a4j:commandButton is similar to the standard h:commandButton, but produces an Ajax request with a further partial page update. 'reRender' attribute points to the component(s) that should be re-rendered in the component tree and updated in the browser DOM after an Ajax Response is completed.

The following example shows how the greeting message is shown on the screen without refreshing the entire page:

CommandButton Demo

For additional information about attributes of this compponent read .