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ScalaでGzipによる圧縮/展開を行う。

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環境

  • Mac OS X Version 10.10.2
  • Scala 2.11.5
  • sbt 0.13.7

準備

/root/to/project/path
   |-- build.sbt
   |-- src
   |    |-- main
   |    |    |-- scala
   |    |    |    |-- GZIP.scala
   |    |-- test
   |    |    |-- scala
   |    |    |    |-- GZIPSpec.scala
build.sbt
name := "gzip"                                                                                                                                                    

version := "1.0"

scalaVersion := "2.11.5"

scalacOptions ++= Seq("-Xlint", "-deprecation", "-unchecked", "-feature", "-Xelide-below", "ALL")

libraryDependencies ++= Seq(
  "org.scalaz" %% "scalaz-core" % "7.1.1",
  "org.specs2" %% "specs2" % "2.4.1"
)

実装

src/main/scala/GZIP.scala
import java.io.{BufferedReader, ByteArrayInputStream, ByteArrayOutputStream, InputStreamReader}
import java.nio.charset.Charset
import java.util.zip._

import scala.util.control.Exception._
import scalaz.Scalaz._

object GZIP {

  def compress(source: String, charsetName: String): Either[Throwable, Array[Byte]] = {
    val buffer = new ByteArrayOutputStream()
    def compressString(source: String, charset: Charset): Either[Throwable, Unit] = {
      val gzos = new GZIPOutputStream(buffer)
      allCatch andFinally {
        gzos.close()
      } either {
        gzos.write(source.getBytes(charset))
      }
    }
    def toByteArray: Either[Throwable, Array[Byte]] = {
      allCatch andFinally {
        buffer.close()
      } either {
        buffer.toByteArray()
      }
    }
    for {
      r1 <- getCharset(charsetName)
      r2 <- compressString(source, r1)
      r3 <- toByteArray
    } yield r3
  }

  def decompress(data: Array[Byte], charsetName: String): Either[Throwable, String] = {
    def decompressByteArray(data: Array[Byte], charset: Charset): Either[Throwable, String] = {
      val bais = new ByteArrayInputStream(data)
      val gzis = new GZIPInputStream(bais)
      val reader = new InputStreamReader(gzis)
      val in = new BufferedReader(reader)
      val sb = new StringBuilder
      allCatch andFinally {
        in.close()
        reader.close()
        gzis.close()
        bais.close()
      } either {
        Iterator continually {
          in.readLine()
        } takeWhile {
          _ != null
        } foreach {
          sb.append(_)
        }
        sb.result
      }
    }
    for {
      r1 <- getCharset(charsetName)
      r2 <- decompressByteArray(data, r1)
    } yield r2
  }

  private def getCharset(charsetName: String) =
    allCatch either { Charset.forName(charsetName) }
}
src/test/scala/GZIPSpec.scala
import org.specs2.mutable.Specification

class GZIPSpec extends Specification {

  "GZIP" should {
    "compress -> decompress" in {
      val r1 = GZIP.compress("あいうえお", "UTF-8")
      val c = r1.fold(x => Array[Byte](0), identity)
      val r2 = GZIP.decompress(c, "UTF-8")
      val d = r2.fold(x => "", identity)
      d must_== "あいうえお"
    }
  }
}

実行

$ sbt '~test-only GZIPSpec'

参考

http://stackoverflow.com/questions/3627401/gzipinputstream-to-string

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