By Ultan O'Broin-Oracle on Oct 31, 2010
The Application Developer Framework Faces components (as previously mentioned) allow you to use a variety of messages types (error, warning, and so on) in different ways. For example, errors on components can be shown inline (that is, on the page - figure 1) or in a message dialog (figure 2). This is done by setting the inline property on af:messages to true.
Figure 1: ADF Faces Inline Error Message
Figure 2: ADF Faces Error Message Dialog
But how do you make the decision about whether to show the message inline? To do this you need some user experience guidance. Make the decision based on how the business or UI rule you've designed is validated and on the nature of the user task being performed. Here's a sample decision matrix for message types and scenarios (figure 3) that you might like to consider.
Figure 3: Inline versus Dialog-based Messages Decision Matrix
Of course, this is just a guideline. Natch, designing your flows so that errors aren't necessary at all is the way to go, but hey, let's live in the real world!