Question

I am using sbt for a simple, small GUI projects that load icons from src/main/scala/resources. At first, everything works fine and I can compile. package, and run. The generated jar and class files all have the resource folder in it. Then I do the clean command. I re-run the compile and package, and suddently the application crashes. I check the generated jars and classes, and found out that the resources folder are not copied this time.

Running the application now gives me the NullPointerException pointing to the line where I load the resource (icon).

I didn’t change the sbt build files or anything in the project. Just run clean and re-run compile and package. I don’t know where to start looking for the problem. Where should I start looking? What am I doing wrong?

EDIT (the minimal example)

The project is a standard Scala template from typesafe’s g8 (https://github.com/typesafehub/scala-sbt.g8). Here’s my Build.Scala:

import sbt._
import sbt.Keys._

object ObdscanScalaBuild extends Build {
  val scalaVer = "2.9.2"

  lazy val obdscanScala = Project(
    id = "obdscan-scala",
    base = file("."),
    settings = Project.defaultSettings ++ Seq(
      name := "project name",
      organization := "thesis.bert",
      version := "0.1-SNAPSHOT",
      scalaVersion := scalaVer,
      // add other settings here

      // resolvers

      // dependencies
      libraryDependencies ++= Seq (
        "org.scala-lang" % "scala-swing" % scalaVer,
        "org.rxtx" % "rxtx" % "2.1.7"
      )
    )
  )
}

It builds the code fine previously. Here’s the project code directory structure:

It works fine and output this directory inside the jar at first:

And suddently, when I do a clean and compile command via the sbt console, it didn’t copy the resource directory in the jar or in the class directory (inside target) anymore. I can’t do anything to get the resource directory copied to target now, except by restoring previous version and compile it one more time. I restore the previous version via Windows’ history backup.

Is it clear enough? Anything I need to add?

EDIT:

After moving the files to src/main/resources, the compiled files now contains the resources. But now, I can’t run it in eclipse. Here’s my code:

object ControlPanelContent {
  val IconPath = "/icons/"
  val DefaultIcon = getClass.getResource(getIconPath("icon"))

  def getImage(name: String) = {
    getClass.getResource(getIconPath(name))
  }

  def getIconPath(name: String) = {
    IconPath + name + ".png"
  }
}

case class ControlPanelContent(title: String, iconName: String) extends FlowPanel {
  name = title
  val icon: ImageIcon = createIcon(iconName, 64)

  val pageTitle = new Label(title)

  protected def createIcon(name: String, size: Int): ImageIcon = {
    val path: Option[URL] = Option(ControlPanelContent.getImage(name))

    val img: java.awt.Image = path match {
      case Some(exists) => new ImageIcon(exists).getImage
      case _            => new ImageIcon(ControlPanelContent.DefaultIcon).getImage
    }
    val resizedImg = img.getScaledInstance(size, size, Image.SCALE_SMOOTH)
    new ImageIcon(resizedImg)
  }
}

The TLDR version is this, I guess:

getClass.getResource("/icons/icon.png")

which works if I call from sbt console command. Here’s the result when I call the code from sbt console:

scala> getClass.getResource("/icons/icon.png")
res0: java.net.URL = file:/project/path/target/scala-2.9.2/classes/icons/icon.png

which when runned gives the following exception:

Caused by: java.lang.NullPointerException
    at javax.swing.ImageIcon.<init>(Unknown Source)
    at thesis.bert.gui.ControlPanelContent.createIcon(ControlPanel.scala:54)
    at thesis.bert.gui.ControlPanelContent.<init>(ControlPanel.scala:33)
    at thesis.bert.gui.controls.DTC$.<init>(Diagnostics.scala:283)
    at thesis.bert.gui.controls.DTC$.<clinit>(Diagnostics.scala)
    ... 60 more

EDIT 2: It works now. I just deleted the project from eclipse, re-run sbt eclipse and it magically works. Not sure why (maybe caching?).

Answer 1

The SBT convention for resources is to put them in src/main/resources/, not src/main/scala/resources/. Try moving your resources folder up one level. Its content should then be included, meaning that you will get icons and indicator folders inside the generated jar file (directly at the root level, not inside a resources folder).

If you put the resources in scala, I think it copies only the files that are compiled (i.e. .class files resulting from scala compilation).

If it doesn’t solve your problem, can you post the lines of code you use to load the resource?