RVASUDEV wrote:
> Hi servlet gurus,
>
> Env:
> HP-UX 10.20, Java 1.17, JSDK 2.1
>
> There's a small servlet I've written, that calls the UNIX "uptime" and "w"
> commands using a Process object, reads their output and displays it
> back to the user. It gives the error shown below at the printW() method
> (blank/irrelevant lines deleted from program and output). You have
> to run the servlet, check the w checkbox, then click the submit button
> to generate the error. Any ideas ? There is no indication of which
> line the error is occurring on, though an earlier bug (also a NPE) was fixed
> after seeing the line no. in the error msg.
>
Suggestions:
* Compile your servlet without optimization, and turn off the JIT at run time
so that line numbers will be included in the traceback.
* Execute this under a debugger, or add a whole bunch more
debugging print statements inside the printW() method.
Debugging servlets is no different than debugging any other program -- you've
got to narrow down where your problems are occurring.
However, even after you fix this particular bug, you will soon find out that
this servlet will fail horribly when two or more people try to use it at the
same time. This is caused by the fact that you are using instance variables
(like srvOut, prcOut, and so on) instead of method variables and/or arguments.
There is only one copy of these variables, so simultaneous access on multiple
threads is going to scribble on them.
>
> TIA
> Vasudev
>
Craig McClanahan
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