objectrunner.scala

来自「JAVA 语言的函数式编程扩展」· SCALA 代码 · 共 79 行

/* NSC -- new Scala compiler
 * Copyright 2005-2007 LAMP/EPFL
 * @author  Lex Spoon
 */

// $Id: ObjectRunner.scala 13593 2007-12-19 13:21:09Z odersky $

package scala.tools.nsc

import java.lang.{Class, ClassNotFoundException, NoSuchMethodException}
import java.lang.reflect.{Method, Modifier}
import java.net.{URL, URLClassLoader}

/** An object that runs another object specified by name.
 *
 *  @author  Lex Spoon
 *  @version 1.1, 2007/7/13
 */
object ObjectRunner {
  /** Create a class loader for the specified class path */
  private def makeClassLoader(classpath: List[URL]) =
    new URLClassLoader(classpath.toArray, null)

  /** Look up a class with a given class path. */
  private def findClass(loader: ClassLoader, objectName: String)
  : Option[Class[T] forSome { type T }] = 
  {
    try {
      Some(Class.forName(objectName, true, loader))
    } catch {
      case e: SecurityException =>
        Console.println(e.getMessage)
        None
      case _: ClassNotFoundException =>
        None
    }
  }
  
  /** Check whether a class with the specified name
   *  exists on the specified class path. */
  def classExists(classpath: List[URL], objectName: String): Boolean =
    !findClass(makeClassLoader(classpath), objectName).isEmpty

  /** Set the Java context class loader while executing an action */
  def withContextClassLoader[T](loader: ClassLoader)(action: =>T): T = {
    val oldLoader = Thread.currentThread.getContextClassLoader
    try {
      Thread.currentThread.setContextClassLoader(loader)
      action
    } finally {
      Thread.currentThread.setContextClassLoader(oldLoader)
    }
  }

  
  /** Run a given object, specified by name, using a
   *  specified classpath and argument list.
   *
   *  @throws ClassNotFoundException   
   *  @throws NoSuchMethodError         
   *  @throws InvocationTargetException 
   */
  def run(classpath: List[URL], objectName: String, arguments: Seq[String]) {
    val loader = makeClassLoader(classpath)
    val clsToRun = findClass(loader, objectName) match {
      case Some(cls) => cls
      case None => throw new ClassNotFoundException(objectName)
    }

    val method = clsToRun.getMethod("main", List(classOf[Array[String]]).toArray)
    if ((method.getModifiers & Modifier.STATIC) == 0)
      throw new NoSuchMethodException(objectName + ".main is not static")

    withContextClassLoader(loader) {
      method.invoke(null, List(arguments.toArray).toArray)
    }
  }
}