Re: [OT] Servlet process issue

[Erik Price <ep...@ptc.com>]

Tam, Michael wrote:
> Hi all,
> 
> Sorry for the [OT].  Since many of you are the experts on servlet
> technology, I'd like to ask for suggestions or comments on the servlet
> process I am working on.
> 
> Process:
> 1)  I have a form html (A) to upload data files through an UploadServlet (B)
> which stores the files in the file system.
> 2) Then (B) will forward the request to ValidationServlet (C) which reads
> the files for validation and generates log file.
> 3) Then (C) will forward the request to LoadServlet (D) which use the log
> file to load the clean data to DB.

A servlet is a highly specialized kind of object that is specifically 
designed to receive, process, and respond to requests.  In the case of 
HttpServlets, this would be HTTP requests.

It seems that unless your ValidationServlet and LoadServlet are ever 
going to be directly accessed with HTTP requests, they're probably 
better off being written as regular Java classes (like Validator and 
Loader).  I do not know anything about the overhead incurred by making 
them servlets, but it just seems that by subclassing HttpServlet for 
these objects, at least for the use case you've described, you're 
inheriting a lot more functionality than you'd ever need.

This will also simplify the design question you're asking -- you don't 
have to "backtrack" anywhere, your UploadServlet can just do whatever it 
is you want to be done when the request processing is finished (dispatch 
to a JSP saying "thank you"?).

Note that when your HTTP request is sent to UploadServlet, UploadServlet 
/is/ a new thread, so the user should not be able to interfere with this 
process.  If the user tries clicking "Submit" again, a totally new 
UploadServlet will respond.  If you wish to disable this ability, there 
is a technique involving the setting of a flag in the user's session 
that prevents any further requests being received until the processing 
is done.  But you have to implement this yourself.  The whole technique 
is detailed at 
<http://developer.java.sun.com/developer/EJTechTips/2003/tt0114.html#2>


HTH,

Erik


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