Learning JSF2: Ajax in JSF – using f:ajax tag

This is a third post in Learning JSF 2 series. The first one on Managed Beans can be found here and second one on navigation can be found here

As you probably know JSF 2 is a major upgrade over JSF 1.2. One of the major additions to this version of JSF is standard Ajax support. This article covers Ajax features in JSF 2. If you are familiar with RichFaces and specifically the a4j:support tag then learning how to use Ajax features in JSF 2 is going to be very easy. Many concepts and features are being carried over from RichFaces.  Let’s start. 

JSF 2 comes with one tag that provides Ajax functionality. The tag is called f:ajax (sounds familiar to a4j:support – right?) When I do RichFaces trainings, I like to divide the core ideas into three parts: sending an Ajax request, partial view rendering and partial view processing. I will use the same approach here. 

Sending an Ajax request

JSF comes with one tag to send an Ajax request, the tag is called f:ajax. This tag is actually a client side behavior (here is a great post by Andy Schwartz on JSF 2 client behaviors). Being a behavior implies it’s never just used by itself on a page, it is always added as a child tag (behavior) to another UI component (or can even wrap several components). Let’s use a small echo application to demonstrate usage of this tag. 

<h:form> 
   <h:panelGrid> 
      <h:inputText value="#{bean.text}" > 
         <f:ajax event="keyup"/> 
      </h:inputText> 
      <h:outputText id="text" value="#{bean.text}" /> 
   </h:panelGrid> 
</h:form>

Code snippet above takes care of firing an Ajax request based on onkeyup event. Notice the actual event name is keyup. This takes care of firing an Ajax request. Next we need to figure out how to do partial view rendering. 

Attribute Description
event String on which event Ajax request will be fired. If not specified, a default behavior based on parent component will be applied. The default event is action for ActionSource (ie: button) components and valueChange for EditableValueHolder components (ie: input). action and valueChange are actual String values that can be applied applied event attribute. 

HTML Tables

Note: In RichFaces 3.x, you specify the event with onevent, for example onkeyp. In JSF 2, you only specify the actual action: keyup.

Partial view rendering

With JSF 1.2 (and without RichFaces) every request would render the entire view back to us. That was simple, we didn’t have to worry which parts of the JSF view we want to be updated. Of course the basic concept behind Ajax is to only update those parts of the page that we actually need to. In order to accomplish this, we should only render those components on the server whose markup we want to update in browser. What all this means is we now need to specify which components in JSF view we want to render back. Partial view is still rendered on the server. Some updated portion is sent as XML to the browser where the DOM is updated.  Our example is rather simple, there is just one component with id text. f:ajax tag has render attribute which points to id’s of components to be rendered (or rerendered) back. It could also take an EL expression. Adding it to our example, it looks like this:

<h:form> 
   <h:panelGrid> 
      <h:inputText value="#{bean.text}" > 
         <f:ajax event="keyup" render="text"/> 
      </h:inputText> 
      <h:outputText id="text" value="#{bean.text}" /> 
   </h:panelGrid> 
</h:form>

If you have been using RichFaces, than the same attribute in RichFaces is called reRender. The event that is specified via event attribute must be an event that the parent component supports. If you look at the generated HTML, you will see something like this:

<input id="j_idt5:j_idt7" type="text" name="j_idt5:j_idt7" 
   onkeyup="mojarra.ab(this,event,'keyup',0,'j_idt5:text')" />

If you specify an event that is not available on the parent component, an error message will be displayed when you run the page. 

That’s it. Here is the bean code in case you want to run this page:

@ManagedBean(name = "bean") 
public class Bean { 
   private String text; // getter and setter 
   ... 
}

Let’s say we also want to show and update a counter that shows the length of a string we entered. Adding new property to bean:

private Integer count; // getter and setter

Also adding Ajax listener to do the counting, notice that method takes a new AjaxBehaviorEvent object: 

public void countListener(AjaxBehaviorEvent event) { 
   count = text.length(); 
}
Attribute Description
listener Listener method to invoke during Ajax request. 

Updating the page:

<h:form> 
   <h:panelGrid> 
      <h:inputText value="#{bean.text}" > 
         <f:ajax event="keyup" render="text count" listener="#{bean.countListener}"/> 
      </h:inputText> 
      <h:outputText id="text" value="#{bean.text}" /> 
      <h:outputText id="count" value="#{bean.count}" /> 
   </h:panelGrid> 
</h:form>

Notice that we added count id to render attribute. You use space as a separator for id’s. 

In our examples above we actually specified on which even to fire an Ajax request. As it turns out we don’t have to specify an event. If we don’t specify one, each UI component has a default event on which Ajax request would be send. Taking h:inputText, the default Ajax event is onchange. Our example would almost work however, instead of onkeyup, you would now have to tab out or click outside the input field to fire the Ajax request:  So, we could have written our example like this (without event attribute):

<h:inputText value="#{bean.text}" > 
   <f:ajax render="text count" listener="#{bean.countListener}"/> 
</h:inputText>
Attribute Description
render Determines id’s of components to be rendered. 
 

In our example, render pointed to actual component id we want to render back. render attribute could be set to the following values: 

Possible values for render attribute Description
@all Render all components in view
@none Render no components in view (this is also the default value if render is not specified)
@this Render only this component, the component that triggered the Ajax request
@form Render all components within this form (from which Ajax request was fired)
id’s One or more id’s of components to be rendered
EL EL expression which resolves to Collection of Strings

render could also point to EL expression. In this case it’s possible to determine which components to render in run time. Here is how it works when using EL:

  • You bind render=”#{bean.renderComponents}”. Initial page is rendered. #{bean.renderComponents} is resolved during page rendering, for example to id’s compId1 and compId2.
  • On next Ajax request, compId1 and compId2 will be rerendered. During this request, #{bean.renderComponents} could be changed in runtime. For example, it is now set to compId3 and compId4. You also have to remember to rerender this control (in order to update the ids)
  • Page is rendered (from step 3). Values of compId3 and compId4 are now present (rendered) in the page.
  • On next Ajax request, components with id’s compId3 and compId4 will be rerendered.

Note: this behavior is slightly different than what you get do in RichFaces 3. In RichFaces reRender attribute when bound to an EL expression is resolved in the current request. 

It’s also possible to issue Ajax requests programmatically using the jsf.ajax.request() JavaScript API: 

<h:head> 
   <h:outputScript name="jsf.js" library="javax.faces"/> 
</h:head> 
... 
<h:body>
   <h:form id="form"> 
      <h:inputText value="#{bean.text}" 
           onkeyup="jsf.ajax.request(this, event, {render:'form:text'});"/> 
      <h:outputText id="text" value="#{bean.text}" /> 
   <h:form>
</h:body>

A few things to look for. First, you need to include jsf.js file which provides all the JavaScript functionality. Second, for render you need to use client id (not just component id). 

Let’s look at an example using a button: 

<h:form> 
    <h:panelGrid > 
    <h:commandButton value="Get time" > 
      <f:ajax event="click" render="time"/> 
    </h:commandButton> 
    <h:outputText value="#{bean.now}" id="time"/> 
</h:panelGrid> 
</h:form>

Java bean:

public class Bean {
   public Date getNow () {
      return (new Date());
   }
}

In example above, we are adding Ajax behavior to standard JSF button. We specified both event and render. But, the example could also be rewritten like this: 

<h:form> 
    <h:panelGrid > 
    <h:commandButton value="Get time" > 
      <f:ajax render="time"/> 
    </h:commandButton> 
    <h:outputText value="#{bean.now}" id="time"/> 
</h:panelGrid> 
</h:form>

So far we covered sending an Ajax request and partial view rendering. Let’s now cover the third part: partial view processing. 

Partial view processing

In JSF 1.x (and without RichFaces) when a form was submitted, the entire form was processed on the server. Processed means that all components went through phases Apply Request Values, Process Validation and Update Model. When Ajax, there are situations when you don’t want to process all the components in the form. To control which components will get processed, we use execute attribute on f:ajax tag. 

<h:commandButton value="Click" > 
  <f:ajax execute="@form" render="time"/> 
</h:commandButton>

In above example, when button is clicked an Ajax request is fired and the entire form will be processed on the server. 

Attribute Description
execute Determines id’s of components to be processed on server
 
Possible values for execute attribute Description
@all Process all components in view
@none Process no components
@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)

id’s Implicit id’s of components to be processed, space separated
EL Must resolve to Collection of Strings

More examples

Let’s look at more examples using f:ajax tag. 

If you have multiple controls that fire an Ajax request you could next f:ajax inside each one. Alternatively, you can also put f:ajax around those controls:

<f:ajax> 
  <h:panelGrid>   
    <h:selectBooleanCheckbox> 
    <h:inputText> 
    <h:commandButton> 
  </h:panelGrid> 
</f:ajax>  

From example above, f:ajax will be added to each control using their default Ajax events:

h:panelGrid no default behavior, so no Ajax event will be added
h:selectBooleanCheckbox onchange
 
h:inputText onchange
 
h:commandButton onclick
 

We can also specify an event which would then be applied to children components: 

<f:ajax event="click"> 
  <h:panelGrid>   
    <h:selectBooleanCheckbox> 
    <h:inputText> 
    <h:commandButton> 
     <f:ajax event="focus"/> 
    </h:commanButton> 
  </h:panelGrid> 
</f:ajax>  

In example above, onclick event will be added to panelGrid, inputText and commandButton. commandButton would also have onfocus event applied to it. 

<f:ajax event="valueChange"> 
  <h:panelGrid>   
    <h:selectBooleanCheckbox> 
    <h:inputText> 
    <h:commandButton> 
     <f:ajax event="focus"/> 
    </h:commanButton> 
  </h:panelGrid> 
</f:ajax>

In example above we are applying the default valueChange event. It’s not possible to apply valueChange to panelGrid, so nothing will be applied to it. h:selectBooleanCheckbox and h:inputText will have valueChange applied to both. As valueChange is not a valid event for h:commanButton, the event will not be applied and h:commandButton will have only onfocus applied to it. 

Hopefully this gives you a good introduction how to use f:ajax tag in JSF 2. 

RichFaces

If you have been using RichFaces and specifically a4j:support tag then you might be wondering what’s going to happen to it? In RichFaces 4 (JSF 2 based) a4j:support is going to be renamed to a4j:ajax to match the standard tag name. a4j:ajax will use the standard f:ajax under the covers but will also provide numerous advanced features and attributes that you get today in RichFaces and which are not available in JSF 2. You will also have tags such as a4j:poll, a4j:jsFunction, a4j:outputPanel which are not available in JSF 2 and which give you more power and flexibility. 

I want to thank Nick Belaevski from RichFaces team (Exadel) for doing technical review for this article.

75 comments

  1. andy

    but it’s just defined:
    if you look at the migration guide (http://community.jboss.org/wiki/RichFacesMigrationGuide33x-4xMigration-ComponentsMigration-A4jComponents): a4j:ajax is corresponding to a4j:support!
    and the a4j:jsFunction is just for requesting new data:
    The component performs Ajax requests directly from JavaScript code and retrieves server-side data. The server-side data is returned in JavaScript Object Notation (JSON) format prior to the execution of any JavaScript code defined using the oncomplete attribute.
    If you’d like to submit something, you must use a4j:param-Tags for the a4j:jsFunction. But it’s not comfortable!!!

    So now, it’s the same Problem: What’s the alternative for the a4j:support-tag? or: how an action-Attribute could be added to an a4j:ajax-Tag?

  2. andy

    if I use

    a4j:ajax event=”change” render=”showTest” oncomplete=”sendAJAX_TEST()” />

    andy

    a4j:jsFunction name=”sendAJAX_TEST” action=”AJAX_TEST” render=”showTest” />

    it works, but with TWO ajax-Requests, which aren’t with performance!

  3. max

    @andy: a4j:jsFunctions sends the same request as a4j:ajax but from a JavaScript function: “The component performs Ajax requests directly from JavaScript code..”. This post describes how a4j:jsFunction works: http://goo.gl/RKBLM

  4. andy

    Thanks! I’ve read the link and test it in my application, but it doesn’t work! So I’ve checked out the webflow-richfaces-showcase-project from the spring-svn (https://src.springframework.org/svn/spring-samples) and adapt it to RF4 and SWF 2.3.0. Than I’ve modified step1 in “Popup With State Transition” to test the case shown in your link (http://goo.gl/RKBLM) but it doesn’t work! Here is the modified project, so you can download it on: http://www.file-upload.net/download-3490981/webflow-richfaces-showcase.rar.html
    So is it a RF4-bug?

  5. max

    @andy: I don’t know whether it’s a bug in RichFaces or maybe Spring. Just trying probably won’t tell you where the bug is, this may require real debugging. However, you can try and narrow down the issue.

    - Does it work with just h:commandButton (no Ajax)?
    - Does it work with h:commandButton and f:ajax?
    - Does it work with a4j:commandButton?
    - Does it work with a4j:jsFunction?

  6. David

    Congratulations for the post!
    I have a doubt about the client update mechanism, when using the render attribute, it renders all the markup, but in most of cases the markup is not modified, but tha value has changed.
    How can I change ONLY the value of some components after an ajax call?

    Thanks
    david

  7. David

    @max, for example in the code below as you are writing on the inputText the backing bean changes the “text” property and render the whole outputText component, with all the HTML markup (for example etc etc)
    But what you need is only the value, not the entire markup, so you could get the new value for the text comnponent and perform a text.setAttribute (“value”, text_new_value).

    Imagine an scenario where the component to update is a comboBox with 100 elements and after an ajax call we want to update its VALUE. Using the “render” attribute we’ll force to receive the 100 elements and rerender them, right?
    And we just need the new value.

    I hope this clarify my question

  8. max

    @David: You can do it with directly with JavaScript API. For example, call a JavaScript function in oncomplete callback to change only the value.

  9. David

    @max: Thank you max,
    This is how I’m doing it right now, but I wondered if there were another (automated) way of doing it.
    Thanks againg and best regards
    david

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  13. Jorge

    I follow your examples and make this script and didn’t work, can you help me what’s wrong? Thanks for all

    public class Bean2 {
    public String valor1;

    public Bean2() {
    }

    public String getValor1() {
    return valor1;
    }

    public void setValor1(String valor1) {
    this.valor1 = valor1;
    }
    }

  14. max

    @Jorge: what exactly didn’t work? Did you see any error messages? Did you use just JSF 2 or also RichFaces 4? Please link the page code via pastie.org.

  15. Jorge

    I follow your examples and make this script and didn’t work, can you help me what’s wrong? Thanks for all

    h:form>
    h:panelGrid columns=”1″>
    h:inputText value=”#{bean2.valor1}”/>
    h:commandButton value=”Type text” >
    f:ajax render=”texto2″/>
    /h:commandButton>
    h:outputText id=”texto2″ value=”#{bean2.valor1}” />
    /h:panelGrid>
    /h:form>



    public class Bean2 {
    public String valor1;

    public Bean2() {
    }

    public String getValor1() {
    return valor1;
    }

    public void setValor1(String valor1) {
    this.valor1 = valor1;
    }
    }

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