Cannot call sendRedirect() after the response has been committed

@WebServlet("/Controller")
public class Controller extends HttpServlet{
 
    private static final long serialVersionUID = 1L;
    private boolean flag = false;
    private List<String> name;
 
    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        if (flag == false){
            process(request, response);
            flag=true;
        }
        RequestDispatcher view = request.getRequestDispatcher("form.jsp");
        view.forward(request, response);
    }
 
 
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        process(request, response);
        flag=true;
        response.sendRedirect("Controller");
    }
    
    @Override
    public void init() throws ServletException {
        name = new ArrayList<>();
    }
    
    
    
    private void  process(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
        req.setCharacterEncoding("UTF-8");
        resp.setContentType("text/html;charset=utf-8");
        HttpSession session = req.getSession();
        String button = req.getParameter("submit");
        if(button.equals("add")){
            name.add(req.getParameter("name"));
            session.setAttribute("name", name);
            req.getRequestDispatcher("form.jsp").forward(req, resp);
        }else if(button.equals("delete")){
            name.removeAll(name);
            req.getRequestDispatcher("form.jsp").forward(req, resp);
        }
        
        
    }
    
    
}