Play Framework 2.3 no resources after migration - resources

Question

I have a play framework 2.1 application. This app worked. Then I migrated to 2.2, tested it and it worked. Now I am migrating to 2.3 and I got an error like:
[debug] application - Unforseen error for favicon.svg at /public
java.lang.RuntimeException: no resource
at controllers.Assets$$anonfun$controllers$Assets$$assetInfoFromResource$1$$anonfun$13.apply(Assets.scala:237) ~[na:na]
at controllers.Assets$$anonfun$controllers$Assets$$assetInfoFromResource$1$$anonfun$13.apply(Assets.scala:237) ~[na:na]
at scala.Option.getOrElse(Option.scala:120) [na:na]
at controllers.Assets$$anonfun$controllers$Assets$$assetInfoFromResource$1.apply(Assets.scala:237) ~[na:na]
at controllers.Assets$$anonfun$controllers$Assets$$assetInfoFromResource$1.apply(Assets.scala:236) ~[na:na]
There is a /public folder, but all resources are resulting in above error. The app serves such resources as 404 Not Found.
Any help would be great. Some cleaning procecese, cached files I can delete, redownload dependencies or maybe I have a wrong configuration.
Here are some config files I have for better understanding:
build.sbt:
import com.typesafe.sbt.less.Import.LessKeys import play.PlayJava
name := """blabla-de"""
version := "1.0-SNAPSHOT"
lazy val root = (project in file(".")).enablePlugins(PlayJava)
scalaVersion := "2.11.1"
libraryDependencies ++= Seq( filters, cache, javaCore, javaWs, javaJdbc, javaEbean, "org.webjars" % "bootstrap" % "3.0.0", "org.webjars" % "rjs" % "2.1.11-1-trireme" % "test", "org.webjars" % "squirejs" % "0.1.0" % "test", "junit" % "junit" % "4.11" % "test" )
testOptions += Tests.Argument(TestFrameworks.JUnit, "-v")
LessKeys.compress in Assets := true
includeFilter in (Assets, LessKeys.less) := "*.less"
excludeFilter in (Assets, LessKeys.less) := "_*.less"
pipelineStages := Seq(rjs, digest, gzip)
conf/routes:
# Home page
GET / controllers.Index.index()
GET /about controllers.About.index()
## Contact Page
GET /contact controllers.Contact.index()
POST /contact controllers.Contact.newContact()
## Gallery List
GET /portfolio controllers.Portfolio.index()
## Text(HTML) Page
GET /impressum controllers.Impressum.index()
#GET /legal
GET /privacy controllers.Privacy.index()
# Map static resources from the /public folder to the / URL path
GET /*file controllers.Assets.at(path="/public", file)
project/build.properties:
sbt.version=0.13.5
project/plugins.sbt:
// Comment to get more information during initialization
logLevel := Level.Warn
// The Typesafe repository
resolvers += "Typesafe repository" at "http://repo.typesafe.com/typesafe/releases/"
// The Play plugin
addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.3.1")
// web plugins
addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.3.1")
addSbtPlugin("com.typesafe.sbt" % "sbt-less" % "1.0.0")
addSbtPlugin("com.typesafe.sbt" % "sbt-coffeescript" % "1.0.0")
addSbtPlugin("com.typesafe.sbt" % "sbt-rjs" % "1.0.1")
addSbtPlugin("com.typesafe.sbt" % "sbt-digest" % "1.0.0")
addSbtPlugin("com.typesafe.sbt" % "sbt-gzip" % "1.0.0")
addSbtPlugin("com.typesafe.sbt" % "sbt-mocha" % "1.0.0")
Thank You in Advance.

Answer 1

The key is in the migration guide: https://www.playframework.com/documentation/2.4.x/Migration23
The largest new feature for Play 2.3 is the introduction of sbt-web.
In summary sbt-web allows Html, CSS and JavaScript functionality to be
factored out of Play’s core into a family of pure sbt plugins.
Unavailability of public resources must be caused by improper configuration of sbt-web.
What I can see immediately is that you forgot to enable SbtWeb plugins. Here is another quote from the migration guide:
declaring addSbtPlugin may not be sufficient for plugins that now
utilize to the auto plugin functionality.
So you need to fix the following line in your build.sbt:
lazy val root = (project in file(".")).enablePlugins(PlayJava, SbtWeb)