Refreshing a page without going to it?

Question

Java

Dear community members, I ask you to help me understand the following, I have a parent page index.jsp, from it I follow the link to another page, for example reg.jsp. On reg.jsp, the user registers and closes the page

window.close().

In this case, new user data should appear on the parent index.jsp page. How to do it?

response.sendRedirect(redirectURL)

will not work because it opens a new window, and I need an update in the already open index.jsp. Is this even possible? Who has any thoughts on this?