convert a byte array to string

Question

My Scala code received a binary from byte stream,it looks like [61 62 63 64].The content is "abcd". I use toString to convert it p, but failed. How do I print it as string ?

Hickey

Try to parse each number as a char and concate them to have a string – Rigidify

Converting byte array to string – Niles

Possible duplicate of Byte array to String and back.. issues with -127 – Steinberg

Answer 1

You could convert the byte array to a char array, and then construct a string from that

scala> val bytes = Array[Byte]('a','b','c','d')
bytes: Array[Byte] = Array(97, 98, 99, 100)

scala> (bytes.map(_.toChar)).mkString 
res10: String = abcd

scala> 

Trish

As @michael-hill already mentioned in a comment below, this can cause problems because it assumes you're working in ASCII and not UTF-8 or some other character encoding. If you were to try to convert the following (proper) UTF-8 byte array to a String... val msg = Array[Byte](-17, -69, -65, 72, 101, 108, 108, 111) (msg.map(_.toChar)).mkString You would get something that looked very weird and not the expected "Hello" that you would get from this: new String(msg) – Debag

As @Trish said, this is really bad advice. Please don't do this. This can lead to silent data corruption and other hard to track down bugs – Cardoon

println("🍕".getBytes(StandardCharsets.UTF_8).length) > 4 – Starter

Answer 2

You can always convert the byte array to a string if you know its charset,

val str = new String(bytes, StandardCharsets.UTF_8)

And the default Charset would used if you don't specify any.

Wheelock

Curious which method is better, (bytes.map(_.toChar)).mkString or new String(bytes)? – Ganister

@Ganister this is perhaps a bit late for you; but the two could potentially produce different results. UTF-8 is a variable width encoding, so a single character could be encoded with a single byte or multiple. UTF-8 encodes ASCII characters in the same way (eg. A is represented by 65 in both) but most (maybe all?) other characters with multiple bytes. In short; they're the same if your string contains only ASCII characters but otherwise will produce different results. – Landa

@MichealHill assuming that the stream is a UTF-8 stream is a fairly reasonable for text payloads nowadays. The original question asked to print out a 'binary' byte stream, this particular case does not imply a string encoding. This is why it's best to provide an encoding when you're transmitting strings. (You can use frequency analysis to infer a probable string encoding if you have a text stream with no indicated encoding) – Trish

Answer 3

The bytes to string function I was looking for was where each byte was just a numeric value represented as a string, without any implied encoding. Thanks to the suggestions supplied here, I ended up with the following function which works for my purposes. I post it here incase it useful to someone else.

  def showBytes(bytes: Array[Byte]):String = {
    bytes.map(b => "" + b.toInt).mkString(" ")
  }

This function will return a string containing numeric values separated by spaces.

Tease

Two things: 1-I don't see what all the type conversions are for. Why not just bytes.mkString(" ")? and 2-This answer is out of place. It doesn't answer the question asked. – Fleshpots