How does web interface pull data from server?

_x000D_ _x000D_ I'm a student, and I'm trying to learn web development. For practice, I plan to make a fictional school website and the only feature it has is register students to the school. Student provides his name and when he clicks the "register" button, his name is inserted into the database. So I made index.html which only has a textbox and a button, and made an insert function in java that inserts student's name into the database. But the problem is, how does the web part call the insert function written in java? Is there a way to have java code on server side, and html/javascript/css for front-end for web UI? I know that the practice question I put out can be done using php, but in the future, I would like to make the front-end using things like Metro UI, and server side code can get complex, so I plan to keep it in java.