gistfile1.scala

def in(header:String) : Any = // existing method
  exchange.getIn.getHeader(header)

def in[T](header: String)(implicit manifest: Manifest[T]) : T = // new method that supports type
  exchange.getIn.getHeader(header, manifest.runtimeClass).asInstanceOf[T]

// existing code
val fileName = ex.in("CamelFileName") // fileName is any, which is normally casted

// passing a type, better
val fileName = ex.in[String]("CamelFileName")

// possible working solution, but I don't fully understand why/how it works

def in[T](header: String)(implicit e : T DefaultsTo Any, manifest: Manifest[T]) : T = 
  exchange.getIn.getHeader(header, manifest.runtimeClass).asInstanceOf[T]
  
sealed class DefaultsTo[A, B]
trait LowPriorityDefaultsTo {
   implicit def overrideDefault[A,B] = new DefaultsTo[A,B]
}
object DefaultsTo extends LowPriorityDefaultsTo {
   implicit def default[B] = new DefaultsTo[B, B]
}