Pattern matching against URL with question mark in Scala - scala

Question

I am trying to extract few values from the URL consisting of question mark.
However, the below code doesn't work. Would you please help me in figuring out what went wrong?
val LibraryPattern = ".*/library/([A-Za-z0-9\\-]+)?book=([A-Za-z0-9\\-]+)".r
val url = "https://bookscollection.com/library/mylib?book=abc"
Try(new URL(url)) match {
case Success(url) =>
println("my url:"+url)
url.getPath match {
case LibraryPattern(libId, bookId) =>
println(libId)
println(bookId)
case _ =>
}
}

Answer 1

As few answer already pointed how to fix code example, I want to suggest another solution. Parsing URL with regex may be inefficient in terms of future readability, type safety and flexability of your codebase.
I want to suggest using scala-uri library or something similar.
With this library one can do url parsing as simple as:
import io.lemonlabs.uri.Url
val url = Url.parse("https://bookscollection.com/library/mylib?book=abc")
val lastPathPart = url.path.parts.last
// println(lastPathPart)
// res: String = "mylib"
val bookParam: Option[String] = url.query.param("book")
// println(bookParam)
// res: Option[String] = Some("abc")

Answer 2

The URL object has already parsed the URL for you. getPath returns everything before the ?, use getQuery to obtain the part after the ?:
val LibraryPattern = ".*/library/([A-Za-z0-9\\-]+)".r
val BookPattern = "book=([A-Za-z0-9\\-]+)".r
val url = "https://bookscollection.com/library/mylib?book=abc"
Try(new URL(url)) match {
case Success(url) =>
url.getPath match {
case LibraryPattern(libId) =>
url.getQuery match {
case BookPattern(bookId) =>
println(libId)
println(bookId)
}
}
}

Answer 3

? is a special character in Regex (it essentially makes the previous character/group optional). You'll need to escape it.
EDIT: url.getPath only returns /library/mylib, so you shouldn't use this if you want your Regex to match.
val LibraryPattern = ".*/library/([A-Za-z0-9\\-]+)\\?book=([A-Za-z0-9\\-]+)".r
val url = "https://bookscollection.com/library/mylib?book=abc"
Try(new URL(url)) match {
case Success(url) =>
println("my url:"+url)
url.toString match {
case LibraryPattern(libId, bookId) =>
println(libId)
println(bookId)
case _ =>
}
}