String pattern matching best practice

Following is the code that doesn't work but it describes what I want to do.

Could you please recommend the best approach to this problem?

def resolveDriver(url: String) = {
  url match {
    case url.startsWith("jdbc:mysql:") => "com.mysql.jdbc.Driver"
    case url.startsWith("jdbc:postgresql:") => "org.postgresql.Driver"
    case url.startsWith("jdbc:h2:") => "org.h2.Driver"
    case url.startsWith("jdbc:hsqldb:") => "org.hsql开发者_JS百科db.jdbcDriver"
    case _ => throw new IllegalArgumentException
  }
}

---

In terms of syntax, you can modify just a tiny bit you case statements:

case url if url.startsWith("jdbc:mysql:") => "com.mysql.jdbc.Driver"

This simply binds the value url to the pattern expression (which is also url) and adds a guard expression with a test. That should make the code compile.

To make it a little bit more scala-like, you can return an Option[String] (I removed a couple clause since it's just for illustration):

def resolveDriver(url: String) = url match {
  case u if u.startsWith("jdbc:mysql:") => Some("com.mysql.jdbc.Driver")
  case u if u.startsWith("jdbc:postgresql:") => Some("org.postgresql.Driver")
  case _ => None
}

That is unless you want to manage exceptions.

---

Here is an alternate way. Store all the mappings in a map and then use collectFirst method to find the match. Type signature of collectFirst is:

def TraversableOnce[A].collectFirst[B](pf: PartialFunction[A, B]): Option[B]

Usage:

scala> val urlMappings = Map("jdbc:mysql:" -> "com.mysql.jdbc.Driver", "jdbc:postgresql:" -> "org.postgresql.Driver")
urlMappings: scala.collection.immutable.Map[java.lang.String,java.lang.String] = Map(jdbc:mysql: -> com.mysql.jdbc.Drive
r, jdbc:postgresql: -> org.postgresql.Driver)

scala> val url = "jdbc:mysql:somestuff"
url: java.lang.String = jdbc:mysql:somestuff

scala> urlMappings collectFirst { case(k, v) if url startsWith k => v }
res1: Option[java.lang.String] = Some(com.mysql.jdbc.Driver)

---

Starting Scala 2.13, it's possible to pattern match a Strings by unapplying a string interpolator:

val s"jdbc:$dialect:$rest" = "jdbc:mysql:whatever"
// dialect: String = "mysql"
// rest: String = "whatever"

Then in our case, it's just a matter of mapping the extracted value (the sql dialect) to the appropriate driver using a Map:

val drivers = Map(
  "postgresql" -> "org.postgresql.Driver",
  "mysql"      -> "com.mysql.jdbc.Driver",
  "h2"         -> "org.h2.Driver"
)
val driver = drivers(dialect)
// driver: String = "com.mysql.jdbc.Driver"

---

If you are expecting malformed inputs, you can also use a match statement:

"jdbc:postgresql:something" match {
  case s"jdbc:$dialect:$rest" => Some(dialect)
  case _                      => None
}
// Option[String] = Some("postgresql")

---

import PartialFunction._  // condOpt

val drivers = Map( 
  "mysql" -> "mysql driver",
  "h2" -> "h2 driver" 
  // ... 
)
val pattern = "^jdbc:(\\w+):.*".r

def resolveDriver(url: String) = condOpt(url) { 
  case pattern(dbms) => drivers.get(dbms) 
}.flatten.getOrElse(throw new IllegalArgumentException)