Snippet: Mixing Scala, Java in a Maven Project

March 23rd, 2012 by

Having just returned from the Atlassian Camp 2012 I just toyed around with Java and Scala and wanted to share the following snippet that demonstrates how to mix code from both languages in a Maven project using the maven-scala-plugin.


 

Setting up the Maven Project

First create a new Maven project in your IDE or by running mvn archetype:generate.

In the next step, add the dependency for scala-library and the scala maven repositories to your pom.xml and hook the maven-scala-plugin to Maven’s lifecycle. My pom.xml finally looks like this one:

<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.hascode.tutorial</groupId>
<artifactId>scala-maven-tutorial</artifactId>
<version>0.0.1-SNAPSHOT</version>
<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
    <dependency>
        <groupId>org.scala-lang</groupId>
        <artifactId>scala-library</artifactId>
        <version>2.9.1</version>
    </dependency>
</dependencies>
<repositories>
    <repository>
        <id>scala-tools.org</id>
        <name>Scala-tools Maven2 Repository</name>
        <url>http://scala-tools.org/repo-releases</url>
    </repository>
</repositories>
<pluginRepositories>
    <pluginRepository>
        <id>scala-tools.org</id>
        <name>Scala-tools Maven2 Repository</name>
        <url>http://scala-tools.org/repo-releases</url>
    </pluginRepository>
</pluginRepositories>
<build>
    <pluginManagement>
        <plugins>
            <plugin>
                <groupId>org.scala-tools</groupId>
                <artifactId>maven-scala-plugin</artifactId>
                <version>2.9.1</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.0.2</version>
            </plugin>
        </plugins>
    </pluginManagement>
    <plugins>
        <plugin>
            <groupId>org.scala-tools</groupId>
            <artifactId>maven-scala-plugin</artifactId>
            <executions>
                <execution>
                    <id>scala-compile-first</id>
                    <phase>process-resources</phase>
                    <goals>
                        <goal>add-source</goal>
                        <goal>compile</goal>
                    </goals>
                </execution>
                <execution>
                    <id>scala-test-compile</id>
                    <phase>process-test-resources</phase>
                    <goals>
                        <goal>testCompile</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <executions>
                <execution>
                    <phase>compile</phase>
                    <goals>
                        <goal>compile</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>
</project>

Finally add these both source folders for your Scala code to your project directory:

  • src/main/scala
  • src/test/scala

Writing some code

Now we need some code for both languages .. first our Java class providing a service that returns a simple string

package com.hascode.tutorial.service;
 
public class SomeJavaService {
	public String getInfo() {
		return "this is from java..";
	}
}

Afterwards we’re creating our scala class in src/main/scala

package com.hascode.tutorial
import com.hascode.tutorial.service._
 
object Main {
	def main(args: Array[String]) {
		println("We're running scala..")
		val service = new SomeJavaService
		println(service.getInfo())
	}
 }

Running the Application

Finally build and run the application using Maven..

mvn clean package exec:java -Dexec.mainClass=com.hascode.tutorial.Main

This should yield the following output ..

We're running scala..
this is from java..

Tutorial Sources

I have put the source from this tutorial on my Bitbucket repository – download it there or check it out using Mercurial:

hg clone https://bitbucket.org/hascode/scala-maven-tutorial

Resources

package com.hascode.tutorial
import com.hascode.tutorial.service._

object Main {
def main(args: Array[String]) {
println(“We’re running scala..”)
val service = new SomeJavaService
println(service.getInfo())
}
}

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