regex - 使用 Scala 模式匹配时工作正则表达式失败

Question

在以下代码中，使用 Java API 时匹配相同的模式，但使用 Scala 模式匹配时不匹配。

import java.util.regex.Pattern

object Main extends App {
  val text = "/oAuth.html?state=abcde&code=hfjksdhfrufhjjfkdjfkds"

  val statePatternString = """\/.*\?.*state=([^&\?]*)"""
  val statePattern = statePatternString.r
  val statePatternJ = Pattern.compile(statePatternString)

  val sj = statePatternJ.matcher(text)
  val sjMatch = if (sj.find()) sj.group(1) else ""
  println(s"Java match $sjMatch")

  val ss = statePattern.unapplySeq(text)
  println(s"Scala unapplySeq $ss")
  val sm = statePattern.findFirstIn(text)
  println(s"Scala findFirstIn $sm")

  text match {
    case statePattern(s) =>
      println(s"Scala matching $s")
    case _ =>
      println("Scala not matching")
  }

}

应用程序输出是:

Java match abcde

Scala unapplySeq None

Scala findFirstIn Some(/oAuth.html?state=abcde)

Scala not matching

使用提取器语法时 val statePattern(se) = text错误是 scala.MatchError .
是什么导致 Scala 正则表达式 unapplySeq 失败？

Answer 1

当你定义一个 Scala 模式时，它默认是 anchor 定的(=需要一个完整的字符串匹配)，而你的 Java sj.find()正在寻找字符串内任何地方的匹配项。添加 .unanchored Scala 正则表达式也允许部分匹配:

val statePattern = statePatternString.r.unanchored
                                       ^^^^^^^^^^^

见 IDEONE demo

一些 UnanchoredRegex reference :

def unanchored: UnanchoredRegex

Create a new Regex with the same pattern, but no requirement that the entire String matches in extractor patterns.

Normally, matching on date behaves as though the pattern were enclosed in anchors, ^pattern$.

The unanchored Regex behaves as though those anchors were removed.

Note that this method does not actually strip any matchers from the pattern.

替代解决方案 意味着添加 .* 在模式末尾，但请记住，默认情况下点不匹配换行符。如果解决方案应该是通用的，则 (?s)应在模式开头指定 DOTALL 修饰符，以确保匹配具有潜在换行符序列的整个字符串。