scala正则表达式实战

案例一

说明：源码来自spark ConfigReader类

private object ConfigReader {

  private val REF_RE = "\\$\\{(?:(\\w+?):)?(\\S+?)\\}".r

}
private def substitute(input: String, usedRefs: Set[String]): String = {
    if (input != null) {
      ConfigReader.REF_RE.replaceAllIn(input, { m =>
        val prefix = m.group(1)
        val name = m.group(2)
        val ref = if (prefix == null) name else s"$prefix:$name"
        require(!usedRefs.contains(ref), s"Circular reference in $input: $ref")

        val replacement = bindings.get(prefix)
          .flatMap(getOrDefault(_, name))
          .map { v => substitute(v, usedRefs + ref) }
          .getOrElse(m.matched)
        Regex.quoteReplacement(replacement)
      })
    } else {
      input
    }
  }