FileController.scala

package controllers

import play.api._
import play.api.mvc._
import models.Files
import play.api.libs.json.Json
import scala.concurrent.Future
import play.api.libs.concurrent.Execution.Implicits._

object FileController extends SecuredController {

  def countChars = Action.async {
    Future {
      val chars = Files.countChars("public/files/chars.txt")
      Ok(Json.obj("chars" -> chars))
    }
  }

  def countCharsBlocking = Action {
    val chars = Files.countChars("public/files/chars.txt")
    Ok(Json.obj("chars" -> chars))
  }
}

Files.scala

package models

import scala.io.Source

object Files {

  def countChars(filePath: String): Long = {
    val source = Source.fromFile(filePath)

    var chars = 0L
    for (line <- source.getLines) {
      chars += line.toCharArray.size
    }

    source.close()

    chars
  }
}

routes

GET     /count                      controllers.FileController.countChars()
GET     /countBlocking              controllers.FileController.countCharsBlocking()