Datamodel.java

// MyController.java :

@ManagedBean
public class MyController {
	
	private DataModel<User> dataModel;

	public DataModel<User> getDataModel() {
		if(dataModel == null) {
			List<User> users = userService.getAll();
			dataModel = new ListDataModel(users);
		}
		return dataModel;
	}
}

// view.xhtml :

<h:datatable value="#{myController.dataModel}" var="u">
	<h:column>
		<f:facet name="header">
			Firstname
		</f:facet>
		#{u.firstname}
	</h:column>

	<h:column>
		<f:facet name="header">
			Lastname
		</f:facet>
		#{u.lastname}
	</h:column>
</h:datatable>