A jsp file in subfolder in webContent is not accessing a servlet in package. Error 404 not found

In WebContent > indexPages(folder) > NavigationBar.jsp

   <li><a href="adminServlet"><span class="glyphicon glyphicon-user"></span> SignIn</a></li>

In JavaResources > src > accounts(package) > adminServlet.java

@WebServlet("/accounts/adminServlet")
public class adminServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;    

also i think sometimes eclipse not updating the files correctly , it is using old ones how to correct it. do i need server restart or build project or something else.. i am missing