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Gerd,
On 3/9/13 8:39 AM, Gerd Zimmer wrote:
> I'm working on a WCMS system where I want to compile some view
> components at runtime. I found the Jasper howto to compile using
> Ant, but that's not what I need.
>
> I have dynamic JSP code stored in a database.
>
> Simplified I want to do something like this:
>
> protected void doRequest(HttpServletRequest request,
> HttpServletResponse response) throws ServletException, IOException
> {
>
> int templateId = request.getParameter("templateId"); String jspCode
> = db.queryString("select jspCode from templates where id =" +
> templateId); Jasper jcpc = new Jasper(); Servlet jspServlet =
> jspc.compile(jspCode) forward(jspServlet);
>
> }
>
> For sure this is very simplified. I know that the Jasper JSPC will
> need much more configuration/environment set.
>
> Can someone point me to the right classes to start?
Actually, I wonder if it might make more sense to write a a DirContext
that understands your database layout and so it can ignore requests to
things that aren't your db, provide caching (if appropriate), etc.
That way, you could have Tomcat handle the URL -> db-template mapping
for you. You might have to change the format of your URLs (from
/dynamic-jsp?templateId=foo to /dynamic-jsp/foo or something like
that) but it would simplify your code a lot.
I know that the whole resource-loading subsystem of Tomcat has been
recently changed drastically, so I'm not sure if there is a solution
that will work across Tomcat 6, Tomcat 7, and (eventually) Tomcat 8,
but the concept should be the same.
Invoking Jasper yourself isn't terribly easy, and once you compile,
you have to convince the JSP ClassLoader to load your new class...
that stuff isn't supposed to be controlled from the outside: it's all
supposed to be controlled by the JSP servlet. If you can make it look
like your JSP resources are on "the disk" (using the technique
outlined above), you can have the JSP servlet do all the dirty work
for you.
Good luck,
- -chris
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