Practical RichFaces, Second Edition

CHAPTER 2 GETTING STARTED
In JSF, the view is rendered on the server. When we add Ajax, the view is still rendered on the
server—we just don’t need to render everything. We render specified components and thus we refer to it
as partial view rendering. When the rendered response (after an Ajax request) is sent to the browser,
that’s where the partial page update happens in the browser. There is a JavaScript library that takes the
response and does the DOM (Document Object Model) update. It’s fine to use a partial page update or
partial view rendering—as long as you understand that the markup is rendered on the server and the
actual page update happens in the browser.
Partial View Processing
Without Ajax, when a page (form) is submitted, the entire form is processed on the server. When we say
processed on the server, we refer to input or action components that go through the JSF life cycle; in
particular, phases such as Apply Request Values, Process Validation, Update Model, and Invoke
Application.
Again, without Ajax it’s simple. The entire form or all the components within the form are
processed. When working with Ajax, the situation is different. We might want only a particular
component to be processed and not process all other components; for example, if we only want to
validate one component and don’t need to validate anything else. In such case, we need to be able to
select which component is processed.
Deciding what to process is done via the execute attribute, described in Table 2-4.
Table 2-4. Execute attribute
Attribute Description
execute Determines ids of components to be processed on server.
The execute attribute can have different values, as shown in Table 2-5.
Table 2-5. Execute attribute values
Attribute Description
@all Process all components in the view.
@none Process no components in the view.
@this Process only this component, the component that triggered the Ajax request (default).
@form Process all components within this form (from which Ajax request was fired).
ids Implicit ids of components to be processed, space separated.
EL Process ids resolved form Collection of strings.
Notice that default value is @this, which means that the component firing the Ajax request will be
processed by default. Listing 2-17 shows an example.