Saygın Doğu Saygın Doğu - 2 months ago 11
Scala Question

Compiling Scala Using Maven

I want to create a hello world application using maven.

here is my pom.xml:

<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>ColossusPlay</groupId>
<artifactId>ColossusPlay</artifactId>
<version>0.0.1-SNAPSHOT</version>
<build>
<sourceDirectory>src</sourceDirectory>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
<dependencies>
<dependency>
<groupId>com.tumblr</groupId>
<artifactId>colossus-metrics_2.10</artifactId>
<version>0.8.1-RC1</version>
</dependency>
</dependencies>
</project>


and here is my scala code:

object Main extends App{
println( "Helo World" )
}


when I run

mvn package


it generates a jar file in the target directory. Then what I want to be able to do is run that jar file using

scala target/ColossusPlay-0.0.1-SNAPSHOT.jar


However I get NullPointer Exception like this:

java.lang.NullPointerException
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at scala.reflect.internal.util.ScalaClassLoader$$anonfun$tryClass$1.apply(ScalaClassLoader.scala:43)
at scala.reflect.internal.util.ScalaClassLoader$$anonfun$tryClass$1.apply(ScalaClassLoader.scala:43)
at scala.util.control.Exception$Catch$$anonfun$opt$1.apply(Exception.scala:119)
at scala.util.control.Exception$Catch$$anonfun$opt$1.apply(Exception.scala:119)
at scala.util.control.Exception$Catch.apply(Exception.scala:103)
at scala.util.control.Exception$Catch.opt(Exception.scala:119)
at scala.reflect.internal.util.ScalaClassLoader$class.tryClass(ScalaClassLoader.scala:42)
at scala.reflect.internal.util.ScalaClassLoader$class.tryToInitializeClass(ScalaClassLoader.scala:39)
at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.tryToInitializeClass(ScalaClassLoader.scala:101)
at scala.reflect.internal.util.ScalaClassLoader$class.run(ScalaClassLoader.scala:63)
at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:101)
at scala.tools.nsc.CommonRunner$class.run(ObjectRunner.scala:22)
at scala.tools.nsc.JarRunner$.run(MainGenericRunner.scala:13)
at scala.tools.nsc.CommonRunner$class.runAndCatch(ObjectRunner.scala:29)
at scala.tools.nsc.JarRunner$.runJar(MainGenericRunner.scala:25)
at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:69)
at scala.tools.nsc.MainGenericRunner.run$1(MainGenericRunner.scala:87)
at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:98)
at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:103)
at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)


What am I missing?

Update:

The problem appears to be that the maven build does not see the source files. I tried to force it to have a build error writing nonesense to the source file but the mvn package still says build success. Additionaly when I examine the jar file, there isn't any class files inside. How can I make the maven see the source files.

Answer

You have to add a scale compiler plugin such sbt-compiler plugin

SBT compiler plugin

Example pom

 <plugin>
            <groupId>com.google.code.sbt-compiler-maven-plugin</groupId>
            <artifactId>sbt-compiler-maven-plugin</artifactId>
            <version>1.0.0-beta9</version>
            <executions>
                <execution>
                    <id>default-sbt-compile</id>
                    <goals>
                        <goal>compile</goal>
                        <goal>testCompile</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>

Using maven with scala in specific use case ( profiles, complex deployments, deep hierarchy ) is even better than pure sbt , but at the beginning is a bit tricky.

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