Steve Dietrich wrote:
> Hi all,
>
> I have written a service servlet that other servlets can invoke to perform
> special functionality. I chose to write it as a GenericServlet and not just as
> a regular class so that I can use the log() feature to examine my jserv.log file
> in Apache (we all know how painful it is to debug run-time problems with
> servlets).... anyway, I use (from Hunter)
>
> MyServlet servlet = (MyServlet)getServletContext().getServlet("MyServlet");
>
> in the calling servlet to grab a handle to the service servlet, it compiles
> fine, but I get a run-time error ClassNotFoundException in Jserv.log.
> So, obviously I need to force the webserver to instantiate the service object
> prior to using getServlet.... HOW do I do this?
>
The issue is not instantiating the servlet before the call .. the getServlet()
method does that for you. A ClassNotFoundException indicates that the servlet
engine could not find your class file, which indicates a configuration error. Make
sure that the "MyServlet" class is available in the repositories you have
configured for your zone (in Apache JServ).
>
> I am still a novice with servlets... If there is a more appropriate way entirely
> different that this, please let me know!
>
> PS I am working under the assumption that once I get the handle to the service
> object that I can invoke it's methods and pass and return objects between the
> two.
>
This approach will work, but not for long. In the 2.1 servlet API, the
getServlet() call is deprecated and required to return NULL, which eliminates its
usefulness for providing access to shared services. This was done for many, many,
very good reasons -- despite the fact that it will break a *lot* of current
servlets when you upgrade to a 2.1-compliant servlet engine.
The assumption in your PS is correct, and that's the basis of the problem. For
example, nothing stops you from calling the destroy() method of the servlet you got
a reference to, after which your servlet thinks it has been shut down but the
servlet engine does not know that. Also, nothing stops you from calling the
service() method of a SingleThreadModel servlet from several threads yourself, even
though the servlet engine promises not to do that. This kind of thing is a recipie
for disaster.
In a 2.1 world, the ability to store arbitrary objects in your servlet context
(getServletContext.setAttribute()) is the best way to share service objects.
Alternatively, you can use the Singleton pattern and provide classes with static
factory methods that can be utilized even if you don't have a reference to a
particular instance.
>
> Steve Dietrich
> PG&E Energy Trading
>
Craig McClanahan
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