When doing something in an SBT console which requires the loading of Case Class instances via fig or jerkson ClassNotFoundExceptions will be generated because the console runs in a different ClassLoader than the one responsible for loading other classpath classes. As a result the ClassLoader reflection used to make this bit of case class magic doesn’t work unless the code is executed within a Thread which has had it’s ClassLoader set to the original. This is where inClassLoader comes in. Code executed within this beautiful function will produce a result rather than a ClassNotFoundException.

For example in Persnicketly:

val articles = inClassLoader(classOf[com.persnicketly.persistence.Connection$]) {
  ScoredArticleDao.select(from = 60, count = 100)
}

Will successfully load MongoDB configuration from config.json, access the db and retrieve articles.

Source of inClassLoader:

def inClassLoader[T](cls: Class[_])(f: => T): T = {
  val prev = Thread.currentThread.getContextClassLoader
  try {
    Thread.currentThread.setContextClassLoader(
       cls.getClassLoader
    )
    f
  } finally {
    Thread.currentThread.setContextClassLoader(prev)
  }
}

Code provided by softprops in issue #38 of jerkson.