java - Data get from ajax null in jsp -

i able data ajax using system.out.println. however, unable pass data servlet. shows null always.

here jquery:

      function expresscheck(number) {             var self=[];             for(i=1;i<=<%=itemcodelist.size()%>;i++) self[i-1] = document.getelementbyid("qtyguestnumber_" + i).value;                 $.ajax({                     url: "viewcategories.jsp",                     data: {"expressdata" : self[number-1]}                 });         };