web service client reference, in a servlet

Question

I have a servlet, and that servlet uses a .net web service to perform some function. To do this, I created the webservice client in Netbeans using the "jax-rpc" style client.

Let's say that my service name is "Tester". Then two of the generated classes are called "Tester", and "TesterSoap".

To get a reference to the web service, I need to do this:

Tester t = new Tester_Impl();
TesterSoap tsoap = t.getTesterSoap();

To use the webservice, I can then do this:

tsoap.runTest();

My question is, since this is a servlet which gets executed many times, should I store the first two lines in static variables (so they only ever get executed once), or store them locally so that they execute everytime the servlet is executed?

Another way of asking the same question: is there a performance hit everytime the first two lines are called? (I'm testing everything locally so it's hard to measure).

Thanks...

Answer 1

If the default constructor and any of the initialization blocks of the Tester_Impl() class and the method getTesterSoap() doesn't do anything expensive (e.g. reading file from disk, loading data from DB, connecting a socket, etc, I however suppose it doesn't) then you don't need to worry about it.

You can consider declaring them as an instance variable of the class extending from HttpServlet. But, a big but, it is going to be shared among all HTTP requests, because there will be only one instance of the particular servlet class during whole application's lifetime. So if the Tester_Impl class is supposed to have a state, then it is a very bad idea to declare it as an instance variable. It would then be shared among all requests. With other words, it's not threadsafe. If you want to ensure threadsafety in servlets, then declare everything in the very same method block.

Answer 2

I would not optimize prematurely here. Test this out in as close to a production environment as you can (i. e. not on your local box) and see what the performance hit is. What I've done in the past is write a small shell script that hits my server with wget n times with a delay of k milliseconds and then measured the latency, possibly instrumenting the code with some timing or profiling myself (or with jvisualvm or some other profiling tool).

If you want to protect your design from a possible performance hit without doing the testing, you could use a factory to provide instances of the service client and then you could swap out singleton service clients for many of them whenever you feel like it.