Here's my attempt at helping.....
It's a serialization issue. The jrun serializes your objects which are in
sessions when jrun shutsdown, and tries to "unserialize" them to reinstantiate
them when it starts back up. If you don't specify a serialVersionUID in your
changed class, as described below, then java's serialization mechanism makes
it's own SHA fingerprint for the class that it stores when serializing an
object. When a class changes and an attempt is made to unserialize an older
version of the class, the SHA fingerprint is different and it won't read in
objects with different fingerprints. The way to indicate that your new class is
compatible with the old (if of course it is) is to obtain the fingerprint of the
earlier version of the class using the serialver program that is a part of the
JDK to obtain the number.
>serialver yourpackage.YourClass
outputs:
yourpackage.YourClass: static final long serialVersionUID =
_____________________L;
You then put that line all later versions of your class. This will cause the
serialization mechanism to not compute the fingerprint manually but instead use
that value.
This is my paraphrase of information from Horstman and Cay's CoreJava book.
Hope it helps you.
Lynn
Sid wrote:
> I'm running windows2000 and JRun 3.0
>
> My servlet:
> 1) Creates & populates an instance of my class called JournalEntry.
> 2) puts it into the session,
> 3) passes control to a JSP page for rendering
>
> Everything works fine, the class is passed to the JSP, and is displayed
> properly.
>
> However, when I recompile the servlet, with the JRun server still running,
> all subsequent requests throw an exception.
> This applies to both existing and new sessions. I must restart the jrun
> server for it to work again.
>
> Thanks for any expert assistance!
> Supporting info is below...
> ============
>
> This is the error from the log...
>
> 03/20 08:45:00 info (JRun) journal.JournalMenu: init
> 03/20 08:45:07 info (JRun) jrun__journalentry2ejsp11: init
> 03/20 08:49:05 info (JRun) journal.JournalMenu: destroy
> 03/20 08:49:05 info (session) Class change detected - reloading all session
> data
> 03/20 08:49:05 info (session) 3 session(s) persisted
> 03/20 08:49:05 info (session) Recovering 3 session(s)
> 03/20 08:49:05 info (JRun) journal.JournalMenu: init
> 03/20 08:49:07 error (JRun) Couldnt pass to journalentry.jsp
> [java.lang.ClassCastException: journal.JournalEntry]
> java.lang.ClassCastException: journal.JournalEntry
> at jrun__journalentry2ejsp11._jspService(jrun__journalentry2ejsp11.java:39)
> at allaire.jrun.jsp.HttpJSPServlet.service(../jsp/HttpJSPServlet.java:40)
> at allaire.jrun.servlet.JRunSE.service(../servlet/JRunSE.java:1013)
> at allaire.jrun.servlet.JRunSE.runServlet(../servlet/JRunSE.java:925)
> at
> allaire.jrun.servlet.JRunNamedDispatcher.forward(../servlet/JRunNamedDispatc
> her.java:34)
> at allaire.jrun.jsp.JSPServlet.service(../jsp/JSPServlet.java:175)
>
> Relevant code snippets below:
> ============================
> Servlet:
>
> JournalEntry je = getJournalEntry(requestedId);
> HttpSession session = req.getSession();
> session.setAttribute("journalentry", je);
> ServletContext sc = this.getServletContext();
> RequestDispatcher rd = sc.getRequestDispatcher("/journalentry.jsp");
> if (rd != null) {
> try {
> rd.forward(req,res);
> } catch (Exception e) {
> sc.log("Couldnt pass to journalentry.jsp", e);
> }
> }
>
> JSP:
>
> <%
> journal.JournalEntry je =
> (journal.JournalEntry)session.getAttribute("journalentry");
> URL url = je.getUrl();
> %>
> .....
> <TR ALIGN="left" VALIGN=middle">
> <TD WIDTH="10%">ID</TD>
> <TD><%=je.getId()%></TD>
> </TR>
>
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