SBT：如何Dockerize一个胖罐子？(SBT: How to Dockerize a fat jar?)

 回答我自己的问题，以下工作： 
 
enablePlugins(JavaAppPackaging, DockerPlugin)

assemblyMergeStrategy in assembly := {
  case x => {
    val oldStrategy = (assemblyMergeStrategy in assembly).value
    val strategy = oldStrategy(x)
    if (strategy == MergeStrategy.deduplicate)
      MergeStrategy.first
    else strategy
  }
}

// Remove all jar mappings in universal and append the fat jar
mappings in Universal := {
  val universalMappings = (mappings in Universal).value
  val fatJar = (assembly in Compile).value
  val filtered = universalMappings.filter {
    case (file, name) => !name.endsWith(".jar")
  }
  filtered :+ (fatJar -> ("lib/" + fatJar.getName))
}

dockerRepository := Some("username")

import com.typesafe.sbt.packager.docker.{Cmd, ExecCmd}
dockerCommands := Seq(
  Cmd("FROM", "username/spark:2.1.0"),
  Cmd("WORKDIR", "/"),
  Cmd("COPY", "opt/docker/lib/*.jar", "/app.jar"),
  ExecCmd("ENTRYPOINT", "/opt/spark/bin/spark-submit", "/app.jar")
)
 
 我完全覆盖了docker命令，因为默认添加了几个我不需要的脚本，因为我也覆盖了入口点。 此外，默认的workdir是/opt/docker ，这不是我想要放入胖罐的地方。 请注意，默认命令由sbt控制台中的show dockerCommands 。 

Answering my own questions, the following works:
 
enablePlugins(JavaAppPackaging, DockerPlugin)

assemblyMergeStrategy in assembly := {
  case x => {
    val oldStrategy = (assemblyMergeStrategy in assembly).value
    val strategy = oldStrategy(x)
    if (strategy == MergeStrategy.deduplicate)
      MergeStrategy.first
    else strategy
  }
}

// Remove all jar mappings in universal and append the fat jar
mappings in Universal := {
  val universalMappings = (mappings in Universal).value
  val fatJar = (assembly in Compile).value
  val filtered = universalMappings.filter {
    case (file, name) => !name.endsWith(".jar")
  }
  filtered :+ (fatJar -> ("lib/" + fatJar.getName))
}

dockerRepository := Some("username")

import com.typesafe.sbt.packager.docker.{Cmd, ExecCmd}
dockerCommands := Seq(
  Cmd("FROM", "username/spark:2.1.0"),
  Cmd("WORKDIR", "/"),
  Cmd("COPY", "opt/docker/lib/*.jar", "/app.jar"),
  ExecCmd("ENTRYPOINT", "/opt/spark/bin/spark-submit", "/app.jar")
)
 
I completely overwrite the docker commands because the defaults add couple of scripts that I don't need because I overwrite the entrypoint as well. Also, the default workdir is /opt/docker which is not where I want to put the fat jar. Note that the default commands are shown by show dockerCommands in sbt console.