Class Flash
- Direct Known Subclasses:
ELFlash
,FlashWrapper
,NoOpFlash
The Flash concept is taken from Ruby on Rails and provides a way to pass temporary objects between the user views generated by the faces lifecycle. As in Rails, anything one places in the flash will be exposed to the next view encountered by the same user session and then cleared out. It is important to note that “next view” may have the same view id as the previous view.
Implementation Requirements
The flash is a session scoped object that must be thread safe.
The implementation requirements will be described in terms of the runtime traversing the Jakarta Faces
lifecycle. The flash exposes a Map
interface over two logical maps. The choice of which logical map is
accessed depends on the current faces lifecycle phase. One logical map is for the current traversal and the other is
for the next traversal. During the execute portion of the lifecycle, all flash accesses are sent to the current
traversal map. During the render portion of the lifecycle, all flash accesses are sent to the next traversal map. On
the next traversal through the lifecycle, the implementation must ensure that the current traversal map is the next
traversal map of the previous traversal. Here is an example for illustration purposes only.
Consider an initial request to the faces lifecycle
Traversal N, execute phase: skipped on initial request.
Traversal N, render phase: flash access goes to flash[N].
Traversal N+1, execute phase: flash access goes to flash[N].
Traversal N+1, render phase: flash access goes to flash[N+1].
The implementation must ensure the proper behaviour of the flash is preserved even in the case of a
<navigation-case>
that contains a <redirect />
. The implementation must ensure
the proper behavior of the flash is preserved even in the case of adjacent GET requests on the same session. This
allows Faces applications to fully utilize the “Post/Redirect/Get” design pattern.
The implementation must allow the user to access the flash via the Jakarta Expression Language implicit object
flash
and also via ExternalContext.getFlash()
. The implementation must
ensure that the flash is usable from both Jakarta Server Pages and from Facelets for Jakarta Faces 2. In
addition to exposing the Map
interface, there are several features exposed as methods on the
Flash
itself. Each of these features may be accessed via Jakarta Expression Language as well, as
described in the javadocs.
Jakarta Expression Language Usage Example
First page
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:c="jakarta.tags.core"> <!-- extra code removed --> <c:set target="#{flash}" property="foo" value="fooValue" />
Next page
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:h="jakarta.faces.html"> <!-- extra code removed --> <h:outputText value="#{flash.foo}" /> will be "fooValue" without the quotes.
The same usage syntax must be available in Jakarta Server Pages.
Note that extra action must be taken when using the flash in concert with output components that cause the browser to
issue a GET request when clicked, such as h:button
and h:link
. The following example
illustrates one way to use the flash in such circumstances.
First page
<h:button id="nextButton" value="Next (button)" outcome="next.xhtml"> <f:param name="foo" value="bar"/> </h:button>
Next page
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:f="jakarta.faces.core" xmlns:h="jakarta.faces.html"> <f:metadata> <f:viewParam name="foo" id="foo" value="#{flash.now.foo}" /> </f:metadata> <head /><body> foo = #{flash.foo} </body> </html>
Note that this example uses #{flash.now}
on the second page. This is because the value doesn't actuall
enter the flash until the server is processing the GET request sent by the browser due to the button being clicked.
- Since:
- 2.0
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Nested Class Summary
-
Field Summary
Modifier and TypeFieldDescriptionstatic final String
Becausenull
values are not allowed as the source for subclasses ofEventObject
, such asPostKeepFlashValueEvent
andPostPutFlashValueEvent
, this value is substituted fornull
as the source in the case when anull
value is put to or kept in the flash. -
Constructor Summary
-
Method Summary
Modifier and TypeMethodDescriptionabstract void
Called after the execution of every lifecycle phase, this method allows implementations to take the necessary actions to provide the Flash scope contract as it applies to the request procesing lifecycle.abstract void
Called before the execution of every lifecycle phase, this method allows implementations to take the necessary actions to provide the Flash scope contract as it applies to the request procesing lifecycle.abstract boolean
Return the value of this JavaBeans property for the flash for this session.abstract boolean
Return the value of this property for the flash for this session.abstract void
Causes a value stored with a previous call toputNow(java.lang.String, java.lang.Object)
, its Jakarta Expression Language equivalent, or to the requestMap
, to be promoted to the flash so that is available on the next traversal through the lifecycle on this session.abstract void
Puts a value in the flash so that it can be accessed on this traversal of the lifecycle, rather than on the next traversal.abstract void
setKeepMessages
(boolean newValue) Setter forkeepMessages
JavaBeans property.abstract void
setRedirect
(boolean newValue) Setting this property totrue
indicates that the next request on this session will be a redirect.Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Methods inherited from interface java.util.Map
clear, compute, computeIfAbsent, computeIfPresent, containsKey, containsValue, entrySet, equals, forEach, get, getOrDefault, hashCode, isEmpty, keySet, merge, put, putAll, putIfAbsent, remove, remove, replace, replace, replaceAll, size, values
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Field Details
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NULL_VALUE
Because
null
values are not allowed as the source for subclasses ofEventObject
, such asPostKeepFlashValueEvent
andPostPutFlashValueEvent
, this value is substituted fornull
as the source in the case when anull
value is put to or kept in the flash.- See Also:
-
-
Constructor Details
-
Flash
public Flash()
-
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Method Details
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isKeepMessages
public abstract boolean isKeepMessages()Return the value of this JavaBeans property for the flash for this session. This value determines whether or not any
FacesMessage
instances queued in the currentFacesContext
must be preserved so they are accessible on the next traversal of the lifecycle on this session, regardless of the request being a redirect after post, or a normal postback.Map
accesses for the special key “keepMessages
” must return the value of this JavaBeans property.Jakarta Expression Language Usage Example
First page
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:c="jakarta.tags.core"> <!-- extra code removed --> <c:set target="#{flash}" property="keepMessages" value="true" />
Next page
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:h="jakarta.faces.html"> <!-- extra code removed --> <h:messages /> Any messages present on the first page must be displayed on this page.
- Returns:
- the boolean flag whether keeping messages or not.
- Since:
- 2.0
-
setKeepMessages
public abstract void setKeepMessages(boolean newValue) Setter for
keepMessages
JavaBeans property. SeeisKeepMessages()
.- Parameters:
newValue
- the new value for this property on this session.- Since:
- 2.0
-
isRedirect
public abstract boolean isRedirect()Return the value of this property for the flash for this session. This must be
false
unless:-
setRedirect(boolean)
was called for the current lifecycle traversal withtrue
as the argument. -
The current lifecycle traversal for this session is in the “execute” phase and the previous traversal had
setRedirect(boolean)
called withtrue
as the argument.
- Returns:
- the value of this property for the flash for this session.
-
-
setRedirect
public abstract void setRedirect(boolean newValue) Setting this property to
true
indicates that the next request on this session will be a redirect. Recall that on a redirect, the server sends a special response to the client instructing it to issue a new request to a specific URI. The implementation must insure that reading the value of this property on that request will returntrue
.Jakarta Expression Language Usage Example
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:c="jakarta.tags.core"> <!-- extra code removed --> <c:set target="#{flash}" property="redirect" value="true" />
- Parameters:
newValue
- the new value for this property on this session.- Since:
- 2.0
-
putNow
Puts a value in the flash so that it can be accessed on this traversal of the lifecycle, rather than on the next traversal. This is simply an alias for putting a value in the request map.
Jakarta Expression Language Usage Example
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:c="jakarta.tags.core"> <!-- extra code removed --> <c:set target="#{flash.now}" property="bar" value="barValue" /> <p>Value of \#{flash.now.bar}, should be barValue.</p> <h:outputText value="#{flash.now.bar}" />
- Parameters:
key
- the key for this entryvalue
- the value for this entry- Since:
- 2.0
-
keep
Causes a value stored with a previous call to
putNow(java.lang.String, java.lang.Object)
, its Jakarta Expression Language equivalent, or to the requestMap
, to be promoted to the flash so that is available on the next traversal through the lifecycle on this session.- Parameters:
key
- if argumentkey
is the name of an entry previously stored to the flash on this traversal through the lifecycle via a call toputNow(java.lang.String, java.lang.Object)
, or to a set to the EL expression#{flash.now.<key>}
, or to the requestMap
, to be promoted to the flash as if a call toput()
or a set to the expression#{flash.<key>}
was being called.
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doPrePhaseActions
Called before the execution of every lifecycle phase, this method allows implementations to take the necessary actions to provide the Flash scope contract as it applies to the request procesing lifecycle.
- Parameters:
ctx
- theFacesContext
for this request.
-
doPostPhaseActions
Called after the execution of every lifecycle phase, this method allows implementations to take the necessary actions to provide the Flash scope contract as it applies to the request procesing lifecycle.
- Parameters:
ctx
- theFacesContext
for this request.
-