response.sendRedirect("error404.jsp");    // no path here !!!

String addressPath = "/WEB-INF/results/admin/adminPage.jsp";
    response.sendRedirect(addressPath);   // with path !!!

HTTP Status 404 -

type Status report

message

description The requested resource is not available.

Apache Tomcat/7.0.50

String addressPath = "/WEB-INF/results/admin/adminPage.jsp";
response.sendRedirect(addressPath);   // with path !!!

Location: http://whateverhost.com/WEB-INF/results/admin/adminPage.jsp

response.sendRedirect("error404.jsp");    // no path here !!!

Location: http://whateverhost.com/context-path/error404.jsp

<servlet>
    <servlet-name>adminPage</servlet-name>
    <jsp-file>/WEB-INF/results/admin/adminPage.jsp</jsp-file>
  </servlet>
  <servlet-mapping>
    <servlet-name>adminPage</servlet-name>
    <url-pattern>/adminPage/*</url-pattern>
</servlet-mapping>

response.sendRedirect("./adminPage/");