public class UserFormController implements Controller {
    public ViewModel process (Request request){
        Integer userId = Integer.valueOf(request.getParameter("userId"));
        return new ViewModel("/WEB-INF/userform.jsp").withAttribute("userId",userId );
    }
}

public class UpdateController implements Controller{
    private final UserService userService;

    public UpdateController(UserService userService) {
        this.userService = userService;
    }

    @Override
    public ViewModel process(Request request) {
        Integer userId = Integer.valueOf(request.getParameter("userId"));
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String email = request.getParameter("email");
      //  String role = request.getParameter("role");
        User user = User.from (userId,username,password,email);
        userService.update(userId);
       // User user = User.from(username, password, email, role);
        return new ViewModel("/WEB-INF/postProcPage.jsp").withAttribute("user",user);
    }
}

public class Factory {

    public static Connection getConnection() {

        Connection connection = null;
        try {
            Class.forName("org.h2.Driver");
            connection = DriverManager.getConnection("jdbc:h2:~/test", "sa", "");
        } catch (SQLException | ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
        return connection;
    }

    public static Controller getHomeController() {
        return new HomeController();
    }

    public static Controller getLoginController() {
        return new LoginController();
    }

    public static Controller getErrorController (){return new ErrorController();}

    public static Controller getRegistrationController(UserService userService) {
        return new RegistrationController(userService);
    }

    public static Controller getUserGetByIdController (UserService userService){
        return new UserGetByIdController(userService);
    }

    public static Controller getAllUsersController(UserService userService) {
        return new GetAllUsersController(userService);
    }

    public static Controller getRemoveController (UserService userService){
        return new RemoveController (userService);
    }

    public static Controller getUserFormController (){return new UserFormController();}

    public static Controller getUpdateController (UserService userService){
        return new UpdateController(userService);
    }

    public static UserService getUserServiceImpl(UserDao userDao) {
        return new UserServiceImpl(userDao);
    }

    public static UserDao getUserDaoImpl(Connection connection) {
        return new UserDaoImpl(connection);
    }

    public static Controller getAllCategoriesController (CategoryService categoryService){
        return new GetAllCategoriesController(categoryService);
    }

    public static CategoryService getCategoryServiceImpl (CategoryDao categoryDao){
        return new CategoryServiceImpl(categoryDao);
    }
    public static CategoryDao getCategotyDaoImpl(Connection connection) {
        return new CategoryDaoImpl(connection);
    }
}

public class UserServiceImpl implements UserService {
    private final UserDao userDao;

    public UserServiceImpl(UserDao userDao) {
        this.userDao = userDao;
    }


    @Override
    public User save(User user) {
        return userDao.save(user);
    }

    @Override
    public List<User> getUsersByName(String username) {
        return userDao.getUsersByName(username);
    }

    @Override
    public User getById(int userId) {
        return userDao.getById(userId);
    }

    @Override
    public User remove (int userId){
        return userDao.remove(userId);
    }

    @Override
    public User update(int userId) {
        return userDao.update(userId);
    }

    @Override
    public List<User> getAllUsers(){
        return userDao.getAllUsers();
    }
}

public class MainServlet extends HttpServlet {

    private final Map<Request, Controller> controllerMap = new HashMap<>();

    public void init() throws ServletException {
        controllerMap.put(Request.create("GET", "/root/home"), Factory.getHomeController());
        controllerMap.put(Request.create("GET", "/root/login"), Factory.getLoginController());
        controllerMap.put(Request.create("GET", "/error"), Factory.getErrorController());
        controllerMap.put(Request.create("POST", "/root/login"), Factory.getRegistrationController(
                getUserServiceImpl(
                        getUserDaoImpl(
                                getConnection()))));
        controllerMap.put(Request.create("GET", "/root/users"), Factory.getAllUsersController(
                getUserServiceImpl(
                        getUserDaoImpl(
                                getConnection()))));
        controllerMap.put(Request.create("GET", "/root/users/remove"), Factory.getRemoveController(
                getUserServiceImpl(
                        getUserDaoImpl(
                                getConnection()))));
        controllerMap.put(Request.create("GET", "/root/user"), Factory.getUserGetByIdController(
                getUserServiceImpl(
                        getUserDaoImpl(
                                getConnection()))));
        controllerMap.put(Request.create("GET", "/root/userform"), Factory.getUserFormController());
        controllerMap.put(Request.create("POST", "/root/userform"), Factory.getUpdateController(
                getUserServiceImpl(
                        getUserDaoImpl(
                                getConnection()))));
        controllerMap.put(Request.create("GET", "/root/categories"),Factory.getAllCategoriesController(
                getCategoryServiceImpl(
                        getCategotyDaoImpl(
                                getConnection()))));
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        handleRequest(request, response);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        handleRequest(request, response);
    }

    private void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String uri = getUri(request.getRequestURI());
        Request req = new Request(request.getMethod(), uri, request.getParameterMap());
        try {
            Controller controller = controllerMap.get(req);
            if (controller == null) {
                throw new RuntimeException("Cannot handle " + req);
            }
            ViewModel viewModel = controller.process(req);
            if (viewModel.hasCookies()) {
                Map<String, String> newCookies = viewModel.getNewCookies();
                for (String cookieName : newCookies.keySet()) {
                    response.addCookie(new Cookie(cookieName, newCookies.get(cookieName)));
                }
            }
                forward(request, response, viewModel);
            } catch (Throwable t) {
            request.getRequestDispatcher("/WEB-INF/error.jsp").forward(request, response);
        }
    }

    private String getUri(String requestURI) {
        if(!requestURI.contains("?")) {
            return requestURI;
        }
        return requestURI.substring(0, requestURI.indexOf("?"));
    }

    private void forward(HttpServletRequest request, HttpServletResponse response, ViewModel viewModel) throws ServletException, IOException {
        RequestDispatcher dispatcher = request.getRequestDispatcher(getView(request, viewModel));
        setAttributes(request, viewModel);
        dispatcher.forward(request, response);
    }

    private void setAttributes(HttpServletRequest request, ViewModel viewModel) {
        for (String attr: viewModel.getAttributes().keySet()) {
            request.setAttribute(attr, viewModel.getAttribute(attr));
        }
    }

    private String getView(HttpServletRequest request, ViewModel viewModel) {
        return request.getContextPath() + viewModel.getView();
    }

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>

<html>
<head>
    <title>Users</title>
    <style>
        <%@include file="/bootstrap/css/bootstrap.min.css" %>
        <%@include file="/bootstrap/css/hello.css" %>
        <%@include file="header.jsp"%>
    </style>

</head>
<body>
<div class="container">
    <h3>Users List</h3>

    <form method="post" action="/root/users" class="well">

    <table class="table table-striped">
        <thead>
        <tr>
            <td><b>UserId</b></td>
            <td><b>Username</b></td>
            <td><b>Email</b></td>
            <td><b>Action</b></td>
            <td><b>Action</b></td>
            <td><b>Action</b></td>
        </tr>
        </thead>
                  <c:forEach var = "user" items="${users}">
            <tr>
                <td>${user.userId}</td>
                <td>${user.username}</td>
                <td>${user.email}</td>
                <td><a href="/root/user?userId=${user.userId}" methods="get">User details</a></td>
                <td><a href="/root/users/remove?userId=${user.userId}" methods="get">Delete</a></td>
                <td><a href="/root/userform?userId=${user.userId}" methods="get">Update</a></td>
            </tr>
                  </c:forEach>
    </table>

    </form>
    <a href="/root/home" class="btn btn-lg btn-default">Home</a>
</div>
<script>window.jQuery || document.write('<script src="<c:url value="/bootstrap/js/jquery.min.js"/>"><\/script>')</script>
<script>
    <%@include file="/bootstrap/js/bootstrap.min.js" %>
    <%@include file="footer.jsp"%>
</script>

</body>
</html>

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>

<!DOCTYPE html>
<html lang="en">
<html>
<head>
    <title>User form</title>
    <style>
        <%@include file="/bootstrap/css/bootstrap.min.css" %>
        <%@include file="/bootstrap/css/hello.css" %>
        <%@include file="header.jsp"%>
    </style>
</head>
<body>

<div class="container">
    <form class="form-user" action="/root/userform?userId=${user.userId}" method="post">
        <h2 class="form-user-heading">Please input user's details</h2>

        <label for="inputUserId" class="sr-only">UserId</label>
        <input type="text" id="inputUserId" class="form-control" name="userId" placeholder=${user.userId}>

        <label for="inputUsername" class="sr-only">Username</label>
        <input type="text" id="inputUsername" class="form-control" name="username" placeholder="Username">

        <label for="inputPassword" class="sr-only">Password</label>
        <input type="password" id="inputPassword" class="form-control" name="password" placeholder="Password">

        <label for="inputEmail" class="sr-only">Email address</label>
        <input type="email" id="inputEmail" class="form-control" name="email" placeholder="Email">

        <button class="btn btn-lg btn-primary btn-block" type="submit">Update</button>
    </form>
    <a href="/root/users" class="btn btn-lg btn-default">Users list</a>
    <a href="/root/home" class="btn btn-lg btn-default">Home</a>
</div>
<script>window.jQuery || document.write('<script src="<c:url value="/bootstrap/js/jquery.min.js"/>"><\/script>')</script>
<script>
    <%@include file="/bootstrap/js/bootstrap.min.js" %>
    <%@include file="footer.jsp"%>
</script>
</body>
</html>

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">

    <title>Confirm registration page</title>

    <style>
        <%@include file="/bootstrap/css/bootstrap.min.css" %>
        <%@include file="/bootstrap/css/signin.css" %>
    </style>
</head>

<body>
<div style="text-align: center">
    <h1>Congratulations, your operation with <c:out value="${user.username}"/> is done successfully!</h1>
    <a href="/root/home" class="btn btn-lg btn-default">Home</a>
</div>

</body>
</html>