A sample code of gzip in Scala. API of gzip is included in the package java.util.zip. It provides GZIPOutputStream and GZIPInputStream, the subclasses of DeflatterOutputStream and InflatterInputStream, respectively. GZIPOutputStream compresses data into a given output stream and GZIPInputStream decompresses data from an input one.

gzip-sample.scala

import java.io._
import java.util.zip._

val pi = new PipedInputStream        
val po = new PipedOutputStream(pi)
val zo = new GZIPOutputStream(po)
val zi = new GZIPInputStream(pi)
val w  = new PrintWriter(zo)
val r  = new BufferedReader(new InputStreamReader(zi))

pw.println("Hello, world.")
pw.close

println(r.readLine)

gzip.scala

import java.io._
import java.util.zip._

/** Gzcat
 */
object gzcat extends App {
  private val buf = new Array[Byte](1024)

  try {
    for (path <- args) {
      try {
	var in = new GZIPInputStream(new FileInputStream(path))
	var n = in.read(buf)
	while (n >= 0) {
	  System.out.write(buf, 0, n)
	  n = in.read(buf)
	}
      }
      catch {
	case _:FileNotFoundException =>
	  System.err.printf("File Not Found: %s", path)
	case _:SecurityException =>
	  System.err.printf("Permission Denied: %s", path)
      }
    }
  }
  finally {
    System.out.flush
  }
}


/** gzip
 */
object gzip {
  private val buf = new Array[Byte](1024)

  def gzip(path: String) {
    val src = new File(path)
    val dst = new File(path ++ ".gz")

    try {
      val in  = new BufferedInputStream(new FileInputStream(src))
      try {
	val out = new GZIPOutputStream(new FileOutputStream(dst))
	try {
	  var n = in.read(buf)
	  while (n >= 0) {
	    out.write(buf, 0, n)
	    n = in.read(buf)
	  }
	}
	finally {
	  out.flush
	}
      } catch {
	case _:FileNotFoundException =>
	  System.err.printf("Permission Denied: %s", path ++ ".gz")
	case _:SecurityException =>
	  System.err.printf("Permission Denied: %s", path ++ ".gz")
      }
    } catch {
      case _: FileNotFoundException =>
	System.err.printf("File Not Found: %s", path)
      case _: SecurityException =>
	System.err.printf("Permission Denied: %s", path)
    }
  }

  def main(filenames: Array[String]) {
    if (filenames.length == 0) {
      System.err.println("Usage: scala gzip file...")
      System.exit(1)
    }
    else {
      filenames.foreach(gzip(_))
    }
  }
}


object gunzip {
  private val buf = new Array[Byte](1024)

  /**
   * gunzip
   *
   * @param PATH: the path name without the extentson ".gz"
   *   You have to check if there is no file named as PATH
   * before you invode this method, or the file is going
   * to be overwritten.
   */
  def gunzip(path: String) {
    val src = new File(path ++ ".gz")
    val dst = new File(path)

    try {
      val in  = new GZIPInputStream(new FileInputStream(src))
      try {
	val out = new BufferedOutputStream(new FileOutputStream(dst))
	try {
	  var n = in.read(buf)
	  while (n >= 0) {
	    out.write(buf, 0, n)
	    n = in.read(buf)
	  }
	}
	finally {
	  out.flush
	}
      } catch {
	case _:FileNotFoundException =>
	  System.err.printf("Permission Denied: %s", path)
	case _:SecurityException =>
	  System.err.printf("Permission Denied: %s", path)
      }
    } catch {
      case _: FileNotFoundException =>
	System.err.printf("File Not Found: %s", path ++ ".gz")
      case _: SecurityException =>
	System.err.printf("Permission Denied: %s", path ++ ".gz")
    }
  }

  def main(filenames: Array[String]) {
    if (filenames.length == 0) {
      System.err.println("Usage: scala gunzip gz-file...")
      System.exit(1)
    }
    else {
      val eitherNames = 
	for (name <- filenames)
	  yield if (name.endsWith(".gz")) {
		    val noExtension = name.drop(3)
		    val src = new File(name)
		    val dst = new File(noExtension)
		    if (! src.exists)
		      Left(new FileNotFoundException(name))
		    else if (dst.exists)
		      Left(new IOException("file already exists: " + noExtension))
		    else
		      Right(noExtension)
	        } else {
		  Left(new IOException("file is not gzip: " + name))
		}
      if (eitherNames.forall {_.isRight}) {
	for (Right(noExt) <- eitherNames) {
	  gunzip(noExt)
	}
      }
      else {
	for (Left(e) <- eitherNames)
	  throw e
      }
    }
  }
}