sbt 运行 IMain 并且 play 出错答案

【问题标题】：sbt runs IMain and play makes errorssbt 运行 IMain 并且 play 出错
【发布时间】：2014-05-29 11:23:56
【问题描述】：

我已经构建了一个小对象，它可以即时解释 scala 代码并从中获取值。

object Interpreter {
  import scala.tools.nsc._
  import scala.tools.nsc.interpreter._

  class Dummy

  val settings = new Settings
  settings.usejavacp.value = false
  settings.embeddedDefaults[Dummy]  // to make imain useable with sbt.

  val imain = new IMain(settings)

  def run(code: String, returnId: String) = {
    this.imain.beQuietDuring{
      this.imain.interpret(code)
    }
    val ret = this.imain.valueOfTerm(returnId)
    this.imain.reset()
    ret
  }
}

object Main {
  def main(args: Array[String]) {
    println(Interpreter.run("val x = 1", "x"))
  }
}

在纯sbt 环境中或由scala 解释器调用此代码可以正常工作！但是如果我在一个简单的play（2.2.2 版）应用程序中运行它，它会在val ret = this.imain.valueOfTerm(returnId) 处获得一个空指针。

play 也使用 modified sbt，因此它应该可以工作。 play 做了什么使这段代码不再起作用？任何想法如何让此代码在play 中工作？

注意

那是用过的build.sbt：

name := "Test"

version := "1.0"

scalaVersion := "2.10.3"

libraryDependencies += "org.scala-lang" % "scala-compiler" % scalaVersion.value

或者我尝试了这个实现，但它也没有解决问题：

object Interpreter2 {
  import scala.tools.nsc._
  import scala.tools.nsc.interpreter._
  import play.api._
  import play.api.Play.current 

  val settings: Settings = {
    lazy val urls = java.lang.Thread.currentThread.getContextClassLoader match {
      case cl: java.net.URLClassLoader => cl.getURLs.toList
      case _ => sys.error("classloader is not a URLClassLoader")
    }

    lazy val classpath = urls map {_.toString}

    val tmp = new Settings()
    tmp.bootclasspath.value = classpath.distinct mkString java.io.File.pathSeparator
    tmp
  }

  val imain = new IMain(settings)

  def run(code: String, returnId: String) = {
    this.imain.beQuietDuring {
      this.imain.interpret(code)
    }
    val ret = this.imain.valueOfTerm(returnId)
    this.imain.reset()
    ret
  }
}

我发现用于实现第二个实现的有用链接：

【问题讨论】：

标签： scala playframework-2.2

【解决方案1】：

我自己在这个问题上花了几个小时后，我想出了一个解决方案。它在 SBT 内部和外部都有效。它还有望在各种托管环境（如 OSGi）中工作：

private def getClasspathUrls(classLoader: ClassLoader, acc: List[URL]): List[URL] = {
    classLoader match {
      case null                        => acc
      case cl: java.net.URLClassLoader => getClasspathUrls(classLoader.getParent, acc ++ cl.getURLs.toList)
      case c                           => LOGGER.error("classloader is not a URLClassLoader and will be skipped. ClassLoader type that was skipped is " + c.getClass)
                                          getClasspathUrls(classLoader.getParent, acc)
    }
}
val classpathUrls = getClasspathUrls(this.getClass.getClassLoader, List())
val classpathElements = classpathUrls map {url => url.toURI.getPath}
val classpath = classpathElements mkString java.io.File.pathSeparator
val settings = new Settings
settings.bootclasspath.value = classpath
val imain = new IMain(settings)
// use imain to interpret code. It should be able to access all your application classes as well as dependent libraries.

【讨论】：

【解决方案2】：

这是因为play 使用了sbt 的“fork in run”功能。这个特性会启动一个新的JVM，这会导致出现这个故障：

[info] Failed to initialize compiler: object scala.runtime in compiler mirror not found.
[info] ** Note that as of 2.8 scala does not assume use of the java classpath.
[info] ** For the old behavior pass -usejavacp to scala, or if using a Settings
[info] ** object programatically, settings.usejavacp.value = true.

见：http://www.scala-sbt.org/release/docs/Detailed-Topics/Forking

【讨论】：