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Web Component Certification (OCEJWCD)

Request Attribute confusion

Joe San

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posted 17 years ago

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Guys,

I tried the following,

My test.jsp,

But if I comment Line 1, I'm getting a null pointer?? I know the request.getAttribute("jothi") in the System.out.println(request.getAttribute("jothi")) gets a call to toString90 method but why the other throws a null pointer??

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Srinivasan thoyyeti

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posted 17 years ago

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Hi Jyothi,

When you first request the jsp file

1. jsp converted to servlet and in service attribute jyothi placed.
2. and in response html form sent.
3. your request ends here.(that means your request,response objects gone).

secondly when user submits the form

1. control reaches servlet
2. tries to find jyothi in request scope.
finally gives up return null.

[ May 11, 2007: Message edited by: Srinivasan thoyyeti ]

Thanks & Regards, T.Srinivasan
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Christophe Verré

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posted 17 years ago

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Try the following :

You are using a java1.5 feature called unboxing, which converts an Integer into an int.
But you are trying to convert null into an int, which fails.
It would work with Integer i = (Integer)request.getAttribute("jothi");

Maybe you'd better use SDK1.4 to practice for this exam.

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Joe San

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posted 17 years ago

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Satou,

You are really amazing. No words to praise you man. You point out my mistakes elegantly. Thanks!

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Joe San

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posted 17 years ago

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Consider the code as below,

My test.jsp file,
 
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>SCWCD Examples</title>
</head>
<body>
<form action="ExampleServlet">
<% request.setAttribute("jothi", new Integer(1)); %>
<input type="submit" value="Submit">
</form>
</body>
</html>
 
The servlet,
 
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    request.setAttribute("shan", "shan");
   RequestDispatcher view = getServletContext().getRequestDispatcher("/includedjsp.jsp");
   view.forward(request, response);
} 
 
The includedjsp.jsp file,
 
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>I'm getting inserted</title>
</head>
<body>
<% request.setAttribute("shan", "shanar"); %>
<jsp:forward page="test1.jsp" />
</body>
</html>
 
The test1.jsp,
 
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>I'm the lead</title>
</head>
<body>
<h1>I'm being written here</h1>
<%
   out.println(request.getAttribute("shan"));
%>
</body>
</html>

I'm confused as when I run this I'm getting shanar as the o/p. Shouldn't the forward call in includedjsp.jsp ignore anything that we set???

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