Maven not building Scala project correctly - scala

Question

Problem
I got a Maven - Scala project. It compiles etc. when I want to build it in IntelliJ it works but the output jar is empty except a pom.xml.
When a build the whole project via command line with mvn scala:compile I get the following errors:
[INFO] Compiling 67 source files to /Users/my.name/Documents/company/util/util/target/classes at 1555483575272
[ERROR] error: scala.reflect.internal.MissingRequirementError: object java.lang.Object in compiler mirror not found.
[ERROR] at scala.reflect.internal.MissingRequirementError$.signal(MissingRequirementError.scala:17)
[ERROR] at scala.reflect.internal.MissingRequirementError$.notFound(MissingRequirementError.scala:18)
[ERROR] at scala.reflect.internal.Mirrors$RootsBase.getModuleOrClass(Mirrors.scala:53)
[ERROR] at scala.reflect.internal.Mirrors$RootsBase.getModuleOrClass(Mirrors.scala:45)
[ERROR] at scala.reflect.internal.Mirrors$RootsBase.getModuleOrClass(Mirrors.scala:45)
[ERROR] at scala.reflect.internal.Mirrors$RootsBase.getModuleOrClass(Mirrors.scala:66)
[ERROR] at scala.reflect.internal.Mirrors$RootsBase.getClassByName(Mirrors.scala:102)
[ERROR] at scala.reflect.internal.Mirrors$RootsBase.getRequiredClass(Mirrors.scala:105)
[ERROR] at scala.reflect.internal.Definitions$DefinitionsClass.ObjectClass$lzycompute(Definitions.scala:257)
[ERROR] at scala.reflect.internal.Definitions$DefinitionsClass.ObjectClass(Definitions.scala:257)
[ERROR] at scala.reflect.internal.Definitions$DefinitionsClass.init(Definitions.scala:1394)
[ERROR] at scala.tools.nsc.Global$Run.<init>(Global.scala:1215)
[ERROR] at scala.tools.nsc.Driver.doCompile(Driver.scala:31)
[ERROR] at scala.tools.nsc.MainClass.doCompile(Main.scala:23)
[ERROR] at scala.tools.nsc.Driver.process(Driver.scala:51)
[ERROR] at scala.tools.nsc.Driver.main(Driver.scala:64)
[ERROR] at scala.tools.nsc.Main.main(Main.scala)
[ERROR] at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[ERROR] at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[ERROR] at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[ERROR] at java.base/java.lang.reflect.Method.invoke(Method.java:564)
[ERROR] at scala_maven_executions.MainHelper.runMain(MainHelper.java:164)
[ERROR] at scala_maven_executions.MainWithArgsInFile.main(MainWithArgsInFile.java:26)
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 8.256 s
[INFO] Finished at: 2019-04-17T08:46:16+02:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal net.alchim31.maven:scala-maven-plugin:3.3.1:compile (default-cli) on project util: wrap: org.apache.commons.exec.ExecuteException: Process exited with an error: 1 (Exit value: 1)
I also can run mvn compile which succeeds but produces an empty jar:
[INFO] Building util 0.0.1-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) # util ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory /Users/markus.geilehner/Documents/Syniverse/util/util/src/main/resources
[INFO]
[INFO] --- maven-compiler-plugin:3.7.0:compile (default-compile) # util ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 6 source files to /Users/markus.geilehner/Documents/Syniverse/util/util/target/classes
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.334 s
[INFO] Finished at: 2019-04-17T09:03:55+02:00
[INFO] ------------------------------------------------------------------------
Project File Structure
-util
--src
---main
----scala
-----com.company.util
------Scala Classes and packages
pom.xml
Here some parts of the pom.xml. I use the net.alchim Scala-maven plugin.
The build process is configured to use the scala directory.
<build>
<sourceDirectory>src/main/scala</sourceDirectory>
<testSourceDirectory>src/test/scala</testSourceDirectory>
<plugins>
<plugin>
<groupId>net.alchim31.maven</groupId>
<artifactId>scala-maven-plugin</artifactId>
<version>3.3.1</version>
</plugin>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>2.4</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-site-plugin</artifactId>
<version>3.0</version>
<configuration>
<reportPlugins>
<plugin>
<artifactId>maven-project-info-reports-plugin</artifactId>
<version>2.2</version>
</plugin>
<plugin>
<groupId>net.alchim31.maven</groupId>
<artifactId>scala-maven-plugin</artifactId>
<version>3.3.1</version>
<configuration>
<jvmArgs>
<jvmArg>-Xms64m</jvmArg>
<jvmArg>-Xmx1024m</jvmArg>
</jvmArgs>
</configuration>
</plugin>
</reportPlugins>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>${maven-compiler-plugin.version}</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>

Answer 1

Solution
I had the same error when working with a scala project combined with maven.
Issue-1
One Issue can be that you use the wrong Java-Version (9/10) try to change it to Java 8 (1.8) in IntelliJ (File => Project-Structure).
Issue-2
In your pom add the following execution beneath the maven-scala plugin.
<executions>
<execution>
<id>compile</id>
<goals>
<goal>compile</goal>
</goals>
<phase>compile</phase>
</execution>
<execution>
<id>test-compile</id>
<goals>
<goal>testCompile</goal>
</goals>
<phase>test-compile</phase>
</execution>
<execution>
<phase>process-resources</phase>
<goals>
<goal>compile</goal>
</goals>
</execution>
</executions>
Do a clean install an try again.