Supports tracer bullet dynamic logging

TracerBulletController.scala

package controllers

import javax.inject._
import play.api.mvc._

@Singleton
class TracerBulletController @Inject() extends Controller {
  private val logger = org.slf4j.LoggerFactory.getLogger("application")

  /*
  <turboFilter class="ch.qos.logback.classic.turbo.MarkerFilter">
    <Name>TRACER_FILTER</Name>
    <Marker>TRACER</Marker>
    <OnMatch>ACCEPT</OnMatch>
  </turboFilter>
   */
  private val tracerMarker = org.slf4j.MarkerFactory.getMarker("TRACER")

  def generateMarker(implicit request: RequestHeader): org.slf4j.Marker = {
    // You can return null here, but I prefer to at least have a base do-nothing marker...
    val marker = org.slf4j.MarkerFactory.getDetachedMarker("dynamic")
    request match {
      case r if r.getQueryString("trace").nonEmpty  =>
        marker.add(tracerMarker)
        marker
      case other =>
        marker
    }
  }

  def index = Action { implicit request =>
    val marker = generateMarker
    if (logger.isTraceEnabled(marker)) {
      logger.trace(marker, "Hello world!")
    }
    Ok("hello world")
  }
}