Is there any particular reason you can't add this logic to the
existing "processRequest" method? I'm all for aspects ;), but I also
believe in doing the "simplest thing that can possibly work". I may
not really understand your requirement, however.
Assuming an aspect is the correct approach, here's an untested
skeleton aspect that should do what you want:
after(HttpServletRequest request, HttpServletResponse response):
execution (* MyServlet.processRequest(request, response)) &&
args(request, response) {
String p = (String)request.getParameter("p");
request.setAttribute("p_length", p.length()); // should
test for null first!
}
Getting the string again from the request is redundant with the
original code; another reason to consider adding the logic to
processRequest, instead.
Note: I'm assuming that you don't want to change the redirection to
index.jsp logic. If you want to redirect somewhere else, you could use
around advice to override the original behavior, but I don't recommend
it for two reasons. 1) YOu'll have to reproduce most of the
processRequest logic in the advice, since you won't be able to call
"proceed", since it will do the old redirect. 2) Because of #1, you
won't be able to call "proceed", so your design will violate the
"principle of least surprise"; if someone reads the servlet code, they
will expect it to be executed, but in fact the aspect will "hijack"
the control flow and reproduce all the logic in the around advice
instead. So, if you need to change the control flow, you really
should just modify the original method. I hope all that made sense...
For help on using AspectJ with Servlets, Russ Miles "AspectJ
Cookbook" (O'Reilly) discusses this in Chapter 3.
There is also this example on the Eclipse site:
http://www.eclipse.org/aspectj/sample-code.html#j2ee-servlets
Presumably, it's also in the online help for AJDT!
See also this article in the [EMAIL PROTECTED] series by Ron Bodkin:
http://www.ibm.com/developerworks/java/library/j-aopwork10/
dean
On Jan 23, 2008, at 8:05 AM, kissm1985 wrote:
Hi all,
I'm quite new to AOP and have a quiestion about using AspectJ to
modularize
crosscutting properties in servlets. It would be helpful to find a
solution
for this problem:
I have a servlet wich gets a parameter from a jsp (form) and
forwards it to
an other....
...
protected void processRequest(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
try {
String p = (String)request.getParameter("p");
request.setAttribute("p", p);
request.getRequestDispatcher("Index.jsp").forward(request,
response);
} catch (Exception e) {
e.printStackTrace();
}
}
...
Now I would like to implement a new requirement : "count the
carachters of
the string parameter and forward it to Index.jsp". How can I do it
with
AspectJ? I have the idea (the execution of the getParameter have to be
cougth by a pointcut, and after:pointcut the aspect have to post
this value
(length) to Index.jsp) but I haven't the syntax. Can please you help
me?
Thanks,
Istvan
--
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Dean Wampler, Ph.D.
dean at objectmentor.com
http://www.objectmentor.com
See also:
http://www.aspectprogramming.com AOP advocacy site
http://aquarium.rubyforge.org AOP for Ruby
http://www.contract4j.org Design by Contract for Java5
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