Summation of Tax amount field in message mapping

Hi All,

Requirement is PI has to sum up the amount value in message mapping

E1EDP01 ->E1EDP04 ->MWSKZ-SD--> MWSBT(amount value).

E1EDP04 SD occurs 5 times in one line item and during summation 3rd one in sequence should be ignored and rest all 4 should be summed up.

Invoice Idoc may have multiple line items.Please let me know how to achieve this in java code.

Regards,

Karthiga