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+---- Thread: [Java] how to handle nullPointerException on JSP (/showthread.php?tid=4889410)
how to handle nullPointerException on JSP - SunnyAkuma - Jul 1, 2015
this is my JSP , it'll get the username and email using session.getAttribute("key") method.
The problem is, If someone tries to open this page directly , without logging in , Then the values of the variable username and email should be null , and the user should be redirected to another page.
But instead I'm getting a nullPointerExcepetion just as I try to run this page without beginning the session , aka , going directly to this page without logging in using the url.
Here's the code.
Code
<%@page import="supportServlets.MyBeans"%>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>JSP Page</title>
</head>
<body bgcolor='#c1c1c1'>
<%
HttpSession studentSession=request.getSession(false);
String username=(String)studentSession.getAttribute("username");
String email=(String)studentSession.getAttribute("email");
if(username.equals(null)||email.equals(null))
{
MyBeans.setFlag("no");
response.sendRedirect("studentLogin.jsp");
}
%>
<jsp:include page="headerLogo.jsp"/>
<form action="mainQuizPage">
<center>
<div style="width: 700px; background-color: whitesmoke">
<center>
<h2>Welcome <%=username%></h2>
<br>
</center>
</div>
</center>
</form>
<jsp:include page="footerLogo.jsp"/>
</body>
</html>* - JavaProphet - Jul 1, 2015
A simple solution is to do a check for a null, then return an error to the user.
* - JavaProfit - Jul 1, 2015
(Jul 1, 2015 07:13 PM)JavaProphet Wrote: A simple solution is to do a check for a null, then return an error to the user.
To extend off of this, you never want to catch a NullPointerException. So unit test your code before your server goes live to make sure anything that might cause an NPE is fixed (usually the if(obj != null) check is applied here).
* - SunnyAkuma - Jul 3, 2015
well, it's simple , I didn't think of it before. You can't check if a String is null using .equals() method.
Because,
String a;
Here 'a' is an object of class String that contains method named equals().
now if a = null
then you can't call a.equals(null);
because that will be like ---> null.equals(null);
* - JavaProfit - Jul 3, 2015
(Jul 3, 2015 12:04 PM)SunnyAkuma Wrote: well, it's simple , I didn't think of it before. You can't check if a String is null using .equals() method.
Because,
String a;
Here 'a' is an object of class String that contains method named equals().
now if a = null
then you can't call a.equals(null);
because that will be like ---> null.equals(null);
No just use == for null checks. You can't invoke a non-static method off of a null object.
* - SunnyAkuma - Jul 5, 2015
(Jul 3, 2015 01:46 PM)Systemic Wrote: No just use == for null checks. You can't invoke a non-static method off of a null object.
Did you even read my comment ?
* - JavaProfit - Jul 5, 2015
(Jul 5, 2015 12:37 PM)SunnyAkuma Wrote: Did you even read my comment ?
Yes and you blabbered on about something that could be written in 1 sentence.