Flash (JSF API 2.3.1 2.3.1 API)

java.lang.Object
- javax.faces.context.Flash

All Implemented Interfaces:

Map<String,Object>

Direct Known Subclasses:

ELFlash, FlashWrapper, NoOpFlash
```
public abstract class Flash
extends Object
implements Map<String,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 JSF 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 EL implicit object flash and also via ExternalContext.getFlash(). The implementation must ensure that the flash is usable from both JSP and from Facelets for JSF 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 the EL as well, as described in the javadocs.

EL Usage Example
First page
```
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:c="http://xmlns.jcp.org/jsp/jstl/core">

  <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">

  <h:outputText value="#{flash.foo}" /> will be "fooValue"
  without the quotes.
```
The same usage syntax must be available in JSP.

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.
Since:

2.0

Nested Class Summary
- Nested classes/interfaces inherited from interface java.util.Map
  Map.Entry<K,V>

Field Summary

Fields
Modifier and Type	Field and Description
`static 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.

Constructor Summary

Constructors
Constructor and Description

Flash()

Constructors
Constructor and Description
`Flash()`

Method Summary

All Methods Instance Methods Abstract Methods
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(String key)` Causes a value stored with a previous call to `putNow(java.lang.String, java.lang.Object)`, its EL 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.
`abstract void`	`putNow(String key, 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 `keepMessages` JavaBeans property.
`abstract void`	`setRedirect(boolean newValue)` Setting this property to `true` 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

- Field Detail
  - NULL_VALUE
```
public static final 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.
    
    See Also:
    
    Constant Field Values
- Constructor Detail
  - Flash
```
public Flash()
```
- Method Detail
  - 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 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.
    EL Usage Example
    
    First page
    
    <html xmlns="http://www.w3.org/1999/xhtml" xmlns:c="http://xmlns.jcp.org/jsp/jstl/core">  <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">  <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. See isKeepMessages().
    
    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 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.
    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 return true.
    EL Usage Example
    
    <html xmlns="http://www.w3.org/1999/xhtml" xmlns:c="http://xmlns.jcp.org/jsp/jstl/core">  <c:set target="#{flash}" property="redirect" value="true" />
    Parameters:
    
    newValue - the new value for this property on this session.
    
    Since:
    
    2.0
  - putNow
```
public abstract void putNow(String key,
                            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.
    EL Usage Example
    
    <html xmlns="http://www.w3.org/1999/xhtml" xmlns:c="http://xmlns.jcp.org/jsp/jstl/core">  <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 entry
    
    value - the value for this entry
    
    Since:
    
    2.0
  - keep
```
public abstract void keep(String key)
```
    Causes a value stored with a previous call to putNow(java.lang.String, java.lang.Object), its EL 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.
    
    Parameters:
    
    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.
  - doPrePhaseActions
```
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.
    
    Parameters:
    
    ctx - the FacesContext for this request.
  - doPostPhaseActions
```
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.
    
    Parameters:
    
    ctx - the FacesContext for this request.

Class Flash

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Methods inherited from interface java.util.Map

Field Detail

NULL_VALUE

Constructor Detail

Flash

Method Detail

isKeepMessages

setKeepMessages

isRedirect

setRedirect

putNow

keep

doPrePhaseActions

doPostPhaseActions