How do I get user id in a session?

Question

I am doing a project using jsp and Servlet, I need that when a user logs in, his id is saved in the session, so that with this id, the system knows that this id user is making changes to his data (example, phone change). How could I do that?

Control:

public void login(HttpServletRequest request, HttpServletResponse response) throws IOException, ClassNotFoundException, SQLException, ServletException{
    String login = request.getParameter("usuario");
    String senha = request.getParameter("senha");

    Usuario usuario = new Usuario();
    usuario.setEmail(login);
    usuario.setSenha(senha);

    UsuarioDAO usuarioDAO = new UsuarioDAO();
    Usuario usuarioAutenticado = usuarioDAO.validar(usuario);

    if (usuarioAutenticado !=null){
        HttpSession sessaoUsuario = request.getSession();
        sessaoUsuario.setAttribute("usuario",usuarioAutenticado);
        sessaoUsuario.setMaxInactiveInterval(10);
        response.sendRedirect("home.html");
    }else{
        response.sendRedirect("erroLogin.html");
    }
}

DAO:

public Usuario validar(Usuario usuario) throws ClassNotFoundException, SQLException{

    Connection con = FabricaConexao.getConexao();

    Usuario us= null;

    PreparedStatement comando = con.prepareStatement("select * from usuario where email = ? and senha=?");
    comando.setString(1,usuario.getEmail());
    comando.setString(2,usuario.getSenha());

    ResultSet resultado = comando.executeQuery();

    if (resultado.next()){
        us=new Usuario();
        us.setEmail(resultado.getString("email"));
        us.setSenha(resultado.getString("senha"));
        //us.setPerfilAcesso(resultado.getString("perfil_acesso"));

    }

    con.close();
    return us;
}

HTML:

<form role="form" action="login" method="POST" >
            <label for="usuario">Usuario (e-mail): </label><br>
            <input type="text" name="usuario" id=usuario required><br>
            <label for="senha">Senha </label><br>
            <input type="password" name="senha" id=senha required><br>

            <br><input type="submit" class="btn btn-login" value="Login">
            <br><a href=cadastroConta.html>Nao possui conta? Click aqui</a>
        </form>

Answer 1

Celina, you already have the user ID saved in the session.

You see, when you put:

sessaoUsuario.setAttribute("usuario",usuarioAutenticado);

Hence, from this, you can recover the user ID at any time, either in Servlets or in JSP. You can do so:

Servlets

Usuario usuario = (Usuario)request.getAttribute("usuario");
Long id = usuario.getId(); //Aqui você ja tem o id do usuário

JSP (Using JSTL)

${sessionScope.usuario.id}

For security reasons, you can only post the ID, as @R.Santos suggested:

request.getSession().setAttribute("idUsuario", usuarioAutenticado.getId());

Since it is common for the user object to contain an attribute senha for example.

I hope I’ve helped.