PID, thanks for your insight.
Two comments about that:
1) I agree with you for includes and forwards, but for errors? I would have thought that
the definition of "error" is that something went wrong, and Tomcat should start
from scratch and just render the error page. I didn't think of it as really a forward...
2) So you are suggesting that writing out to the response.getOutputStream() as
I go is wrong? Instead, I need to:
a. buffer my output locally
b. once I am sure that it can all be created correctly, *then* I write out the
buffer to the response?
Am I understanding you correctly?
Thanks,
--
Dave Cherkassky
VP of Software Development
DJiNN Software Inc.
416.504.1354
Pid wrote:
Dave Cherkassky wrote:
A long question:
First, I have a Servlet that writes to response.getOutputStream().
Here's a snippet:
public class AuditTrailServlet extends HttpServlet {
public void doGet( HttpServletRequest request, HttpServletResponse
response )
response.setContentType( "application/vnd.ms-excel" );
response.setHeader( "Content-Disposition", "attachment; filename="
+ fileName );
ResultSet rs = ...;
for ( int row = 0 ; rs.next(); row++ ) {
// iterate over each row in the ResultSet
for( int col = 0; fieldNameIt.hasNext(); col++ ) {
// iterate over each column in the results, write to spreadsheet
// custom code.
// let us assume this block has a bug that occasionally throws
a NullPointerException, // but only after a bunch of cells are
written first.
response.getOutputStream().write( /* excel byte[] */ );
// more custom code.
}
}
rs.close();
response.setStatus( HttpServletResponse.SC_OK );
}
}
Second, I have the following in the web.xml file, to tell tomcat to use
a custom error page:
<error-page>
<exception-type>java.lang.Throwable</exception-type>
<location>/myError.jsp</location>
</error-page>
Last, here's myError.jsp:
<%@ page isErrorPage='true' %>
<html>
<body>
<h1>System Error</h1>
<p>
You have encountered a system error.
</p>
<%-- custom error processing that can't be done in a static .html page
--%>
</body>
</html>
So, it all seems standard and straight-forward, right?
However, instead of seeing a nice custom error page when the NPE
happens, I get the "ugly" Tomcat error page, and
the following in the Tomcat logs:
java.lang.IllegalStateException: getOutputStream() has already been
called for this response
at
org.apache.catalina.connector.ResponseBase.getWriter(ResponseBase.java:709)
at
org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:127)
at org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:128)
at
org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:121)
at
org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java:137)
at
org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:153)
at
org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:148)
at org.apache.jsp.error_jsp._jspService(error_jsp.java:284)
Yes, I know -- I *am* using Tomcat 4.1 (rather than the latest and
greatest) for various legacy and political reasons.
But my question is this:
- Is this a known bug? Or am I doing something wrong with either the
servlet, the web.xml or with the jsp page?
I'm not sure it's a bug; logically, if you've sent a chunk of the
response (and therefore committed the response, sent headers etc)
*before* an exception happens how is Tomcat then supposed to tell the
client to stop and then display a different page?
p
Thanks,
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