Convert hex to binary

hexStr2Bin.java

/**
 * Converts hex string to byte array.
 *
 * @param hex hex string. if invalid, return null.
 * @return binary data.
 */
private static byte[] hexStr2Bin(String hex) {
    int sz = hex.length()/2;
    byte[] b = new byte[hex.length()/2];

    for (int i=0;i<sz;i++) {
        try {
            b[i] = (byte)Integer.parseInt(hex.substring(i*2, i*2+2), 16);
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }
    return b;
}