Getting multiple values from feeder

Hi,

I am somehow unable to retrieve the multiple values from session.
my csv is:
productId,ProductType,city
1,a,b
2,c,d
3,e,f

Now In my single http request I want to randomly get multiple such rows

my urls is /getproducts/productId={$productId1},{$productId2}&city={$city1},{$city2},{$city3}…

but its saying that its unable to find those names in session.

What am I missing ?

Or is it better and more flexible to load the while csv (its 3 mb) in a Map and then build the query string on my own by using variable number of items.