Code to read a uploaded file in any java listener class

I have a requirement to upload a json file through embedded html on start of process and at same time I need to read that file and make those json data as process variable.

How to read those json file on start using java and create process variable from those file data.
please help me

You can upload a file using the existing controls and use a java delegate to parse the json and set the variables using the java API.

how I will read this json file using java delegate from camunda. my requirment is on start only I should upload a file and same time I read this file and set the variable.