Add Spanner Leaderboard sample.

spanner/leaderboard/README.md

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+# Java Cloud Spanner Sample Leaderboard Application
+
+A leaderboard sample that uses the Cloud Spanner commit timestamp feature and demonstrates
+how to call the [Google Cloud Spanner API](https://cloud.google.com/spanner/docs/)
+using the [Google Cloud Client Library for Java](https://github.com/GoogleCloudPlatform/google-cloud-java).
+
+This sample requires [Java](https://www.java.com/en/download/) and [Maven](http://maven.apache.org/) for building the application.
+
+This sample includes extra directories `step5`, `step6`, and `step7` that contain partial versions of this sample application. These directories are intended to provide guidance as part of a separate Codelab walk-through where the application is built in the following stages
+that correspond to the steps in Codelab:
+
+* step5 - Create the sample database along with the tables Players and Scores.
+* step6 - Populate the Players and Scores tables with sample data.
+* step7 - Run sample queries including sorting the results by timestamp.
+
+If you only want to run the complete sample refer to the application in the `complete` directory.
+
+
+## Build and Run
+
+1.  **Follow the set-up instructions in [the documentation](https://cloud.google.com/java/docs/setup).**
+
+2.  Enable APIs for your project.
+    [Click here](https://console.cloud.google.com/flows/enableapi?apiid=spanner.googleapis.com&showconfirmation=true)
+    to visit Cloud Platform Console and enable the Google Cloud Spanner API.
+
+3.  Create a Cloud Spanner instance via the Cloud Plaform Console's
+    [Cloud Spanner section](http://console.cloud.google.com/spanner).
+
+4.  In a terminal shell, change directory to the version of the application you want to run:
+    ```
+    cd complete
+    ```
+
+5.  Run the following Maven command to build the application:
+    ```
+    mvn install -DskipTests
+    ```
+
+6.  Change directory into the `target` directory where the application's jar file gets built to.
+    ```
+    cd target
+    ```
+
+
+7. Run the Spanner Leaderboard sample with `java -jar leaderboard.jar` to see a list of available commands:
+    ```
+    @shell:~/.../target$ java -jar leaderboard.jar
+
+    Leaderboard 1.0.0
+    Usage:
+    java -jar leaderboard.jar <command> <instance_id> <database_id> [command_option]
+
+    Examples:
+    java -jar leaderboard.jar create my-instance example-db
+        - Create a sample Cloud Spanner database along with sample tables in your project.
+
+    java -jar leaderboard.jar insert my-instance example-db players
+        - Insert 100 sample Player records into the database.
+
+    java -jar leaderboard.jar insert my-instance example-db scores
+        - Insert sample score data into Scores sample Cloud Spanner database table.
+
+    java -jar leaderboard.jar query my-instance example-db
+        - Query players with top ten scores of all time.
+
+    java -jar leaderboard.jar query my-instance example-db 168
+        - Query players with top ten scores within a timespan specified in hours.
+
+    java -jar leaderboard.jar delete my-instance example-db
+        - Delete sample Cloud Spanner database.
+    ```
+
+    ```
+    $ java -jar leaderboard.jar create my-instance my-database
+    Created database [projects/arc-nl/instances/my-instance/databases/my-database]
+    ```

spanner/leaderboard/complete/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>com.google.codelabs</groupId>
+  <artifactId>leaderboard</artifactId>
+  <version>1.0-SNAPSHOT</version>
+
+  <name>leaderboard</name>
+  <!-- FIXME change it to the project's website -->
+  <url>http://www.example.com</url>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <maven.compiler.source>1.8</maven.compiler.source>
+    <maven.compiler.target>1.8</maven.compiler.target>
+  </properties>
+
+  <!--
+    The parent pom defines common style checks and testing strategies for our samples.
+    Removing or replacing it should not affect the execution of the samples in anyway.
+  -->
+  <parent>
+    <groupId>com.google.cloud.samples</groupId>
+    <artifactId>shared-configuration</artifactId>
+    <version>1.0.10</version>
+  </parent>
+
+  <dependencyManagement>
+    <dependencies>
+      <dependency>
+        <groupId>com.google.cloud</groupId>
+        <artifactId>google-cloud-bom</artifactId>
+        <version>0.73.0-alpha</version>
+        <type>pom</type>
+        <scope>import</scope>
+      </dependency>
+    </dependencies>
+  </dependencyManagement>
+  <dependencies>
+    <dependency>
+      <!-- Version auto-managed by BOM -->
+      <groupId>com.google.cloud</groupId>
+      <artifactId>google-cloud-spanner</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>4.13-beta-2</version>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>com.google.truth</groupId>
+      <artifactId>truth</artifactId>
+      <version>0.42</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <plugins>
+      <plugin>
+        <artifactId>maven-assembly-plugin</artifactId>
+        <version>2.5.5</version>
+        <configuration>
+          <finalName>leaderboard</finalName>
+          <descriptorRefs>
+            <descriptorRef>jar-with-dependencies</descriptorRef>
+          </descriptorRefs>
+          <archive>
+            <manifest>
+              <mainClass>com.google.codelabs.App</mainClass>
+            </manifest>
+          </archive>
+          <appendAssemblyId>false</appendAssemblyId>
+          <attach>false</attach>
+        </configuration>
+        <executions>
+          <execution>
+            <id>make-assembly</id>
+            <phase>package</phase>
+            <goals>
+              <goal>single</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-failsafe-plugin</artifactId>
+        <version>3.0.0-M3</version>
+      </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <version>3.0.0-M3</version>
+        <configuration>
+            <useSystemClassLoader>false</useSystemClassLoader>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>