Confluence plugin how to read csv file data after submitting file input form?

I am developing a plugin on Confluence Server where I can bulk create users based on the information in a csv file.The csv file has the following columns:

• Username
• Fullname
• Email
• Password
• GroupsToBeAddedInto

So far, I've managed to display a Velocity template, using the web-item and xwork modules, with a form as such:

<form class="aui" id="form" method="post" action="#"><label for="file-input">Upload CSV file:</label><input class="upfile" type="file" id="file-input" name="file-input" accept=".csv"><button id="submit-btn" type="submit" value="Submit">Submit</button></form>

Right now, I'm stuck at the form action. How do I write the action class such that when someone uploads the csv file and clicks submit, the information in the csv file will be read to generate new users?

Thank you!