Spark - maven clean install: How to compile both Java and Scala classes

Question

I have a Spark project, which has both .scala and .java files. I am trying to compile both type of classes through maven build. However, when I ran "mvn clean install", it only creates .class file for Java, not Scala. The following is my pom.xml, am I missing anything? Thank you very much!

PS. I can only build Scala classes through eclipse IDE, but this is very inconvenient and bad for automatic build... so I am looking for a better solution using maven command line. Thanks!

<?xml version="1.0"?>
<project
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
    xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>my-project</groupId>
        <artifactId>my-project</artifactId>
        <version>1.2-SNAPSHOT</version>
    </parent>
    <groupId>my-project-module1</groupId>
    <artifactId>my-project-module1</artifactId>
    <name>my-project-module1</name>
    <url>http://maven.apache.org</url>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>
    <dependencies>
        <dependency>
            <groupId>my-project</groupId>
            <artifactId>my-project-module0</artifactId>
            <version>${project.version}</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
        </dependency>
        <dependency>
            <groupId>org.scala-lang</groupId>
            <artifactId>scala-library</artifactId>
            <version>2.10.3</version>
        </dependency>
        <dependency>
            <groupId>org.scalatest</groupId>
            <artifactId>scalatest_2.10</artifactId>
            <version>2.0.M5b</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.thoughtworks.xstream</groupId>
            <artifactId>xstream</artifactId>
            <version>1.4.4</version>
        </dependency>
        <dependency>
            <groupId>com.google.code.gson</groupId>
            <artifactId>gson</artifactId>
            <version>2.2.4</version>
        </dependency>
        <dependency>
            <groupId>nz.ac.waikato.cms.weka</groupId>
            <artifactId>weka-stable</artifactId>
            <version>3.6.6</version>
            <exclusions>
                <exclusion>
                    <artifactId>java-cup</artifactId>
                    <groupId>
      net.sf.squirrel-sql.thirdparty-non-maven
     </groupId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-client</artifactId>
            <version>2.4.0</version>
            <exclusions>
                <exclusion>
                    <artifactId>zookeeper</artifactId>
                    <groupId>org.apache.zookeeper</groupId>
                </exclusion>
                <exclusion>
                    <artifactId>guava</artifactId>
                    <groupId>com.google.guava</groupId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.eclipse.jetty</groupId>
            <artifactId>jetty-servlet</artifactId>
            <version>8.1.14.v20131031</version>
        </dependency>
        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
            <version>14.0.1</version>
        </dependency>

        <dependency>
            <groupId>net.sourceforge.argparse4j</groupId>
            <artifactId>argparse4j</artifactId>
            <version>0.4.3</version>
        </dependency>
        <dependency>
            <groupId>com.amazonaws</groupId>
            <artifactId>aws-java-sdk</artifactId>
            <version>1.9.1</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.16</version>
        </dependency>
        <dependency>
            <groupId>com.github.scopt</groupId>
            <artifactId>scopt_2.10</artifactId>
            <version>3.2.0</version>
        </dependency>
        <dependency>
            <groupId>org.apache.spark</groupId>
            <artifactId>spark-mllib_2.10</artifactId>
            <version>1.3.1</version>
        </dependency>
    </dependencies>
</project>

Answer 1

This is actually very easy. you need to add a new build plugin:

<plugins>
...
            <plugin>
                <groupId>net.alchim31.maven</groupId>
                <artifactId>scala-maven-plugin</artifactId>
                <version>3.2.1</version>
                <configuration>
                    <recompileMode>incremental</recompileMode>
                    <args>
                        <arg>-target:jvm-1.7</arg>
                    </args>
                    <javacArgs>
                        <javacArg>-source</javacArg>
                        <javacArg>1.7</javacArg>
                        <javacArg>-target</javacArg>
                        <javacArg>1.7</javacArg>
                    </javacArgs>
                </configuration>
                <executions>
                    <execution>
                        <id>scala-compile</id>
                        <phase>process-resources</phase>
                        <goals>
                            <goal>compile</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>scala-test-compile</id>
                        <phase>process-test-resources</phase>
                        <goals>
                            <goal>testCompile</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
</plugins>

This will compile your java and scala classes at the same time. Here's a slightly more detailed description:

https://itellity.wordpress.com/2014/08/21/mixing-scala-and-java-in-a-maven-project/