Dynamically loading content through Groovy server page upon form submit

I have a Groovy project (vanilla; no Grails) with an index.gsp that takes form input from the user and sends it in a POST request to a Groovy script. The form is set up like this:

<form action="somewhere" method="POST" enctype="multipart/form-data">
    // some other inputs
    <input type="submit"/>
</form>

Is there any way (ideally not using Javascript) to dynamically load content on the same page after the user submits? Just something simple, like a string containing whatever the user typed. It seems like Grails has plenty of options, but unfortunately I can't use it.