使用 Scala 组合器解析创建对象实例

Question

我有这个解析器：

import scala.util.parsing.combinator.JavaTokenParsers

class RequestMappingParser extends JavaTokenParsers {
  def requestMapping: Parser[Any] = "@RequestMapping(" ~ commaDelimitedSeq ~ ")"
  def commaDelimitedSeq: Parser[Any] = repsep(keyValue, ",")
  def keyValue: Parser[Any] = key ~ "=" ~ value
  def key: Parser[Any] = "value" | "method"
  def value: Parser[Any] = """[^)]*""".r
}

我有这个简单的 class:

class MethodRequestMapping(val value: String, val method: String)

我的解析器可以解析这个字符串：

"@RequestMapping(value = \"/ex/foos\", method = RequestMethod.GET)"

和 return 是 Parser[Any] 的结果。我希望 return 是 Parser[MethodRequestMapping].

的结果

我该怎么做？我知道我必须做这样的事情：

def requestMapping: Parser[MethodRequestMapping] = "@RequestMapping(" ~ commaDelimitedSeq ~ ")" ^^ {
  // Some sort of pattern matching and creation of MethodRequestMapping
  // ???
}

但 ????还是换一种完全不同的方式更好？

Answer 1

首先，您使用的一半组合被创建为 Parser[String]，并且是您的类型注释将它们向上转换为 Parser[Any]（由于协方差，这是允许的，但在这种情况）。

所以你实际上有这样的东西：

class RequestMappingParser extends JavaTokenParsers {
  def requestMapping: Parser[String ~ List[String ~ String ~ String] ~ String] = "@RequestMapping(" ~ commaDelimitedSeq ~ ")"
  def commaDelimitedSeq: Parser[List[String ~ String ~ String]] = repsep(keyValue, ",")
  def keyValue: Parser[String ~ String ~ String] = key ~ "=" ~ value
  def key: Parser[String] = "value" | "method"
  def value: Parser[String] = """[^)]*""".r
}

然后我们可以使用 map 或 ^^ 来调整类型 - 之前它很困难，因为我们在那里有 Any，但如果我们不摆脱类型，我们将能够轻松进行模式匹配

class RequestMappingParser extends JavaTokenParsers {
  // result of this parser will be ethier "value" or "method"
  def key: Parser[String] = "value" | "method"
  def value: Parser[String] = """[^),]*""".r // you had an error here, you were missing "," to separate items
  // here we'll map String ~ String ~ String to tuple - we'll drop unused "=" in the process
  def keyValue: Parser[(String, String)] = (key ~ "=" ~ value).map {
    case k ~ _ ~ v => k -> v
  }
  // repsep wil return List[(String, String)], which we'll map to Map
  def commaDelimitedSeq: Parser[Map[String, String]] = repsep(keyValue, ",").map(_.toMap)
  // this would give us String ~ Map[String, String] ~ String, but we don't need
  // these String constants. Also we can map things into out final result
  def requestMapping: Parser[MethodRequestMapping] = ("@RequestMapping(" ~ commaDelimitedSeq ~ ")").map {
    case _ ~ map ~ _ =>
      new MethodRequestMapping(value = map("value"), method = map("method"))
  }
}

val parser = new RequestMappingParser()
val parsed = "@RequestMapping(value = \"/ex/foos\", method = RequestMethod.GET)"
val result = parser.parse(parser.requestMapping, parsed).get
// result.value == "\"/ex/foos\""
// result.method == "RequestMethod.GET"

就是说 - 不鼓励使用此解析器组合库，主要是因为它很慢。对于生产，建议使用类似 FastParse 的东西，它具有更快的实施速度和更多的功能。

使用 Scala 组合器解析创建对象实例

Creating an instance of an object using Scala combinator parsing

parsing

scala

parser-combinators