Servlet is cross referencing variable values to generate Filled PDF

Hi Folks

we have created a Maven Project to define a Servlet, which is calling FormService.importData method to prefill a PDF with AEMFD Data Document.

Issue is when multiple requests are sent and any time when 1 request is yet to complete and in concurrent another request is received by Servlet then AEMFD Data Document of Request 1 is overwritten by Request 2 and we are getting 2 PDFs with same data prefilled. 

This is causing lot of issues to customers who are being exposed to another customer data.

We are using SlingAllMethodsServlet extended in Servlet and no internal methods are static.

Any guidance

Manu