jsf 2 - How to keep JSF flash scope parameters on page reload?

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jsf 2 - How to keep JSF flash scope parameters on page reload?

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

jsf 2 - How to keep JSF flash scope parameters on page reload?

I use flash scope to pass a setting object between @viewscoped contollers. But if I make a page reload on one of them, then the flash map is empty and the setting object is not initialized. Is it possible to keep flash scope on page reload?

My source code to store/retrieve settings:

FistPage.xhtml

...
<p:commandButton value="next"
    action="#{firstPageController.transferConfig}"  
    process="@this" />
...

FirstPageController.java

@ManagedBean(name = "firstPageController")
@ViewScoped
public class FirstPageController {
...
public String transferConfig() {
FacesContext.getCurrentInstance().getExternalContext().getFlash().put("searchConfig",   searchConfig);
return "/secondPage.xhtml?faces-redirect=true";
}
...
}

SecondPage.xhtml

...
<h:outputLabel value="value">
    <f:event type="preRenderComponent" listener="#{secondPageController.onPageLoad()}"/>
</h:outputLabel>
...

SecondPageController.java

@ManagedBean(name = "secondPageController")
@ViewScoped
public class SecondPageController {
    ...
    public void onPageLoad() 
    {
        flash = FacesContext.getCurrentInstance().getExternalContext().getFlash();

        searchConfig = ((SearchFilterConfig) flash.get("searchConfig"));

        flash.putNow("searchConfig", searchConfig);

        flash.keep("searchConfig");
    }
    ...
}

I use Mojarra 2.1.29

Thanks

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1 Answer

深蓝 · Answer 1 · 2021-10-17T01:13:35+0000

I just did some tests in my playground project and realized it's actually possible to keep the state of the flash parameters even if you GET the page again, using {flash.keep}. That's how the JSF docs explain it:

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.

Here you've got a nice basic test case:

page1.xhtml

<html xmlns="http://www.w3.org/1999/xhtml"
    xmlns:h="http://xmlns.jcp.org/jsf/html"
    xmlns:c="http://java.sun.com/jsp/jstl/core">
<h:head />
<h:body>
    <h:form>
        <h:button id="nextButton" value="Next (button)" outcome="page2.xhtml" />
        <c:set target="#{flash}" property="foo" value="bar" />
    </h:form>
</h:body>
</html>

page2.xhtml

<html xmlns="http://www.w3.org/1999/xhtml"
    xmlns:f="http://java.sun.com/jsf/core"
    xmlns:h="http://java.sun.com/jsf/html">
<head />
<body>foo = #{flash.keep.foo}
</body>
</html>

Just open the first page and click on the button which will redirect you to the second one. Then refresh the second page as many times as you want and you'll find the parameter persisting.

Tested in Mojarra 2.2.6

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jsf 2 - How to keep JSF flash scope parameters on page reload?

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