added checkstyle

s3/pom.xml

@@ -26,4 +26,28 @@
             <scope>provided</scope>
     </dependency>
    </dependencies>
+<build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-checkstyle-plugin</artifactId>
+        <version>2.15</version>
+        <configuration>
+          <consoleOutput>true</consoleOutput>
+          <configLocation>../checkstyle.xml</configLocation>
+          <failOnViolation>true</failOnViolation>
+          <failsOnError>true</failsOnError>
+        </configuration>
+        <executions>
+          <execution>
+            <id>validate</id>
+            <phase>validate</phase>
+            <goals>
+              <goal>checkstyle</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
 </project>