Simple example of writing a client behavior

The "client behavior" idea refer to the fact that a client (user) can perform an action over a component (click, blur, focus, mouse over, mouse out, etc) and trigger a specific behavior. As you can see, the actions performed by the user will cause HTML events (e.g. onchange, onclick, onmouseover, onmouseout, onkeydown, onload), and those events will be transformed in behaviors via JavaScript snippets of code that runs on client machine, in his browser. The behaviors was already rendered by JSF as pieces of JavaScript, and there are available on client.

Technically speaking, the ClientBehavior interface (and the ClientBehaviorBase which is a convenience base class that implements the default concrete behavior of all methods defined by ClientBehavior) defines the mechanism by which client behavior implementations generate scripts. The most important method on the ClientBehavior interface is getScript():

public String getScript(ClientBehaviorContext context)

The getScript() method returns a string that contains a JavaScript code suitable for inclusion in a DOM event handler. The method’s single argument, the ClientBehaviorContext, provides access to information that may be useful during script generation, such as the FacesContext and the UIComponent to which the behavior is being attached.

Let's see an example. We simply render a button that is capable to delete some files when is clicked. But, before deleting the files we render a confirmation dialog. The piece of JavaScript that output the confirmation dialog is returned by a ClientBehaviorBase, and the HTML event is onclick - this is the default event for <h:commandButton/>.

1. The index.xhtml page looks like this:

<h:body>

 <h:form>

  <h:commandButton value="Delete" action="done">

   <b:confirmDelete/>

  </h:commandButton>

 </h:form>

</h:body>

2. The ClientBehaviorBase looks like this:

@FacesBehavior(value = "confirm")

public class ConfirmDeleteBehavior extends ClientBehaviorBase {  

   

 @Override

 public String getScript(ClientBehaviorContext behaviorContext) {

  return "return confirm('Are you sure you want to delete this file ?');";

 }

}

3. The delete.taglib.xml looks like this:

<facelet-taglib version="2.2"

                xmlns="http://xmlns.jcp.org/xml/ns/javaee"

                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

                xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee

                http://xmlns.jcp.org/xml/ns/javaee/web-facelettaglibrary_2_2.xsd">

 <namespace>http://www.custom.tags/jsf/delete</namespace>

  <tag>

   <tag-name>confirmDelete</tag-name>

   <behavior>

    <behavior-id>confirm</behavior-id>

   </behavior>

  </tag>

</facelet-taglib>

 

The complete example is available here.