Re: JSP: runtime errors...

From:

Lew <lew@nospam.lewscanon.com>

Newsgroups:

comp.lang.java.help

Date:

Sun, 08 Apr 2007 12:53:59 -0400

Message-ID:

<IeWdnRS9ZLG0g4TbnZ2dnUVZ_hqdnZ2d@comcast.com>

easynews_9103 wrote:

a little while ago I posted a question as to why somtimes I have the
problem with JSPs that they "drop" template code.. (print just first and
second div out of 20, etc..)

I was advised by Lew that I should define and error JSP for the app and
define it in web.xml.. I have now done this and still have no idea why
this JSP I'm working on sometimes stops generating template code in
"midstream.." I have followed instructions here,
http://java.sun.com/developer/EJTechTips/2003/tt0114.html#1, and thus
did, in web.xml:

  <error-page>
    <exception-type>java.lang.NullPointerException</exception-type>
    <location>/error.jsp</location>
  </error-page>

can you do a tag for each of the Exceptions under java.lang?

at any rate I added this tag:

   <error-page>
     <exception-type>java.lang.RuntimeException </exception-type>
      <location>/error.jsp</location>
  </error-page>

error page:

  <%@page isErrorPage="true" %>
  <html>
  <head>
  </head>
     An Application Error 1 has occurred.<br>
     The error class is <%=exception.getMessage();%>
  </body>
  </html>

still, my JSP is printing just two divs out of 15, and I get no info as
to why this is happening (divs generated in standard way inside a
loop..) the error page does not load..

I would appreciate some suggestions.. thank you...

Another diagnostic approach is to embed java.util.logger or org.apache.log4j
log calls in your code. (Apache commons-logging is a nice wrapper for both.)

If you are using an MVC architecture you can embed the logger calls in your
Java code. If not, you might have to use scriptlet to embed them in your JSPs.

Sometimes I have had to specify in the non-error JSP where its error page is.
I don't know why. It might've been an artifact of my development environment.

logger calls are great - you get a permanent record of where things happen and
where they go wrong, if you design your log calls intelligently.

A third approach is to run the app from within a debugger. Both Eclipse and
Netbeans, just to name two, excel at this. Trace the JSPs as they write to
the client, step by step. When it blows up you've found your problem.

--
Lew

--
Lew