I debug, so when I click on the button delete it passing to Servlet, but when it arrives on "Integer ca = Integer.parseInt(request.getParameter("cmpCa"))" is throw a exception saying it's null.
Do you understand me?
I don't see any tag with name "cmpCa" on your JSP page. That's why you are getting null for when you try to search for "cmpCa" on request object.
Now the button delete works normally, however the button update doesn't works.
Yes it should wok because it doesn't execute the following condition :
Normally what i will do for debugging is to change the form method from post to get in jsp to check the parameter and value that are to my service method. I would suggest the same for you to check for the presence of any parameter with name "cmpCa".
There is no need to change the method to GET to check the HTTP parameters. All modern browsers have built-in debugging tools that can be used to inspect the network traffic without resorting to changing the code.