What is the best way to convert a byte array to an IntStream?

Question

Java 8 has java.util.stream.Stream and java.util.stream.IntStream types. java.util.Arrays has a method

IntStream is = Arrays.stream(int[])

but no such method to make an IntStream from a byte[], short[] or char[], widening each element to an int. Is there an idiomatic/preferred way to create an IntStream from a byte[], so I can operate on byte arrays in a functional manner?

I can of course trivially convert the byte[] to int[] manually and use Arrays.stream(int[]), or use IntStream.Builder:

public static IntStream stream(byte[] bytes) {
   IntStream.Builder isb = IntStream.builder();
   for (byte b: bytes) 
       isb.add((int) b); 
   return isb.build();
}

but neither is very functional due to the copying of the source.

There also does not seem to be an easy way to convert an InputStream (or in this case an ByteArrayInputStream) to an IntStream, which would be very useful for processing InputStream functionally. (Glaring omission?)

Is there a more functional way that is efficient and does not copy?

Answer 1

 byte[] bytes = {2, 6, -2, 1, 7};
 IntStream is = IntStream.range(0, bytes.length).map(i -> bytes[i]);

 ByteArrayInputStream inputStream = new ByteArrayInputStream(bytes);
 IntStream is2 = IntStream.generate(inputStream::read).limit(inputStream.available());

Answer 2

public static IntStream stream(byte[] bytes) {
    ByteBuffer buffer = ByteBuffer.wrap(bytes);
    return IntStream.generate(buffer::get).limit(buffer.remaining());
}

(This can easily be changed to take ints from the ByteBuffer, ie. 4 bytes to the int.)

For InputStream, if you want to consume it eagerly, just read it into a byte[] and use the above. If you want to consume it lazily, you could generate an infinite InputStream using InputStream::read as a Consumer (plus exception handling) and end it when you've reached the end of the stream.

Concerning

but neither is very functional due to the copying of the source

I don't see why that makes it non functional.

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