Java readInt method returns LittleEndian rather than BigEndian value of Int in Scala

Question

I'm using Kryo to deserialize a class originally serialized in Spark. Kryo writes all of its primitives in BigEndian format, but when I try to deserialize the values on another machine, the value is being returned as if it were LittleEndian.

Underlying method in Kryo:

public int readInt () throws KryoException {
    require(4); // Does a basic positionality check that passes in this case
    byte[] buffer = this.buffer;
    int p = this.position;
    this.position = p + 4;
    return buffer[p] & 0xFF //
        | (buffer[p + 1] & 0xFF) << 8 //
        | (buffer[p + 2] & 0xFF) << 16 //
        | (buffer[p + 3] & 0xFF) << 24;
}

This returns the value 0x70000000. But when my program (in Scala) uses Kryo's readByte method:

public byte readByte () throws KryoException {
    if (position == limit) require(1);
    return buffer[position++];
}

and reads the bytes individually, like this:

  val a = input.readByte()
  val b = input.readByte()
  val c = input.readByte()
  val d = input.readByte()
  val x = (a & 0xFF) << 24 | (b & 0xFF) << 16 | (c & 0xFF) << 8 | d & 0xFF

Then I get 0x70 for x. I don't understand what's happening here. Is it some kind of conversion issue between Scala and Java, or something to do with Kryo and the underling byte array?

Answer 1

The code you wrote:

  val a = input.readByte()
  val b = input.readByte()
  val c = input.readByte()
  val d = input.readByte()
  val x = (a & 0xFF) << 24 | (b & 0xFF) << 16 | (c & 0xFF) << 8 | d & 0xFF

is converting bytes to int in the wrong way. If you closely inspect the readInt() method you'll see that you've switched the order.

  val x = (a & 0xFF) | (b & 0xFF) << 8 | (c & 0xFF) << 16 | d & 0xFF << 24;

would be the correct way to write this.