Hi,
I believe that the "views in session" stuff is intended only to handle
back-button usage, NOT to cache pages when a user returns to it via
other means. There is a counter rendered into each page, and only if
(view-id, counter) match a cached view is it reused; this will only
happen when back is clicked. If the user instead clicks a normal link or
command that navigates to that page, the counter will have been
incremented so the old cached view data doesn't match.
See:
JspStateManagerImpl.getSerializedViewFromServletSession
I expect that this feature doesn't work well with session-scope managed
beans (which aren't a good idea anyway IMO).
Yes, this will use some memory; if you don't want to support back-button
use by your webapp's users then you can reduce or disable this feature.
However for most pages the component tree isn't particularly large. If
you are using t:saveState extensively though then data usage can be higher.
The Trinidad (formerly ADFFaces) library does use some clever tricks to
try to cache views for reuse but that is something entirely different.
Regards,
Simon
David Delbecq wrote:
Hi again,
seems i was mistaken on the meaning of this parameter, my apologizes. It
specify the number of view AND states stored (thus not only the view
structure as i thought). Anyway, if you think this value does not fit
your needs, just change it:
<context-param>
<param-name>org.apache.myfaces.NUMBER_OF_VIEWS_IN_SESSION</param-name>
<param-value>20</param-value>
<description>Only applicable if state saving method is "server" (=
default).
Defines the amount (default = 20) of the latest views are
stored in session.
</description>
</context-param>
http://wiki.apache.org/myfaces/Performance
Randahl Fink Isaksen a écrit :
Thanks David - that was very informative.
I can't help but thinking that quite many applications would want to
lower the NUMBER_OF_VIEWS_IN_SESSION from the default 20. I mean if
the user really visits the same website 20 times and thus sees view 1,
2, ..., 20, what are the chances that he will go back and visit, say,
view 4? On many sites I would assume that the chance of that is quite
low, which could indicate that a much lower number would be relevant.
Suppose you lower the NUMBER_OF_VIEWS_IN_SESSION to, say, 5, there
will obviously be a greater chance that the user will revisit a view
that is no longer cached, but since the server is supposed to be able
to deliver that view pretty fast on his first visit anyway it will of
course also be able to deliver the view quite fast on his second visit
even though the view is not cached.
So why is 20 the default?
Randahl
David Delbecq wrote:
Hi randahl,
I recommend you take a look at the JSF lifecycle and more particulary at
the 'Restore view' and the 'Render response' part.
http://www-128.ibm.com/developerworks/java/library/j-jsf2/#N100A9
The view is a set of components. The components are read (initial view)
with their static values and their EL values and then rendered multiple
time. It's at render time that the 'day/night' should be evaluated. If
you have this in you page:
<myCustomComponents:backgroundColor
calor="#{dayBean.isNight?'#000000':'#FFFFFF'}/> then you are sure that
background color will always be correct as long as dayBean.isNight() is
correct.
Randahl Fink Isaksen a écrit :
I read that the default for NUMBER_OF_VIEWS_IN_SESSION is 20, meaning
that MyFaces will store the latest 20 of a client's views in the
client's session. This made me wonder how MyFaces tells the difference
between the views and how MyFaces know when to reuse a view. For
instance if you visit "/aView.jsf" in a browser how can MyFaces tell
whether that view can be safely stored and reused later in the session
if you visit the same view again?
Let me give an example: Let us say that the view on the address
"/aView.jsf" uses a component which makes the background color of the
page white during daytime and black during the night. If I then visit
the view just before nightfall and receive a white page and then
revisit the view during the same session but right after nightfall,
what color will the view then be? I would think that if the original
view is reused it would still be white even though it should actually
now have changed to black. So how can I as a developer tell MyFaces
whether or not it is safe to store the information about the
background color and for how long the information is valid?
Has anyone found some documentation about this?
Thank you
Randahl
