Amazon の Product Advertising API を使う

Product Advertising API

Amazonの商品情報を検索できるAPI

公式のJava実装

Scalaで書いてみる

amazon.scala

import java.io.UnsupportedEncodingException
import java.net.URLEncoder
import java.text.SimpleDateFormat
import java.util.{TimeZone, Calendar}
import javax.crypto.Mac
import javax.crypto.spec.SecretKeySpec
import org.apache.commons.codec.binary.Base64
import scala.collection.SortedMap
import scala.collection.immutable.TreeMap
import scala.io.Source
import scala.collection.JavaConversions._

/**
 * Created by FScoward on 2014/11/21.
 */
class Amazon {
  private val accessKey = "秘密"
  private val secretAccessKey = "秘密"
  private val HMAC_SHA_256 = "HmacSHA256"
  private val UTF8_CHARSET = "UTF-8"
  private val REQUEST_URI = "/onca/xml"
  private val REQUEST_METHOD = "GET"
  private val endpoint = "ecs.amazonaws.jp"

  // 初期化
  val mac = {
    val secretAccessKeyBytes = secretAccessKey.getBytes(UTF8_CHARSET)
    val secretKeySpec = new SecretKeySpec(secretAccessKeyBytes, HMAC_SHA_256)
    val mac = Mac.getInstance(HMAC_SHA_256)
    mac.init(secretKeySpec)
    mac
  }

  def sign(params: Map[String, String]) = {
    val sortedParams = TreeMap.empty[String, String] ++ params ++ Map("AWSAccessKeyId" -> accessKey, "Timestamp" -> timestamp)
    val canonicalQS = canonicalize(sortedParams)
    val toSign = s"""$REQUEST_METHOD\n$endpoint\n$REQUEST_URI\n$canonicalQS"""
    val sig = percentEncodeRfc3986(hmac(toSign))
    val url = s"""http://$endpoint$REQUEST_URI?$canonicalQS&Signature=$sig"""
//    Source.fromURL(url)
    println(url)
  }

  // hmac 生成
  private def hmac(stringToSign: String) = {
    try {
      val data = stringToSign.getBytes(UTF8_CHARSET)
      val rawMac = mac.doFinal(data)
      new String(new Base64().encode(rawMac))
    } catch {
      case e: UnsupportedEncodingException => throw new RuntimeException(UTF8_CHARSET + "is unsupported!", e)
    }
  }

  // タイムスタンプ生成
  private def timestamp = {
    new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'") {
      this.setTimeZone(TimeZone.getTimeZone("GMT"))
    }.format(Calendar.getInstance.getTime)
  }

  // 整形
  private def canonicalize(sortedParamMap: SortedMap[String, String]) = {
    val builder = new StringBuilder
    sortedParamMap.entrySet().iterator().foreach{ kvpair => 
      builder.append(percentEncodeRfc3986(kvpair.getKey))
      builder.append("=")
      builder.append(percentEncodeRfc3986(kvpair.getValue))
      builder.append("&")
    }
    builder.deleteCharAt(builder.lastIndexOf("&"))
    builder.toString
  }

  // + * %7E を変換
  private def percentEncodeRfc3986(string: String): String = {
    try {
      URLEncoder.encode(string, UTF8_CHARSET)
        .replace("+", "%20")
        .replace("*", "%2A")
        .replace("%7E", "~")
    } catch {
      case e: UnsupportedEncodingException => string
    }
  }
}

Scalaっぽい書き方とは？
誰か教えて下さい。