java.lang.NullPointerException in servlet error 500 - servlets

Question

When I run my Servlet I get this error:
java.lang.NullPointerException please i tried many solutions but it didn't work it's simple code
public LoginServlett() {
super();
}
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String name = request.getParameter("UserName");
String pass = request.getParameter("Password");
RequestDispatcher d=null;
if (name.contentEquals("Gestionnaire") && pass.contentEquals("1234")) {
HttpSession session;
session =request.getSession(true );
d =request.getRequestDispatcher("/EspaceGestionnaire.html");
session. setAttribute("NomSauvegardé" ,name);
}
else {
d = request.getRequestDispatcher("/Authentification.html");
d.forward(request, response);
}
}
protected void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {
}
}

Answer 1

A NPE will be thrown from the code if the Username and Password parameters are not set. If they are not set then the user and pass variables will be null, and when the contentEquals methods are called on them a NPE will be thrown as a result.
A way to do this would be to reverse the equality checks so the operation is called on string you want to check:
if ("Gestionnaire".contentEquals(name) && "1234".contentEquals(pass)) {
which will do what your code intends without throwing a NPE.
Although if you are sending passwords over the internet it is better to use POST than GET. For Java EE security there is also the new security API (https://javaee.github.io/security-spec/)