specify spark version (#1224)

doc/jvm/index.md

@@ -11,9 +11,9 @@ Currently, XGBoost4J only support installation from source. Building XGBoost4J u
 
 Before you install XGBoost4J, you need to define environment variable `JAVA_HOME` as your JDK directory to ensure that your compiler can find `jni.h` correctly, since XGBoost4J relies on JNI to implement the interaction between the JVM and native libraries.
 
-After your `JAVA_HOME` is defined correctly, it is as simple as run `mvn package` under jvm-packages directory to install XGBoost4J.
+After your `JAVA_HOME` is defined correctly, it is as simple as run `mvn package` under jvm-packages directory to install XGBoost4J. You can also skip the tests by running `mvn -DskipTests=true package`, if you are sure about the correctness of your local setup.
 
-NOTE: XGBoost4J requires to run with Spark 1.6 or newer
+XGBoost4J-Spark which integrates XGBoost with Spark requires to run with Spark 1.6 or newer (the default version is 1.6.1). You can build XGBoost4J-Spark as a component of XGBoost4J by running `mvn package` or specifying the spark version by `mvn -Dspark.version=1.6.0 package`.
 
 Contents
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jvm-packages/pom.xml

@@ -23,6 +23,18 @@
         <module>xgboost4j-spark</module>
         <module>xgboost4j-flink</module>
     </modules>
+    <profiles>
+        <profile>
+            <id>spark-1.x</id>
+            <activation>
+                <activeByDefault>true</activeByDefault>
+            </activation>
+            <properties>
+                <spark.version>1.6.1</spark.version>
+                <scala.binary.version>2.10</scala.binary.version>
+            </properties>
+        </profile>
+    </profiles>
     <build>
         <plugins>
             <plugin>

jvm-packages/xgboost4j-spark/pom.xml

@@ -28,8 +28,8 @@
         </dependency>
         <dependency>
             <groupId>org.apache.spark</groupId>
-            <artifactId>spark-mllib_2.10</artifactId>
-            <version>1.6.1</version>
+            <artifactId>spark-mllib_${scala.binary.version}</artifactId>
+            <version>${spark.version}</version>
         </dependency>
     </dependencies>
 </project>