What you are seeing is a natural consequence of the Servlet spec, and in particular the behaviour of the RequestDispatcher. Here are some points to consider:
* When you forward a request, all of the request parameters are preserved and presented to whatever processes the forwarded request. Therefore, it is natural that those original values be used to populate any form bean associated with a forwarded-to action, should the target of the forward happen to be a Struts action. * A forward need not target a Struts action. It may go to a JSP page, another servlet in the web app, or something else. You may happen to know that, for your application, the target is another Struts action, but Struts cannot assume that. * A forwarded-to action does not know that it was forwarded to from another action. It could have been forwarded to from a JSP page, a non-Struts servlet, or something else. Therefore, Struts cannot assume that the form bean has already been populated by some prior action. It seems that you have some very specific assumptions built into your app. In particular, your actions are very tightly coupled. For example, your actions "know" that they are forwarding to another action, and further, they "know" the type and instance of the form bean that the other action will use. This type of coupling is one of the things that Struts really tries hard to avoid. If you really need this kind of tight coupling between your actions, then you can have your actions "agree" on some other location from which they can obtain their form bean, rather than using the one that Struts will pass to your execute() method. -- Martin Cooper ----- Original Message ----- From: "Terrence Xavier" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Thursday, April 18, 2002 11:21 AM Subject: ActionServlet re-populates form upon Actoin => Action call > Dear Struts Developers, > > We have noticed some unexpected behavior with Struts. Basically, if > the HTTPRequest specifies attributes to modify in a struts form, they get > modified on EVERY call to the ActionServlet. An example of this is as > follows. Say that we have a JSP that sets a form attribute, and then we > submit to an Action class. From that Action, we modify the same form > attributes, and then forward to another Action. The problem we are seeing is > that the form attributes get re-set upon entry into the second Action, thus > overwriting our changed values in the form from the first Action. > The normal expected behaviour is that we can change the form > attributes in an Action, and then forward to another action and read those > changed values. However, due to how the ActionServlet processes > HTTPRequests, those values will be replaced with the values specified in the > HTTPRequest. Since the parameters in the HTTPRequest are read-only, we > cannot override this functionality. > We have done extensive testing of this "bug" over the past few days. > We have written a simple project to demonstrate the issue, and have tested > it with Struts 0.5, 1.0.2, and 1.1b1. Each of those versions of Struts > functions the same with regard to this issue. > > Here is what is happening in more detail: > > The ActionServlet processes the HTTPRequest and populates the form > bean from the parameters in the HTTPRequest. This occurs before > instantiating the Action class to "perform". Thus, if we forward from Action > to Action, when the same request is passed by the servlet engine, the form > bean gets populated twice -- before and after the first Action. So form bean > values set within the Action that are also present in the HTTPRequest get > overridden with the values from the HTTPRequest. > Our simple project (attached to this e-mail) demonstrates this. > Here's the flow of that project: > > > JSP => Action1 => Action2 => etc... > | | | | | > V V V V V > set(x)=2 (x=2) set(x)=4 (x=2) get(x)=2 > > > In our project, whenever we enter and leave an action, we print out > a string indicating that we are entering or leaving the action. We also have > print statements inside every getter and setter in the form bean that will > tell us whenever anything is retrieved or set in the form. This is the > output we get from our application (with extra a couple comments to help > explain what is going on): > > *********** startActionOne **************START > formAction : setFormAction() originalValue > *********** startActionOne **************END > +++++++++++ One.jsp +++++++++ > formAction : setFormAction() changedbyOneJSP <-- Struts sets the form > bean attribute from JSP. > *********** ActionOne **************START > formAction : getFormAction() changedbyOneJSP > formAction : setFormAction() changedbyActionOne > *********** ActionOne **************END > formAction : setFormAction() changedbyOneJSP <-- Unexpected behavior > occurs here > *********** StartActionTwo **************START > formAction : setFormAction() changedbystartActionTwo > *********** StartActionTwo **************END > +++++++++++ Two.jsp +++++++++ getFormAction() = changedbyOneJSP > > > It is easy to see why this behaviour would be unexpected. After > explicitly setting the "formAction" attribute of the form in ActionOne, it > is re-set by Struts before ActionTwo is "performed". > > Given that this is how Struts functions, our questions are these: > > 1) We have work-arounds by using session request attributes, but we > would like to set form values in actions. How do we do this within the > Struts framework and have them retain their values? > > 2) Since Struts seems to process the request twice, setting the form > attributes over and over again for each action that is forwarded to, does it > make sense to change Struts so that it does not do the same work on the same > HTTPRequest object more than once? > > 3) Is this well-known issue? > > We would appreciate any input you can offer. > > Sincerely, > > Daryl Beattie and Terrence Xavier > > P.S. The example code is configured to work with Struts 1.1b1 right now. We > used the same project to test the other versions, but have since changed it > to use 1.1b1. We did not include the jars in our zip file, so if you want to > try it you will have to copy the Struts jars (and its dependent jars) in the > WEB-INF/lib folder. > > > > ---------------------------------------------------------------------------- ---- > -- > To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> > For additional commands, e-mail: <mailto:[EMAIL PROTECTED]> -- To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> For additional commands, e-mail: <mailto:[EMAIL PROTECTED]>
