How to customize the change "task form template" under site -> Utilities ->templates using custom jsp file

Hi All,

         I have created custom variable (FileName) in the workflow task and trying to read the value of the custom variable using custom template jsp file. Please refer the below screenshot of the workflow task.

     How can I read the value that has been entered in the custom variable using custom jsp file ?

     Please find the attached custom jsp file that i'm trying to read the variable.

Thank you in Advance..