Java - 检查If Else语句是否赋值

Question

尝试编写一些代码来检查是否已在JSP中的表单中输入了某些内容,如果没有,则为其分配会话中的值.

完成此操作后,将从所有参数中创建一个对象.

写了所有代码但是

User user = new User(username, firstname, surname, password); comes up with a cannot **find symbol error** 

我意识到这是因为它不在任何ifs中.有人会告诉我如何更改代码以便它可以使用这些值吗？

代码:

  try {
                    User sessionuser =(User)session.getAttribute("User");
                    String username = sessionuser.getUsername();

                    if (request.getParameter("firstname").equals (null)){
                        String firstname = sessionuser.getFirstname();
                    }
                    else{String firstname = request.getParameter("firstname");
                    }

                    if (request.getParameter("surname").equals (null)){
                        String surname = sessionuser.getSurname();
                    }
                    else{String surname = request.getParameter("surname");
                    }
                    String password = request.getParameter("password");

                    User user = new User(username, firstname, surname, password);
                    //this.updateUser(user); 
                    this.updateUser(username, firstname, surname, password);

                    //user.updateUser();

                    session.setAttribute("User", user);
                    request.setAttribute("u", user);
                    request.getRequestDispatcher("UpdateUser.jsp").forward(request,     response);

Answer 1

快速提示

if (request.getParameter("firstname").equals (null)){ 

...

if (request.getParameter("surname").equals (null)){

...

这永远不会是真的,它可能是false或抛出NullPointerException.用==而不是equals()