public abstract class Flash
extends java.lang.Object
implements java.util.Map<java.lang.String,java.lang.Object>
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 Server 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 Server 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="http://xmlns.jcp.org/jsp/jstl/core"> <!-- extra code removed --> <c:set target="#{flash}" property="foo" value="fooValue" />Next page
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:h="http://xmlns.jcp.org/jsf/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="http://xmlns.jcp.org/jsf/core" xmlns:h="http://xmlns.jcp.org/jsf/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.
| Modifier and Type | Field and Description |
|---|---|
static java.lang.String |
NULL_VALUE
Because |
| Constructor and Description |
|---|
Flash() |
| Modifier and Type | Method and Description |
|---|---|
abstract void |
doPostPhaseActions(FacesContext ctx)
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 |
doPrePhaseActions(FacesContext ctx)
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 |
isKeepMessages()
Return the value of this JavaBeans property for the flash for this session. |
abstract boolean |
isRedirect()
Return the value of this property for the flash for this session. |
abstract void |
keep(java.lang.String key)
Causes a value stored with a previous call to |
abstract void |
putNow(java.lang.String key,
java.lang.Object value)
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 for |
abstract void |
setRedirect(boolean newValue)
Setting this property to |
public static final java.lang.String NULL_VALUE
Because null values are not allowed as the source for subclasses of EventObject, such as
PostKeepFlashValueEvent and PostPutFlashValueEvent, this value is substituted for null
as the source in the case when a null value is put to or kept in the flash.
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 current
FacesContext 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="http://xmlns.jcp.org/jsp/jstl/core"> <!-- extra code removed --> <c:set target="#{flash}" property="keepMessages" value="true" />Next page
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:h="http://xmlns.jcp.org/jsf/html"> <!-- extra code removed --> <h:messages /> Any messages present on the first page must be displayed on this page.
public abstract void setKeepMessages(boolean newValue)
Setter for keepMessages JavaBeans property. See isKeepMessages().
newValue - the new value for this property on this session.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 with true as the argument.
The current lifecycle traversal for this session is in the “execute” phase and the previous traversal had
setRedirect(boolean) called with true as the argument.
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 return
true.
Jakarta Expression Language Usage Example
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:c="http://xmlns.jcp.org/jsp/jstl/core"> <!-- extra code removed --> <c:set target="#{flash}" property="redirect" value="true" />
newValue - the new value for this property on this session.public abstract void putNow(java.lang.String key,
java.lang.Object value)
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="http://xmlns.jcp.org/jsp/jstl/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}" />
key - the key for this entryvalue - the value for this entrypublic abstract void keep(java.lang.String key)
Causes a value stored with a previous call to putNow(java.lang.String, java.lang.Object), its Jakarta Expression Language equivalent, or to the
request Map, to be promoted to the flash so that is available on the next traversal through the
lifecycle on this session.
key - if argument key is the name of an entry previously stored to the flash on this traversal
through the lifecycle via a call to putNow(java.lang.String, java.lang.Object), or to a set to the EL expression
#{flash.now.<key>}, or to the request Map, to be promoted to the flash as if a
call to put() or a set to the expression #{flash.<key>} was being called.public abstract void doPrePhaseActions(FacesContext ctx)
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.
ctx - the FacesContext for this request.public abstract void doPostPhaseActions(FacesContext ctx)
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.
ctx - the FacesContext for this request.