JSF analogous to Struts Tokens?

Question

Hi!
I would like to know if there is any feature in JSF that is similar to Struts Tokens?
My Specific requirement is :
After filling the form (in a wizard kind of interface)the fields would be persisted , but the user might click the back button to make sure that he entered the data correctly, and then may click next
button, which triggers a duplicate data error, because the user has already entered the data ,and that is persisted.
In Struts we would do Action .savetokens in the submit action
and check for the validity of the token by caling Action.isTokenValid(),if the conditions is true, thaty means the form has been already submitted.
Like wise is there any thing that resembles this feature of Struts in JSF ?
May be savestate and restorestate could be a solution..
Any thoughts..?
Regards,
Samba

Answer 1

Hi! Simon,
From Apache trinidad Documentation :
Some Apache Trinidad configuration options are set instead with <context-param> elements in your WEB-INF/web.xmlfile.
org.apache.myfaces.trinidad.CACHE_VIEW_ROOT
Enables or disables UIViewRoot caching; defaults to true.
When "token" client-side state saving is enabled, Trinidad applies an additional optimization by caching an entire UIViewRoot tree with each token. (Care has been taken to ensure that this does not affect thread safety or session failover.) This is a major optimization for AJAX-intensive systems, as postbacks can be processed far more rapidly without the need to reinstantiate the UIViewRoot tree. However, it is known to interfere with some other JSF technologies. In particular, the Apache MyFaces Tomahawk saveState component does not work, and template text in Facelets may appear in duplicate. This optimization can be disabled by setting this context parameter to false.
org.apache.myfaces.trinidad.CLIENT_STATE_METHOD
Chooses the type of client-side state saving used when client-side state saving is enabled (with the JSF standard javax.faces.STATE_SAVING_METHOD parameter). Two values are accepted:
* "token": the default, which stores page state in the session, but persists a token to the client that lets Apache Trinidad disambiguate the same page appearing multiple times. Failover is supported.
* "all": stores all state in the client in a (potentially large) hidden form field. This matches the default behavior of the JSF reference implementation, and can be useful for developers avoiding any use of HttpSession.
org.apache.myfaces.trinidad.CLIENT_STATE_MAX_TOKENS
In "token"-based client-side state saving, chooses how many tokens should be preserved at any one time. The default value is 15. When this is exceeded, state will have effectively been "forgotten" for the least recently viewed pages, which can impact users that actively use the Back button or that have multiple windows open simultaneously. Developers building HTML applications that rely heavily on frames will likely need to increase this value.
org.apache.myfaces.trinidad.USE_APPLICATION_VIEW_CACHE
This configuration option enables an optimized strategy for caching some view state at an application level, which significantly improves scalability. However, it makes it harder to develop (updates to pages will not be noticed until the server is restarted), and in some rare cases cannot be used for some pages. See below for more information about this option.
What i'm interested in knowing more about is this :
We can get the token written to the Web page as a ViewState hidden variable by calling facesContext.saveState();
Can we use this token to Compare whether the user has already submitted a request, and identify that he now posting a duplicate request?
I'll give it a try,any way.
And coming to your suggestion of using pageFlowScope ----
We regularly use that to save a flag which is set to true on form submission ,and corresponding persistence ,and later if the user clicks the back button,and submits the form again, we'll check for the flag ,and since the value is true, we would silently continue with the decision to move to the next page this time leaving out persistence;unless ,of course in the scenario where the form fields might have changed in the second submission of the form in which case , we need to update the values that have already been entered ... and this involves a lot many issues to discuss ,than mentioned here.
but my intention is to know whether there is an in-built functionality in JSF that addresses this issue as did the Struts!
I strongly believe that viewState Token should be a very good candidate for this feature.
Am I too idealistic ?
Any thoughts are welcome,
Regards,
Samba