add gRPC java samples (GoogleCloudPlatform#419)

* add gRPC java samples
* remove build directories
* update code to address review comments

Author: wlu2016

endpoints/bookstore-grpc/Dockerfile

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+# https://github.com/GoogleCloudPlatform/openjdk-runtime
+FROM gcr.io/google_appengine/openjdk8
+
+RUN echo 'deb http://httpredir.debian.org/debian jessie-backports main' > /etc/apt/sources.list.d/jessie-backports.list \
+    && apt-get update \
+    && apt-get install --no-install-recommends -y -q ca-certificates \
+    && apt-get -y -q upgrade \
+    && apt-get install --no-install-recommends -y openjdk-8-jre-headless \
+    && rm -rf /var/lib/apt/lists/*
+
+ADD ./server/build/libs/server.jar /bookstore/server.jar
+
+EXPOSE 8000
+
+ENTRYPOINT ["java", "-jar", "/bookstore/server.jar"]

endpoints/bookstore-grpc/README.md

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+# Google Cloud Endpoints Bookstore App in Java
+
+## Prerequisites
+
+* [Java 8](http://openjdk.java.net/install/)
+* [Docker](https://www.docker.com/products/docker)
+
+## Building and Running the Server
+
+The Java Bookstore gRPC example is built using Gradle:
+
+    ./gradlew build
+
+To run the Java server and client locally:
+
+    # Start the server (listens on port 8000 by default)
+    java -jar ./server/build/libs/server.jar
+
+    # Run the client (connects to localhost:8000 by default)
+    java -jar ./client/build/libs/client.jar

endpoints/bookstore-grpc/api/build.gradle

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+// Copyright 2016 Google Inc. All Rights Reserved.
+//
+// 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.
+//
+////////////////////////////////////////////////////////////////////////////////
+
+apply plugin: 'java'
+apply plugin: 'com.google.protobuf'
+
+buildscript {
+  repositories {
+    mavenCentral()
+  }
+  dependencies {
+    classpath 'com.google.protobuf:protobuf-gradle-plugin:0.8.0'
+
+  }
+}
+
+dependencies {
+  repositories {
+    mavenCentral()
+  }
+  compile 'io.grpc:grpc-netty:1.0.1'
+  compile 'io.grpc:grpc-protobuf:1.0.1'
+  compile 'io.grpc:grpc-stub:1.0.1'
+}
+
+protobuf {
+  protoc {
+    artifact = 'com.google.protobuf:protoc:3.0.2'
+  }
+
+  plugins {
+    grpc {
+      artifact = 'io.grpc:protoc-gen-grpc-java:1.0.1'
+    }
+  }
+  generateProtoTasks {
+    all()*.plugins {
+      grpc {}
+    }
+  }
+}

endpoints/bookstore-grpc/api/src/main/proto/bookstore.proto

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+// Copyright 2016 Google Inc. All Rights Reserved.
+//
+// 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.
+//
+////////////////////////////////////////////////////////////////////////////////
+
+syntax = "proto3";
+
+package endpoints.examples.bookstore;
+
+option java_multiple_files = true;
+option java_outer_classname = "BookstoreProto";
+option java_package = "com.google.endpoints.examples.bookstore";
+
+
+import "google/protobuf/empty.proto";
+
+// A simple Bookstore API.
+//
+// The API manages shelves and books resources. Shelves contain books.
+service Bookstore {
+  // Returns a list of all shelves in the bookstore.
+  rpc ListShelves(google.protobuf.Empty) returns (ListShelvesResponse) {}
+  // Creates a new shelf in the bookstore.
+  rpc CreateShelf(CreateShelfRequest) returns (Shelf) {}
+  // Returns a specific bookstore shelf.
+  rpc GetShelf(GetShelfRequest) returns (Shelf) {}
+  // Deletes a shelf, including all books that are stored on the shelf.
+  rpc DeleteShelf(DeleteShelfRequest) returns (google.protobuf.Empty) {}
+  // Returns a list of books on a shelf.
+  rpc ListBooks(ListBooksRequest) returns (ListBooksResponse) {}
+  // Creates a new book.
+  rpc CreateBook(CreateBookRequest) returns (Book) {}
+  // Returns a specific book.
+  rpc GetBook(GetBookRequest) returns (Book) {}
+  // Deletes a book from a shelf.
+  rpc DeleteBook(DeleteBookRequest) returns (google.protobuf.Empty) {}
+}
+
+// A shelf resource.
+message Shelf {
+  // A unique shelf id.
+  int64 id = 1;
+  // A theme of the shelf (fiction, poetry, etc).
+  string theme = 2;
+}
+
+// A book resource.
+message Book {
+  // A unique book id.
+  int64 id = 1;
+  // An author of the book.
+  string author = 2;
+  // A book title.
+  string title = 3;
+}
+
+// Response to ListShelves call.
+message ListShelvesResponse {
+  // Shelves in the bookstore.
+  repeated Shelf shelves = 1;
+}
+
+// Request message for CreateShelf method.
+message CreateShelfRequest {
+  // The shelf resource to create.
+  Shelf shelf = 1;
+}
+
+// Request message for GetShelf method.
+message GetShelfRequest {
+  // The ID of the shelf resource to retrieve.
+  int64 shelf = 1;
+}
+
+// Request message for DeleteShelf method.
+message DeleteShelfRequest {
+  // The ID of the shelf to delete.
+  int64 shelf = 1;
+}
+
+// Request message for ListBooks method.
+message ListBooksRequest {
+  // ID of the shelf which books to list.
+  int64 shelf = 1;
+}
+
+// Response message to ListBooks method.
+message ListBooksResponse {
+  // The books on the shelf.
+  repeated Book books = 1;
+}
+
+// Request message for CreateBook method.
+message CreateBookRequest {
+  // The ID of the shelf on which to create a book.
+  int64 shelf = 1;
+  // A book resource to create on the shelf.
+  Book book = 2;
+}
+
+// Request message for GetBook method.
+message GetBookRequest {
+  // The ID of the shelf from which to retrieve a book.
+  int64 shelf = 1;
+  // The ID of the book to retrieve.
+  int64 book = 2;
+}
+
+// Request message for DeleteBook method.
+message DeleteBookRequest {
+  // The ID of the shelf from which to delete a book.
+  int64 shelf = 1;
+  // The ID of the book to delete.
+  int64 book = 2;
+}

endpoints/bookstore-grpc/build.gradle

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+subprojects {
+  apply plugin: 'java'
+
+  repositories {
+    mavenCentral()
+  }
+}

endpoints/bookstore-grpc/client/build.gradle

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+// Copyright 2016 Google Inc. All Rights Reserved.
+//
+// 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.
+//
+////////////////////////////////////////////////////////////////////////////////
+
+apply plugin: 'application'
+
+mainClassName = "com.google.endpoints.examples.bookstore.BookstoreClient"
+
+jar {
+  manifest {
+    attributes "Main-Class": "$mainClassName"
+  }
+  from {
+    configurations.compile.collect { it.isDirectory() ? it : zipTree(it) }
+  }
+}
+
+dependencies {
+  compile project(':api')
+  compile 'commons-cli:commons-cli:1.3'
+}