how to pass a input param to custom servlet

hi all,
is there a way to pass a input parameter of expression to a custom servlet?

I'm trying to rewrite the excel download plugin("getdatasubsetdownloadlinkfromrule").
in the previous plugin, we pass the rule name and input into the expression and dynamically get the datasubset in the servlet.
in the version 17.1, it doesn't support any more.

I try to directly pass the json string of the datasubset into the expression and pass the json string to servlet. However, there is a problem.
After appending the json string, the http URL is more than the max length.

Does Appian have a way to pass a input parameter of expression to a custom servlet, or is there a global context to share this input param?

OriginalPostID-268491