Parse C byte array into Java ByteBuffer.

Question

I'm parsing a byte array which contains variables of different types. I'm getting this array from HID connected to my phone. Array was made by C programmer. I'm trying to parse it using ByteBuffer class:

byte[] buffer = new byte[64];
if(connection.bulkTransfer(endpoint, buffer, 64, 1000) >= 0)
{
    ByteBuffer byteBuffer = ByteBuffer.wrap(buffer);
    char mId = byteBuffer.getChar();
    short rId = byteBuffer.getShort();
    // ............................
}

But the values of this variables are not correct. Can anyone please tell me what i'm doing wrong?

Answer 1

There are systems with LitteEndian Byte order and BigEndian.

java uses BigEndian.

If the c programmer wrote the byte array in Little endian, you could use DataInputStream based on an Appache LittleEndianInputStream:

LittleEndianInputStream leis = new LittleEndianInputStream(is);
DataInputStream dis = new DataInputStream(leis);

int i1 = dis.readInt();
short s2 = dis.readShort();

If you and your colleague define a binary interface (file, or byte array) you always should force a speciifc byte order (Either little or big endian).

Answer 2

If byte order (little vs big endian) is the issue, you can set the byte order for the ByteBuffer to native without changing all of the program:

ByteBuffer byteBuffer = ByteBuffer.wrap(buffer);
byteBuffer.order(ByteOrder.nativeOrder()); // Set native byte order
char mId = byteBuffer.getChar();
short rId = byteBuffer.getShort();

On the other hand, if you find ByteBuffer objects more convenient than byte arrays, tell the C programmer to return you a direct byte buffer instead of an array: easier for all parties and probably more efficient.