// This is a function in class DepartmentBean which check if element already exist in container:

bool f;
public void addIfAbsent(UserBean userBean) {
            if (users.stream().anyMatch(x -> x.getUsername().equals(userBean.getUsername()))) {
                f = false;
            } else {
                f = true;
                users.add(userBean);
            }
        }
    }

//In my servlet I am trying to send Message of succeseful registration(if f=false, their's no username with the same name):

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    try {
                doAll(request, response);
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
public static void doAll(HttpServletRequest request, HttpServletResponse response) throws Exception {
             DepartmentBean dp = new DepartmentBean();
             UserBean user = new UserBean();
             DepartmentBean departmentBean = read();
                String userName = request.getParameter("username");
                String password = request.getParameter("password");
                user.setPassowrd(password);
                user.setUsername(userName);
                departmentBean.addIfAbsent(user);
    if(dp.f = true)
    {
        String Message = "msg";
        /*Set attribute msg of Message*/
        request.setAttribute(Message, "msg");
        RequestDispatcher rd=request.getRequestDispatcher("index.jsp");
         rd.forward(request, response);
         write(departmentBean);
    }
        }
        public static DepartmentBean read() throws JAXBException {
            JAXBContext context = JAXBContext.newInstance(DepartmentBean.class, UserBean.class);
            Unmarshaller unmarshaller = context.createUnmarshaller();
            return (DepartmentBean) unmarshaller.unmarshal(new StreamSource(new File("1.xml")));
        }
        public static void write(DepartmentBean department) throws JAXBException {
            JAXBContext context = JAXBContext.newInstance(DepartmentBean.class, UserBean.class);
            Marshaller marshaller = context.createMarshaller();
            marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);
            marshaller.marshal(department, new File("1.xml"));
        }
    }
// In my html I added this jsp code:

<%>
    String s = "msg";
    if (s == request.getAttribute("Message"))
    {
        out.println("<p>Succesful</p>");
    }
    else
    {
        out.println("<p>Error reg</p>");
    }
    <%>


  /*  When I check the xml file the record is succesful but their's no "Succeful" paragraph in my html. It always retuns null, the "Error reg" paragraph. */