One small tangent on why you might still want to call session.setAttribute. If you ever want your app to work in a clustered/distributed environment, you should always call session.setAttribute after modifying the state of a session attribute. It may seem redundant:
Address address = ...; Object customer = session.getAttribute(Constants.CUSTOMER_KEY); PropertyUtils.setProperty(customer, "address", address); session.setAttribute(Constants.CUSTOMER_KEY, customer); but it's really the simplest way for a container to determine that an attribute has been added or changed and should be replicated. Quoting "Mainguy, Mike" <[EMAIL PROTECTED]>: > Welll, > Common misconception, but, technically all java calls are "by value". > That is, there is no such thing in java as passing something "by > reference". > The hook is, the value passed in when something is an Object is actually a > reference (aka a pointer) to the existing object. > While you can manipulate the thing that this points to, you cannot reassign > it point to something else. I got all bunged up about this also and I > think > it's a pretty important point that can easily be missed if you came into > java from another language that allows "by reference" calls. > > By saying that objects are passed "by reference" folks are actually making > things more complicated than they need to be... For a really good > explanation see http://www.yoda.arachsys.com/java/passing.html > > > > worse is better > > -----Original Message----- > From: Larry Meadors [mailto:[EMAIL PROTECTED] > Sent: Monday, December 01, 2003 10:52 AM > To: [EMAIL PROTECTED] > Subject: Re: Question regarding ActionForms. > > > Welcome to java 101, formerly known as the struts-users mailing list. > > Object references are passed to method calls. While that reference cannot > be > changed, the object that it references can. On the other hand, if you > create > a new action form and assign it to the "form" parameter, nothing will > happen > because that reference cannot be changed. > > Larry > > >>> [EMAIL PROTECTED] 12/01/03 8:42 AM >>> > Hi, > > I am currently using Struts 1.0.2 and have notice something with regard to > handling of ActionForms. > > Why is it, that in the "perform()" method of my Action I am able to modify > the passed-in ActionForm and all modifications that I make to the > ActionForm > in my Action have effect on the ActionForm in the session, without the need > to reset the modified form in the session. e.g. > > public ActionForward peform(ActionMapping mapping, > ActionForm form, > HttpServletRequest request, > HttpServletResponse response, > )throws IOException, ServletException > > { > MyForm myForm = (MyForm)form; > > form.setMemberA("valA"); > form.setMemberB("valB"); > > // why dont I have to do the following: session.setAttribute > ("myFormName", myForm); > > return "success"; > > } > > I thought that since Java passes method arguments by value and not by > reference, then I would have to reset my modifed copy back into the session > for changes on the form to be visible in the form in the session ? > > Any insights on how this mechanism works would be greatly appreciated. > > Thanks, > > Sepand -- Kris Schneider <mailto:[EMAIL PROTECTED]> D.O.Tech <http://www.dotech.com/> --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
