Previous answer is correct, but just for completeness I would like to say there have been a lot of issues in Mojarra implementations with all this stuff, but finally they achieved to make it work properly in Mojarra 2.1.27 and 2.2.5 versions.
As @Gamb says, the aim of the flash scope is to keep a parameter alive mapping it internally across redirection. We can also keep the parameter alive for longer if we need it. Apart from the mentioned way , FacesContext#getCurrentInstance#getExternalContext#getFlash#put, there's also the chance to set the parameter via EL expression, using <c:set />. I've implemented a basic test following SSCCE which shows a broader range of options, using two views:
Bean1
@ManagedBean
@ViewScoped
public class Bean1 implements Serializable {
/**
* Just takes the given param, sets it into flash context and redirects to
* page2
*
* @param inputValue
* @return
*/
public String goPage2(String inputValue) {
FacesContext.getCurrentInstance().getExternalContext().getFlash()
.put("param", inputValue);
return "page2?faces-redirect=true";
}
}
page1.xhtml
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:ui="http://java.sun.com/jsf/facelets"
xmlns:c="http://java.sun.com/jsp/jstl/core">
<h:head />
<h:body>
<!-- Sets the first flash param at the action method, which redirects to page 2 -->
<h:form>
<h:inputText value="#{inputValue}" />
<h:commandButton action="#{bean1.goPage2(inputValue)}"
value="Go Page 2" />
</h:form>
<!-- Sets the second flash param -->
<c:set target="#{flash}" property="param2" value="Myparam2" />
<!-- Tries to retrieve both of the params.
Note none of them is displayed at the first page hit.
If page refreshed, the second param which has been already set
using c:set above, will be displayed -->
<p>Param1: #{flash['param']}</p>
<p>Param2: #{flash['param2']}</p>
</h:body>
</html>
Bean2
@ManagedBean
@ViewScoped
public class Bean2 implements Serializable {
public String getParam() {
/**
* Takes the parameter from the flash context
*/
return (String) FacesContext.getCurrentInstance().getExternalContext()
.getFlash().get("param");
}
}
page2.xhtml
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:ui="http://java.sun.com/jsf/facelets"
xmlns:f="http://java.sun.com/jsf/core">
<h:head />
<!-- This page just displays the received params -->
<h:body>
<!-- Different ways to retrieve the params from the flash scope -->
<p>Param1: #{bean2.param}</p>
<p>Param1: #{flash.param}</p>
<p>Param1: #{flash['param']}</p>
<p>Param2: #{flash['param2']}</p>
<!-- Keep the first param for next redirection -->
#{flash.keep.param}
<!-- Return to page1 and see how the first param is retained -->
<h:button outcome="page1?faces-redirect=true" value="return to 1" />
</h:body>
</html>
See also:
