Ralph's Open Source Blog

Using JSF 2.0 and Ajax simplifies the web design and provides a lot of cool tricks to extend the user experience. With the render and execute tags form the f:ajax tag it is use to update components dynamically.

But in the past I run often into problems when trying to update a component outside the current ui context. For example when you try to update a part of your form for a single row in h:datatable component you will typically see log messages like this one:

f:ajax contains an unknown id 'j_idt90:painelTabela' - cannot locate it in the context of the component j_idt75

To solve such kind of problems you need to specify the full component id to be rendered or executed. This is not always as easy at it sounds. When your component is nested in a complex component tree the component id can be prafixed with a long list of parent component ids. This happens typically in h:datatables, ui:repeats or c:forEach sections.

One solution is to navigate back in the tree to the correct ui node and get the componentID using an EL syntax like this:

<f:ajax render=":#{component.parent.parent.parent.parent.clientId}:new-minute-panel:" />

This looks not really nice and it creates new problems when you redesign or move your ui components into a new structure on your jsf page.

A simple trick to solve the problem is to bind the component which need to be rendered into a ui param. So you can reference its full clientId in the ajax context. See the following example:

<h:panelGroup layout="block" id="mylist" binding="#{myListComponent}">                
   <ui:repeat var="attachment" value="#{myController.myList}">
       ....
       <!-- some ajax functionality... -->
       <f:ajax render=":#{myListComponent.clientId}">
           <h:commandLink actionListener="#{myController.soSomething}">click me</h:commandLink>
       </f:ajax>
 ...
   </ui:repeat>
....

In this example I use the binding tag to bind the panelGroup to a param named ‘myListComponent’. Inside the ui:repeat I can now access the outer component and render the component fom my f:ajax element accessing the clientId

<f:ajax render=":#{myListComponent.clientId}"

As a result the ajax component no longer depends on the position in my page and I can reuse it in any part of my jsf page.

TRANSFER CLIENTIDS TO SUBFORMS

Another solution using the binding is to transfer a component into a subform. See the following example:

 <h:panelGroup id="my_panel" binding="#{myListComponent}">
     <h:dataTable id="mydatatable" value="#{myController.myList}" var="child">
       .....
        <ui:include src="/forms/sub_myeditor.xhtml" >
            <ui:param name="myPanel" value="#{myListComponent}" />            
        </ui:include>
       .....
     </h:dataTable>

In this example I transfer the ui:component containing my h:datatable to a subpage ‘sub_myeditor.xhtml’  which is included inside the table. Now I can access the panelGroup inside my subpage and render it after an ajax event:

<h:commandButton ....  >
       <f:ajax render=":#{myListComponent.clientId}" 
                execute=":#{myListComponent.clientId}"/>
</h:commandButton>

Also in this example the component in the ajax tag is addressed with its absolute path.

Since JSF 2.0 has introduced the ajax support it is quite simple to implement functional widgets like a suggestion input box. The following short tutorial shows how to build your own suggestion widget using JSF 2.0 and it’s ajax capabilities.

1. THE HTML FORM

First you need a simple input field where the user can type in a search phrase. This can be done wit the h:inputText element. After the user typed in some character a suggestion widget should start a backend search and provide the user with a list of suggestions (you can see this behaviour when searching for something on google.com). To connect your inputText element with a backend component you can use the new build-in ajax feature provided by JSF 2.0. So your input element looks something like this:

<h:panelGroup layout="block" style="margin-bottom:5px;">
     <h:inputText value="#{suggestController.input}">
        <f:ajax event="keyup"  render="suggest_box" /> 
     </h:inputText>
</h:panelGroup>

 

2. DEFINE THE SUGGEST BOX

With the ‘render’ attribute of the f:ajax tag you specify which part of your page should be rerendered after the ajax event was fired. In this case an element with the ID ‘suggest_box’ will be updated. This is the part where you can display the results of your backend search:

<h:panelGroup id="suggest_box">
	<ul>
		<ui:repeat var="entry" value="#{suggestController.result}">
			<li>#{entry}</li>
		</ui:repeat>
	</ul>
</h:panelGroup>

 

To bind you backend component (suggestController) to the event just use the listener tag:

 <f:ajax event="keyup" render="suggest_box"
	listener="#{suggestController.search}" >
</f:ajax>

Your suggest controller implementation can look like this:

....
public void search(AjaxBehaviorEvent event) {
	....
	result=new ArrayList<String>();
	....
}

public List<String> getResult() {
	return result;
}

If you are working with EL 2.2 support (GlassFish 3.1) you can also pass params as method arguments:

<f:ajax event="keyup" render="suggest_box"
	listener="#{suggestController.search('abc')}" >
</f:ajax>

public void search(String param) {
       ..
}

 

3) LAYOUT

Now you can do some layout stuff. Typically the suggestion box should only be displayed with a user typed in a search phrase. And the suggestion box should hidden if the focus is lost. This can be done with some css definition:

.suggestbox {
	position: relative;
}

.suggestbox .resultlist {
	display: block;
	position: absolute;
	z-index: 1;
	left: 2px;
	top: 22px;
	border: 1px solid #CCC;
	background-color: #EEE;
}

To hide the resultlist you can use the f:ajax event ‘blur’

 <f:ajax event="blur" render="suggest_box"
                    listener="#{suggestController.reset}" />

The listener is bound to a backend method which resets the result list. So you can display the complete box in order of the current result. This is the complete code:

JSF Code:

<h:panelGroup layout="block">
	<!-- Process references -->
	<h:panelGroup layout="block" style="margin-bottom:5px;">
		<h:inputText value="#{suggestController.input}">
			<f:ajax event="keyup" render="suggest_box"
				listener="#{suggestController.search('')}" />
			<f:ajax event="blur" render="suggest_box"
				listener="#{suggestController.reset}" />
		</h:inputText>
	</h:panelGroup>
	<h:panelGroup id="suggest_box">
		<h:panelGroup id="suggest_resultlist"
			rendered="#{! empty suggestController.result}">
			<ul>
				<ui:repeat var="entry" value="#{suggestController.result}">
					<li>#{entry}</li>
				</ui:repeat>
			</ul>
		</h:panelGroup>
	</h:panelGroup>
</h:panelGroup>

 SuggestController:

@Named("suggestController")
@RequestScoped
public class SuggestController implements Serializable {

	private static final long serialVersionUID = 1L;
	private List<String> result=null;
	private String query = null;
	private String input =null;
	
	public SuggestController() {
		super();
		result = new ArrayList<String>();
	}

	public String getQuery() {
		return query;
	}

	public void setQuery(String query) {
		this.query = query;
	}

	public String getInput() {
		return input;
	}

	public void setInput(String input) {
		this.input = input;
	}
	
	public void reset(AjaxBehaviorEvent event) {
		 result=new ArrayList<String>();
	}
	
	public void search(String query) {
    	result=new ArrayList<String>();
		result.add("Hallo "  + System.currentTimeMillis());
		result.add("World "+ + System.currentTimeMillis());

	}
	
	public List<String> getResult() {
		return result;
	}

}

4) DELAY AJAX EVENTS

Maybe you run into a problem with the onblur ajax call to hide your overlay section. If the section contains h:command links or buttons the action and actionListeners will not be called because the ajax blur event hides the overlay to early.

With a trick from BalusC you can delay the blur event a little bit. So just add the following jQuery code into your page:

$(document).ready(function() {
	$(".suggestinput").each(function(index, input) {
	    var onblur = input.onblur;
	    input.onblur = null;
	
	    $(input).on("blur", function(event) {
	        delay(function() { onblur.call(input, event); }, 300);
	    });
	    // turn autocomplete of
	    $(this).attr('autocomplete','off');
	});

});

var delay = (function() {
    var timer = 0;

    return function(callback, timeout) {
        clearTimeout(timer);
        timer = setTimeout(callback, timeout);
    };
})();