Data compression in Scala

Question

Here below is my attempt to implement a class that provides functionality for compressing/decompressing strings:

object GZipHelper {

  def deflate(txt: String): Try[String] = {
    try {
      val arrOutputStream = new ByteArrayOutputStream()
      val zipOutputStream = new GZIPOutputStream(arrOutputStream)
      zipOutputStream.write(txt.getBytes)
      new Success(Base64.encodeBase64String(arrOutputStream.toByteArray))
    } catch {
      case _: e => new Failure(e)
    }
  }

  def inflate(deflatedTxt: String): Try[String] = {
    try {
      val bytes = Base64.decodedBase64(deflatedTxt)
      val zipInputStream = GZIPInputStream(new ByteArrayInputStream(bytes))
      new success(IOUtils.toString(zipInputStream))
    } catch {
      case _: e => new Failure(e)
    }
  }
}

As you can see, the finally blocks that close GZIPOutputStream and GZIPInputStream are missing... how could I implement this in the ''scala'' way? How could I improve the code?

Answer 1

Since you're using the "old fashioned" try statement and explicitly turning it into a scala.util.Try, there really is no reason not to add a finally block after your try.

In this specific case though, there is little point in closing, for example, your ByteArrayInputStream - it's not really an open resource and does not need to be closed. In which case you can simplify your code and make it much more idiomatic this way:

def inflate(deflatedTxt: String): Try[String] = Try {
   val bytes = Base64.decodedBase64(deflatedTxt)
   val zipInputStream = GZIPInputStream(new ByteArrayInputStream(bytes))
   IOUtils.toString(zipInputStream)
}

I personally would not declare bytes and zipInputStream since they're only used once, but that's a matter of preference.

The trick here is having a finally block with a call to scala.util.Try.apply - I'm not sure that's possible without going through a call to map that doesn't actually modify anything, which seems like a bit of an oversight to me. I was expecting to see an andThen or eventually method in scala.util.Try, but it doesn't seem to be there (yet?).