JSF 2.2 Flash Scope Example

JSF 2.2 Flash Scope Example

In this article I will try to explain you how to use the flash scope in Java EE.

Introduced in JSF 2.0, the flash scope provides a short-lived conversation (flash session). It is a way to pass temporary objects (not only strings) that are propagated across a single view transition and cleaned up before moving on to another view. The flash scope can only be used programmatically as there is no annotation.

In some cases we need to redirect from one view to another view in JSF.  But when we do a redirect we lost everything that is stored in the url with a GET request. One solution is to use an EL expression of the abstract class Flash #{flash.foo}. So, this is a pretty simple solution to redirect without lost anything:

Source files:

index.xhtml
index.xhtml
index.xhtml

The special thing here is the use of #{flash.foo}, where foo is the name of the variable in the flash scope.

 

ExampleController.java
ExampleController.java
ExampleController.java

The goal of this controller is just to do a redirect from the index.xhtml to the target.xhtml.

 

target.xhtml
target.xhtml
target.xhtml

Here we fetch the value of the foo variable by doing again #{flash.foo} to display the data.

The results:
fpage_hello
This is the first page with the message Hello World.

 

2ndpage

And finally this is the second page (target.xhtml) wich displays the message from the previous page.

Final Considerations

We’ve learned how to pass values with the help of flash from one view to another with redirects.

Notice that if you refresh the second page after it shows up, all the data has gone. That’s because the flash scope was destroyed immediately when the rendering of the second page occurs. This is the goal of the flash scope. It just holds some values (in a flash session) between one HTTP request and the subsequent HTTP response.

This type of scope must be done programmatically. There is no annotation, like there is, for example, to the request scope (@RequestScoped).

Please feel free to comment.

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