How to handle csv file upload?

Hi, I am developing a plugin where you can upload a csv file to bulk create users based on data in the csv file. So far this is what I’ve managed to display the velocity template, with a form as such:

<form id="form" action="#">
                <input type="file" id="file-input" accept=".csv"/>
                <button type="submit" value="Submit">Submit</button>

However, I’m stuck on the action java class. How do I handle the csv file upon submitting the form (extract the data from the csv file)?
Thank you