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Editorial Team
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Asked: 2026-06-09T14:24:33+00:00

I have a jsp page (says , MyJspPage.jsp ) – <html> <head> <meta http-equiv=Content-Type

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I have a jsp page (says , MyJspPage.jsp) – 

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<%
    ArrayList<Person> ownerList = (ArrayList<Person>) request
            .getAttribute("ownerList");
    //set again ..
        request.setAttribute("ownerList",ownerList) ;   

%>
</head>
<body>
        <%
            //itr on all the persons ..;
            for (Person person : ownerList) {
        %>
                    // some HTML code.. 
        <%
            }
        %>
            <form action="servlet123" method="POST">
                   // some fields .. 
                   <input type="submit" value="join" />
    </form>

</body>
</html>

And a servlet – 

@WebServlet("/servlet123")
public class servlet123 extends HttpServlet {
    private static final long serialVersionUID = 1L;


    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        // get the then set .. 
             ArrayList<Person> ownerList = (ArrayList<Person)request.getAttribute("ownerList"); 
        request.setAttribute("ownerList", ownerList);
             // forward to `MyJspPage.jsp`
            dispather.forward(request, response);
        }

}

Firstly another servlet forward to MyJspPage.jsp and it work fine , then there is like ping pong between MyJspPage.jsp and servlet123 . The problem is that when at the 2nd time reachs to MyJspPage.jsp it throws an exception – 

type Exception report

message java.lang.NullPointerException

description The server encountered an internal error (java.lang.NullPointerException) that prevented it from fulfilling this request.

exception 

org.apache.jasper.JasperException: java.lang.NullPointerException
    org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:549)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

It should be noted that when I omit the for loop from MyJspPage.jsp and change it to be – 

   <html>
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
    <%
        ArrayList<Person> ownerList = (ArrayList<Person>) request
                .getAttribute("ownerList");
        //set again ..
            request.setAttribute("ownerList",ownerList) ;   

    %>
    </head>
    <body>
                <form action="servlet123" method="POST">
                       // some fields .. 
                       <input type="submit" value="join" />
        </form>

    </body>
    </html>

all the relation between MyJspPage.jsp and servlet123 returns work fine .

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1 Answer

  1. Editorial Team

    This is one approach.

    JSP Code is as follows

    Instead of setting the arraylist again in the request, you can set it in session as follows
    session.setAttribute("ownerList",ownerList) ;

    You can check for the arraylist to be NOT null before using it in the for loop.

            if (ownerList != null)
        {
          for (Person person : ownerList) {
    %>
                // some HTML code.. 
    <%
          }
        }
    %>

    In the servlet you can write the code as

     HttpSession session = request.getSession(false);
 ArrayList<Person> ownerList = (ArrayList<Person)session.getAttribute("ownerList"); 
 request.setAttribute("ownerList", ownerList);
 session.setAttribute("ownerList", null); // toremove unnecessary code from the session

    There could be other approach also. This one is just closer to the one you chose.

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