Hello everybody,
As I found a solution to my problem, I thought I would share it in case
someone else comes up against the same issue. The reason for the client
not acting on the redirect is that sendRedirect does not send any
Content-length header, and the client will then wait for an eventual
Content body until the servlet finishes. This could be avoided if the
sendRedirect would include "Content-length: 0" in its HTTP headers. I
solved my problem by manually constructing the redirect on the
HttpServletResponse object ('out' below).
Old code:
final int PARTIAL_HITS = 25;
for (int i = 0; i < hits.length(); i++) {
/** Insert into table omitted */
if (i == PARTIAL_HITS) {
// Intermittant redirect, not acted on until doPost returns
out.sendRedirect(resultUrl);
}
}
if (!out.isCommitted()) {
// Final redirect
out.sendRedirect(resultUrl);
}
New code:
final int PARTIAL_HITS = 25;
for (int i = 0; i < hits.length(); i++) {
/** Insert into table omitted */
if (i == PARTIAL_HITS) {
// Intermittant redirect, acted on immediately
out.setHeader("Location", resultUrl);
out.setStatus(303);
out.setContentLength(0);
out.flushBuffer();
}
}
if (!out.isCommitted()) {
// Final redirect (if case less than PARTIAL_HITS found)
out.sendRedirect(resultUrl);
}
> Hello again,
>
> Thanks for the response, but it seems like my phrasing was a bit unclear.
> The problem is not the second redirect - in fact there will be no
> multiple redirects. The second redirect is only there for the case when
> less than 25 hits are found and the first redirect is not called. The if
> clause will prevent the program for trying to redirect twice.
>
> My problem is rather that the redirect is only commited - the response
> is sent to the client - until the doPost method/thread finishes. I
> expected to be able to redirect (once) in the middle of the loop. What I
> am trying to accomplish is to do a query, enter the hits into a
> temporary table, and redirect to another program that displays a paged
> list of hits by reading from the table - in effect using the table as a
> queue. Since the paged display only shows the top 25 hits, there is no
> need to wait for all the query results.
>
> So once more, my problem is that the redirect is not committed until the
> function returns. Any help much appreciated.
>
> Tore
>
> Alan Chaney wrote:
> > Tore
> >
> > Your code below is written as though the 'out' was like writing data to
> > a console. The processing in a servlet is part of a request/response
> > cycle, where the 'request' tells it what to do and the response is the
> > reply.
> >
> > Because of the nature of the request/response cycle you only get one
> > chance at the reply. The javadocs for HttpServletResponse.sendRedirect
> > make this clear.
> >
> > "If the response has already been committed, this method throws an
> > IllegalStateException. After using this method the response should be
> > considered to be committed and should not be written to."
> >
> > In other words, in one servlet request/response cycle you get exactly
> > one chance to issue a 'sendRedirect'. If you think this through you'll
> > see that this is how it has to be:
> >
> > Browser sends request to servlet
> > Servlet process request and sendsRedirect
> > Browser display response.
> >
> > Your problem is that you are trying to generate a second response
> > without a correspondng request. The first response is for the 'top 25'
> > and the second is for 'all the rest', but by then you've already
> > committed the response.
> >
> > To achieve what I think you are trying to achieve would require you to
> > create some mechanism where the lucene query results are processed in a
> > separate thread and your application makes TWO requests - one for the
> > first set of results and then one for the final set of results.
> >
> > There are far too many different ways to do this to detail here - I hope
> > this helps
> >
> > Regards
> >
> > Alan Chaney
> >
> >
> >
> > Tore Eriksson wrote:
> > > Hi everybody,
> > >
> > > I have a problem with redirects in Tomcat 5.5.25. I am doing a Lucene
> > > search and would like to send a redirect after finding the top 25 hits,
> > > commit this response, and then continue processing the remaining hits.
> > > The relevant parts of the doPost() code are as below:
> > >
> > > final int PARTIAL_HITS = 25;
> > >
> > > for (int i = 0; i < hits.length(); i++) {
> > >
> > > Document doc = hits.doc(i);
> > > String citation = doc.get("citation");
> > >
> > > /** Insert into table */
> > > try {
> > > insertId.setInt(1, java.lang.Integer.parseInt(citation));
> > > insertId.executeUpdate();
> > > }
> > > catch (SQLException e) {
> > > out.sendError(500, "Bad SQL insert: " + e);
> > > }
> > > catch (Exception e) {}
> > >
> > > if (i == PARTIAL_HITS) {
> > > // Intermittant redirect
> > > out.sendRedirect(resultUrl);
> > > }
> > > }
> > >
> > > insertId.close();
> > >
> > > if (!out.isCommitted()) {
> > > // Final redirect
> > > out.sendRedirect(resultUrl);
> > > }
> > >
> > > My problem is that the intermittant redirect is not committed until the
> > > function returns, which will take quite some time for some queries. I
> > > have tried HttpServletResponse.flushBuffer() and other possible
> > > variations. Any pointers would be most appreciated.
> > >
> > > Tore
>
>
> _______________________________________________________________
> Tore Eriksson [tore.eriksson ad po.rd.taisho.co.jp]
_______________________________________________________________
Tore Eriksson [tore.eriksson at po.rd.taisho.co.jp]
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