How do I identify if the string contains a special character which cannot be stored using a utf8-mb4 character set
public static synchronized String toHex(byte [] buf){
    StringBuffer strbuf = new StringBuffer(buf.length * 2);
    int i;
    for (i = 0; i < buf.length; i++) {
        if (((int) buf[i] & 0xff) < 0x10){
            strbuf.append("0");
        }
        strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
    }
    return strbuf.toString();
}

public synchronized static byte[] hexToBytes(String hexString) {
    HexBinaryAdapter adapter = new HexBinaryAdapter();
    byte[] bytes = adapter.unmarshal(hexString);
    return bytes;
}