Java-byte []到int的转换，反之亦然

Question

I am porting some php code as well as python code, which are two functions. The purpose of them is parsing an integer to a byte array and vice versa. However it worked for a while, but now I get invalid integer errors.

I got the following python snippet which I converted to Java:

def _deAdjustId(val):
    if sys.version_info >= (3,0):
        valEnc = val.encode('latin-1') if type(val) is str else val
    else:
        valEnc = val
    return int(binascii.hexlify(valEnc), 16)

And my Java code:

private static int deAdjustId(byte[] val) {
    String valEnc;
    try {
        valEnc = new String(val, "iso-8859-1");
    } catch (UnsupportedEncodingException e) {
        valEnc = new String(val);
    }
    return Integer.parseInt(BinAscii.hexlify(valEnc.getBytes()), 16);
}

The error given here is the following:

caught exception: Invalid int: "325FC398C3AB"

Does this mean that the integer value is too big, or what is the problem?

Answer 1

valEnc.getBytes() will convert the String to bytes using the host platform's default encoding, which is going to be either UTF-16LE (in Windows) or UTF-8 (all other platforms, including yours).

Your String contains ISO 8859-1 characters, but any of those characters with values above 127 are being decoded as multiple bytes by valEnc.getBytes() . To fix this, use valEnc.getBytes(StandardCharsets.ISO_8859_1) . Then you will be guaranteed to get one byte per character.

However, that raises the question of why you would bother using String in the first place. You already have a byte array whose bytes each represent an ISO 8859-1 character. You should remove valEnc from your method completely.

In fact, there is no reason to convert the bytes to hex and then parse them. You can just convert four bytes to an int with this:

return ByteBuffer.wrap(val).getInt();

See the documentation for ByteBuffer for more information, particularly the getInt method.

Update: It seems val has no guarantees regarding its size, so you'll want to account for that:

if (val == null) {
    return 0;
}

if (val.length >= 4) {
    return ByteBuffer.wrap(val).getInt();
}

ByteBuffer buffer = ByteBuffer.allocate(4);
buffer.position(4 - val.length);
buffer.put(val);
buffer.rewind();
return buffer.getInt();

Answer 2

Python int is like BigInteger in Java:

private static BigInteger deAdjustId(byte[] val) {
    String valEnc;
    try {
        valEnc = new String(val, "iso-8859-1");
    } catch (UnsupportedEncodingException e) {
        valEnc = new String(val);
    }
    return new BigInteger(BinAscii.hexlify(valEnc.getBytes()), 16);
}

or even:

private static BigInteger deAdjustId(byte[] val) {
    return new BigInteger(val);
}