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From "Carlos Ferreira" <carlos.ferre...@gilem.com>
Subject Re: ??? Using JSPs to Send Not-Modified-Since Header ???
Date Tue, 04 Jun 2002 15:33:56 GMT

a not so good solution would be to subclass
org.apache.jasper.runtime.HttpJspBase ( or redesign it ) with your
required behaviour and extend your jsp pages from this new class.
the problem is that HttpJspBase is tomcat specific. perhaps somebody has a
better idea.

Carlos Ferreira
Gilem Informatique

> Hi all,
>
> In looking at past posts, I'm afraid I know the horrible answer
> to this issue but I thought I'd ask just in case I missed
> anything.
>
> Let me start by saying I'm using Tomcat v4.0.4 beta 3.
>
> As you know, when a client (usually a web browser) has a cached
> version of a resource (usually a web page) it can send an
> "If-Modified-Since" header to the HTTP server. The server
> compares the time/date stamp specified in the header with that of
> the requested resource. If the resource has *not* been modified
> since the time specified in the "If-Modified-Since" header, the
> server sends back a 304 (Not-Modified) response, effectively
> telling the client (usually a web browser) that its cached
> version of the resource is still valid.
>
> When writing a servlet, it's easy to handle this sort of
> scenario. The javax.servlet.http.HttpServlet class has a
> "service()" method. This method first checks if the incoming HTTP
> method is a GET. If it is, the "service()" method proceeds to
> call the "getLastModified()" method of the servlet. As a
> developer, you can override "getLastModified()" to return a long
> value representing the last time the requested resource was
> changed. Depending on the value returned by "getLastModified()"
> (note that -1 is returned if you don't override the method) the
> "service()" method may simply return a 304, Not-Modified response
> rather than calling the servlet's "doGet()" method.
>
> Now, the $18.32 Question: How do you ensure "getLastModified()"
> is called in JSP?
>
> No, you cannot simply do this:
>
> <%!
>   public long getLastModified() {
>      return xxx;
>   }
> %>
>
> The problem is that the above method will never be called by the
> container.
>
> I traced through some of the Tomcat/Catalina/Jasper code and it
> seems to me that the response code is being set to 200/OK very
> early on in the processing.
>
> I also took a cursory look at the JSP spec and didn't find any
> indication of setting a "Not-Modified" response code...so, I am
> thinking this is something that is (strangely) missing in the JSP
> specification. I have a JSP page that needs to update itself once
> per day. Therefore, it would be very handy to have the
> "getLastModified()" functionality enjoyed by servlet writers.
>
> Can anyone confirm this?
>
> Thanks...
>
>
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