Problem creating an executable jar from scala file.

Question

I'm tryign to export my project as a jar with IntelliJ 9.0. My project compiles and runs with no problem in Intellij, but when I write it to a .jar and open it, it will show an error.

My Main class is something like:

package Main

//Imports

object Main{
  def main(args: Array[String]) {
    println("Main: Hello, world!")
    //do stuff
}

Now, in the artifacts window I created a .jar with the following:

1. Main Clas: Main.Main
2. Class Path: lib/javacsv lib/scala-compiler.jar lib/scala-library.jar lib/scalatest-1.0-test.jar lib/scalatest-1.0.jar lib/tools.jar lib/jtds-1.2.2.jar lib/flex-messaging-common.jar lib/flex-messaging-core.jar lib/spring.jar lib/mysql-connector-java-5.1.7-bin.jar lib/ojdbc14.jar lib/commons-logging.jar lib/postgresql-8.4-701.jdbc3.jar lib/log4j-1.2.15.jar lib/poi-3.6-20091214.jar lib/poi-ooxml-3.6-20091214.jar lib/dom4j-1.6.1.jar lib/poi-ooxml-schemas-3.6-20091214.jar lib/geronimo-stax-api_1.0_spec-1.0.jar lib/xmlbeans-2.3.0.jar lib/rt.jar lib/ifxjdbc.jar lib/db2jcc4.jar

I have double checked that all those classes are on the project and are the onnly classes on it. Notice that it inlcudes lib/scala-compiler.jar and lib/scala-library.jar.

Build the project: java -jar myScalaApp.jar and I get:

Exception in thread "main" java.lang.NoClassDefFoundError: scala/ScalaObject
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:675)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
    at java.net.URLClassLoader.access$000(URLClassLoader.java:56)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:316)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:288)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
    at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:374)
    at Main.Main.main(Main.scala)
Caused by: java.lang.ClassNotFoundException: scala.ScalaObject
    at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:316)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:288)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
    at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:374)
    ... 13 more

I understand that it's not finding the scala classes but I made sure they are there. What else can be the problem and how could I fix it?

Answer 1

I'd say one of two things has gone wrong:

• scala-library.jar is not in your jar; or
• the class path at runtime doesn't include scala-library.jar.

I don't know how IntelliJ builds your jar: Does it unpack all your library jars and mung them together with your code into one big jar, or does it add the library jars as-is to your big jar and manipulate the classpath to get at the jars-within-jar?

The first point is easy enough to check: Either use jar -tvf yourJar.jar to list out the contents of your jar, or use an archive viewer to look into it graphically. Note that a .jar is basically a .zip, so you can rename the extension and then use a tool that can look into .zip files.

Just had an idea about the second part: Can you build a simple Java main class that prints out System.getProperty("java.class.path") ? A Java class should be able to run in that jar even if a Scala class isn't.