在 try finally 的finally块中访问try中定义变量的一种变通方式。

gistfile1.scala

package demo

import java.io.{IOException, FileOutputStream}

object TryCatchFinally {
  def trying[T, R](
                    in: => T,
                    func: T => R,
                    catchFunc: Throwable => R,
                    finallyFunc: T => Unit): R = {
    var value: Option[T] = null
    try {
      value = Option(in)
      func(value.get)
    } catch {
      case e: Throwable =>
        catchFunc(e)
    } finally {
      value.foreach(finallyFunc)
    }
  }

  def tryoption[R](func: => R): Option[R] =
    try {
      val ret = func
      Option(ret)
    } catch {
      case _: Throwable =>
        None
    }

  def tryeither[R](func: => R): Either[Throwable, R] =
    try {
      val ret = func
      Right(ret)
    } catch {
      case e: Throwable =>
        Left(e)
    }

  def tryfinally[T, R](in: => T, func: T => R, finallyFunc: T => Unit): R = {
    var value: Option[T] = None
    try {
      value = Option(in)
      func(value.get)
    } finally {
      value.foreach(finallyFunc)
    }
  }

  // 注意有多个变量时finally的不同
  def tryfinally[A, B, R](in1: => A, in2: => B, func: (A, B) => R, finallyFunc: (Option[A], Option[B]) => Unit): R = {
    var a: Option[A] = None
    var b: Option[B] = None
    try {
      a =  Option(in1)
      b =  Option(in2)
      func(a.get, b.get)
    } finally {
      finallyFunc(a, b)
    }
  }

  def main(args: Array[String]) {
    val ret =
      trying[FileOutputStream, Int](
        new FileOutputStream("/tmp/ttt.txt"),
        out => {
          val msg = "中华人民共和国".getBytes("UTF-8")
          out.write(msg)
          msg.length
        },
        _ => -1,
        _.close()
      )

    println(s"已向文件文件写入：${ret} 字节。")

    // 将抛出异常
    tryfinally[FileOutputStream, Int](
      new FileOutputStream("/tmp/ttt.txt"),
      out => {
        val msg = "中华人民共和国".getBytes("UTF-8")
        out.write(msg)
        throw new RuntimeException()
        msg.length
      },
      t => {
        println("已关闭文件资源")
        t.close()
      })

  }

}