Scala: Idiomatic way to convert Map[String, String] to String

Question

I have a map that contains a few HTTP parameters that will be sent to an API.

val sortedParameters: SortedMap[String, String] = SortedMap(
        "oauth_nonce" -> nonce,
        "oauth_callback" -> callbackURL,
        "oauth_signature_method" -> signatureMethod,
        "oauth_consumer_key" -> consumerKey
      )

The above parameters have to be URL encoded and concatenated in the form key1=value1&key2=value2 etc. What would be the best idiomatic way to achieve this in Scala?

Whatever library you use to send the request, already has a way to set and encode the parameters. Don't reinvent the bicycle. — Dima
– Dima, Commented Jul 26, 2017 at 22:12
Don't convert to String unless for debug. See the other comment. — som-snytt
– som-snytt, Commented Jul 27, 2017 at 3:38

mrmcgreg · Accepted Answer · 2017-07-27 13:56:23Z

5

Pretty much the same as the other answer but including encoding.

scala> import scala.collection.immutable.SortedMap
import scala.collection.immutable.SortedMap

scala> val enc = (s: String) => java.net.URLEncoder.encode(s, "utf-8")
enc: String => String = $$Lambda$1060/160696258@6c796cc1

scala> val sortedMap = SortedMap("a" -> "b&&c means both b and c are true", "c" -> "d=1")
sortedMap: scala.collection.immutable.SortedMap[String,String] = Map(a -> b&&c means both b and c are true, c -> d=1)

scala> sortedMap.map(kv => s"${enc(kv._1)}=${enc(kv._2)}").mkString("&")
res2: String = a=b%26%26c+means+both+b+and+c+are+true&c=d%3D1

EDIT: And a more idiomatic destructuring from a comment:

sortedMap.map({ case (k, v) => s"${enc(k)}=${enc(v)}" }).mkString("&")
res2: String = a=b%26%26c+means+both+b+and+c+are+true&c=d%3D1

edited Jul 27, 2017 at 13:56

answered Jul 26, 2017 at 21:28

mrmcgreg

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1 Comment

som-snytt Over a year ago

for idiom, m.map { case (k, v) => s"${enc(k)}=${env(v)}" }.

prayagupadhyay · Accepted Answer · 2017-07-26 21:34:11Z

0

.map() on each elem to create k=v pattern then concat them using TraversableOnce#foldLeft(z)(op) or TraversableOnce#mkString(separator)

example,

scala> import scala.collection.SortedMap
import scala.collection.SortedMap

scala> val sortedParameters = SortedMap("a" -> 1, "b" -> 2, "c" -> 3)
sortedParameters: scala.collection.SortedMap[String,Int] = Map(a -> 1, b -> 2, c -> 3)

using mkString,

scala> sortedParameters.map(kv => kv._1 + "=" + kv._2).mkString("&")
res1: String = a=1&b=2&c=3

using foldLeft,

scala> sortedParameters.map(kv => kv._1 + "=" + kv._2)
                       .foldLeft(new String)((a, b) => { if(a.equals("")) b else a + "&" + b})
res2: String = a=1&b=2&c=3

edited Jul 26, 2017 at 21:34

answered Jul 26, 2017 at 21:17

prayagupadhyay

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