Scala: InputStream to Array[Byte]

Question

With Scala, what is the best way to read from an InputStream to a bytearray?

I can see that you can convert an InputStream to char array

Source.fromInput         


        

Answer 1

How about:

Stream.continually(is.read).takeWhile(_ != -1).map(_.toByte).toArray

Update: Use LazyList instead of Stream (since 2.13.x deprecated)

LazyList.continually(is.read).takeWhile(_ != -1).map(_.toByte).toArray

Answer 2

How about buffered version of solution based on streams plus ByteArraOutputStream to minimize boilerplate around final array growing?

val EOF: Int = -1

def readBytes(is: InputStream, bufferSize: Int): Array[Byte] = {
  val buf = Array.ofDim[Byte](bufferSize)
  val out = new ByteArrayOutputStream(bufferSize)

  Stream.continually(is.read(buf)) takeWhile { _ != EOF } foreach { n =>
    out.write(buf, 0, n)
  }

  out.toByteArray
}

Answer 3

With Scala IO, this should work:

def inputStreamToByteArray(is: InputStream): Array[Byte] = 
   Resource.fromInputStream(in).byteArray

Answer 4

Just removed bottleneck in our server code by replacing

Stream.continually(request.getInputStream.read()).takeWhile(_ != -1).map(_.toByte).toArray

with

org.apache.commons.io.IOUtils.toByteArray(request.getInputStream)

Or in pure Scala:

def bytes(in: InputStream, initSize: Int = 8192): Array[Byte] = {
  var buf = new Array[Byte](initSize)
  val step = initSize
  var pos, n = 0
  while ({
    if (pos + step > buf.length) buf = util.Arrays.copyOf(buf, buf.length << 1)
    n = in.read(buf, pos, step)
    n != -1
  }) pos += n
  if (pos != buf.length) buf = util.Arrays.copyOf(buf, pos)
  buf
}

Do not forget to close an opened input stream in any case:

val in = request.getInputStream
try bytes(in) finally in.close()

Answer 5

In a similar vein to Eastsun's answer... I started this as a comment, but it ended up getting just a bit to long!

I'd caution against using Stream, if holding a reference to the head element then streams can easily consume a lot of memory.

Given that you're only going to read in the file once, then Iterator is a much better choice:

def inputStreamToByteArray(is: InputStream): Array[Byte] =
  Iterator continually is.read takeWhile (-1 !=) map (_.toByte) toArray

Answer 6

With better-files, you can simply do is.bytes