Java HotSpot Virtual Machine

Hi everibody.

I need to map the struct bellow:

//This is the original struct. I need to do the same, but using JNA
 struct fp_print_data {
    size_t length;
    unsigned char data[0];
    };

I tried to do the class bellow, but not worked well.

//This is what i did, but doesn't work.
public class JCLeitorBiometricoStructurePrintData extends Structure {
    public int length;
    public byte data;
}

How can I map the "size_t" C type using JNA?
And I need to be sure that the var "char data[0]" is correctly mapped, if it isn't.

Could someone help me?