The fact that your JSP is in a source folder seems to indicate that it will be placed in
/WEB-INF/classes/view/admin/
Which is really not where
String addressPath = "/../view/admin/adminPage.jsp";
is pointing it to.
getRequestDispatcher
returns null
if the Servlet container cannot return a RequestDispatcher
for the given path.
JSPs shouldn't really be under /WEB-INF/classes
. Put them in a dedicated folder like /WEB-INF/jsp/view
and access them there.
You could then access it with
String addressPath = "/WEB-INF/jsp/view/admin/adminPage.jsp";