After some troubleshooting, I managed to come up with a solution in my JSP file:
<s:textfield name="confermaEmail" id="idConfermaEmail" size="30" onFocus="disablePaste()"/>
To achieve this, I implemented a JavaScript function:
function disablePaste(){
var input = document.getElementById("idConfermaEmail");
if (input)
input.onpaste = function(){return false;};
}
I tested this code on Internet Explorer 10 and Chrome browsers.
Additionally, as mentioned by @Andrea Ligios in another comment, it is also possible to utilize the onPaste event in Struts 2.
Edit: Upon further evaluation, using onFocus instead of onPaste proves to be more effective. The onPaste event only blocks pasting after the first instance, whereas onFocus prevents pasting immediately upon focus, before any paste occurs.