/**
 * Convert byte array to hex format string (e.g. "01,02,FE,FF").
 */
public static final String toHexString(byte[] data) {
    final int len = data.length;
    if (len == 0) {
        return "";
    }
    if (len == 1) {
        return String.format("%02X", data[0]);
    }
    StringBuilder builder = new StringBuilder(len * 3 - 1);
    builder.append(String.format("%02X", data[0]));
    for (int i = 1; i < len; ++i) {
        builder.append(String.format(",%02X", data[i]));
    }
    return builder.toString();
}