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In Scala, given a binary file, I am interested in retrieving a list of Array[Byte] items.

For example, the binary file has items delimited by the characters/bytes 'my-delimiter'.

How can I get a list of Array[Byte] for each item?

Functional solution, with help of java.nio:

import java.nio.file.Files, Paths

object Main 

 private val delimiter = 'n'.toByte

 def main(args: Array[String]): Unit = 
 val byteArray = Files.readAllBytes(Paths.get(args(0)))

 case class Accumulator(result: List[List[Byte]], current: List[Byte])

 val items: List[Array[Byte]] = byteArray.foldLeft(Accumulator(Nil, Nil)) 
 case (Accumulator(result, current), nextByte) =>
 if (nextByte == delimiter)
 Accumulator(current :: result, Nil)
 else
 Accumulator(result, nextByte :: current)
 match 
 case Accumulator(result, current) => (current :: result).reverse.map(_.reverse.toArray)
 
 items.foreach(item => println(new String(item)))
 

This solution is expected to have poor performance though. How important is that for you ? How many files, of what size and how often will you read? If performance is important, than you should rather use input streams and mutable collections:

import java.io.BufferedInputStream, FileInputStream

import scala.collection.mutable.ArrayBuffer

object Main 

 private val delimiter = 'n'.toByte

 def main(args: Array[String]): Unit = 
 val items = ArrayBuffer.empty[Array[Byte]]
 val item = ArrayBuffer.empty[Byte]
 val bis = new BufferedInputStream(new FileInputStream(args(0)))
 var nextByte: Int = -1
 while ( nextByte = bis.read(); nextByte != -1) 
 if (nextByte == delimiter) 
 items.append(item.toArray)
 item.clear()
 else 
 item.append(nextByte.toByte)
 
 
 items.append(item.toArray)
 items.foreach(item => println(new String(item)))
 bis.close()