy/channelpool/ChannelFactory.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2019 Google LLC
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google LLC nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+// Copied from
+// https://github.com/googleapis/sdk-platform-java/blob/a333b0709023c971f12a85e5287b6d77d1b57c48/gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/ChannelFactory.java
+// Changes:
+// - package name
+// - removed InternalApi annotation
+
+package com.google.cloud.bigtable.examples.proxy.channelpool;
+
+import io.grpc.ManagedChannel;
+import java.io.IOException;
+
+/**
+ * This interface represents a factory for creating one ManagedChannel
+ *
+ * <p>This is public only for technical reasons, for advanced usage.
+ */
+public interface ChannelFactory {
+  ManagedChannel createSingleChannel() throws IOException;
+}