Failed to build Scala program with gradle and java library dependencies

Question

I have somewhat simple proplem (too hard for me though):

I am trying to build a simple Scala test program, which has Java library dependencies, using gradle. My test program is following

src/main/scala/test.scala

import org.ejml.simple.SimpleMatrix

object test {
  def main(args: Array[String]): Unit = {
    val M = new SimpleMatrix(2,2)
    println("Created matrix succesfully")
  }  
}

My build.gradle looks like this:

apply plugin: 'scala'

repositories {
    mavenCentral()  
}

dependencies {
    compile group: 'org.ejml', name: 'all', version: '0.30'
    compile 'org.scala-lang:scala-library:2.12.0'
}

When I build my test program with

./gradlew clean assemble

I get the proper folder structure (build/classes/main/test.class).

If I now try to run test.class with

scala test

I get the following error:

java.lang.ClassNotFoundException: org.ejml.simple.SimpleMatrix
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at test$.main(test.scala:7)
    at test.main(test.scala)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at scala.reflect.internal.util.ScalaClassLoader.$anonfun$run$2(ScalaClassLoader.scala:98)
    at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.asContext(ScalaClassLoader.scala:32)
    at scala.reflect.internal.util.ScalaClassLoader.run(ScalaClassLoader.scala:98)
    at scala.reflect.internal.util.ScalaClassLoader.run$(ScalaClassLoader.scala:90)
    at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:129)
    at scala.tools.nsc.CommonRunner.run(ObjectRunner.scala:22)
    at scala.tools.nsc.CommonRunner.run$(ObjectRunner.scala:21)
    at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:39)
    at scala.tools.nsc.CommonRunner.runAndCatch(ObjectRunner.scala:29)
    at scala.tools.nsc.CommonRunner.runAndCatch$(ObjectRunner.scala:28)
    at scala.tools.nsc.ObjectRunner$.runAndCatch(ObjectRunner.scala:39)
    at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:65)
    at scala.tools.nsc.MainGenericRunner.run$1(MainGenericRunner.scala:92)
    at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:103)
    at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:108)
    at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

So it seems that the EJML is not linked properly. Looks like I am overlooking something but I can't think of what. I confirmed that EJML library is downloaded

$ ls ~/.gradle/caches/modules-2/files-2.1/org.ejml/
 all        core        dense64     denseC64    equation    simple

This program also builds fine if I use Eclipse and add the .jars manually to the project

I've built java project with gradle successfully in the past using this same process (its been a few years though). Any help is appreciated.

PS. just to clarify, I am trying to build using command line. Eclipse (and other IDEs) work fine if I add the JARs manually

PPS. the program runs until line "val M = ..." (tested)

score 1 · Accepted Answer · answered Mar 25 '17 at 12:06

In this case I like to use the Gradle Application Plugin to

run your Scala Code
build a Distribution Tar (Linux) or Zip (Windows).

I see you already use the Gradle Wrapper.

Extend your build.gradle with:

apply plugin: 'scala'
apply plugin: 'application' // added

repositories {
    mavenCentral()  
}

dependencies {
    compile group: 'org.ejml', name: 'all', version: '0.30'
    compile 'org.scala-lang:scala-library:2.12.0'
}

mainClassName = 'test' // added

Extend your test program src/main/scala/test.scala with more Output:

import org.ejml.simple.SimpleMatrix

object test {
    def main(args: Array[String]): Unit = {
        val m = new SimpleMatrix(2,2)
        println("Created matrix succesfully: " + m)
    }  
}

Then let gradle build and run your Scala test program with - instead use of scala test

./gradlew clean run

Now you get your Output without Error:

$ ./gradlew clean run
:clean
:compileJava NO-SOURCE
:compileScala
:processResources NO-SOURCE
:classes
:run
Created matrix succesfully: Type = dense real , numRows = 2 , numCols = 2
 0.000   0.000
 0.000   0.000

Additionally let gradle build a Distribution Tar (Linux) or Zip (Windows)

$ ./gradlew clean assemble
:compileJava NO-SOURCE
:compileScala UP-TO-DATE
:processResources NO-SOURCE
:classes UP-TO-DATE
:jar
:startScripts
:distTar
:distZip
:assemble

Have a look at build\distributions

a Tar File for Linux
a Zip File for Windows

In this Distributions Tar / Zip you will find this Structure:

+---bin
|       YourProjectDirName (start up script for UN*X)
|       YourProjectDirName.bat (startup script for Windows)
|
\---lib (alle needed Libs)
        all-0.30.jar
        core-0.30.jar
        dense64-0.30.jar
        denseC64-0.30.jar
        equation-0.30.jar
        scala-library-2.12.0.jar
        simple-0.30.jar
        SimpleMatrixScala.jar

Alternativ use

$ ./gradlew clean installDist
:compileJava NO-SOURCE
:compileScala UP-TO-DATE
:processResources NO-SOURCE
:classes UP-TO-DATE
:jar UP-TO-DATE
:startScripts UP-TO-DATE
:installDist

and have a look at build\install

you will find the distributions Structure Files

Failed to build Scala program with gradle and java library dependencies

1 Answers1