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luni, 13 iunie 2016

JSF 2.3 - Generating a JavaScript function in the global JavaScript scope which allows the end user to execute a JSF AJAX request by just a function call in the JavaScript context

Sometimes, it may be useful to encapsulate the AJAX requests in JavaScript functions placed in the JavaScript global scope in such way that we can simply call them by name, without arguments, or with arguments that represent the data that should be passed to the server‐side via the encapsulated AJAX request. Obviously the jsf.ajax.request() and mojarra.ab() functions donʹt allow us to accomplish that, but as you will see, JSF 2.3 (and OmniFaces) will call the jsf.ajax.request() from a JavaScript global scoped function that can be easily called by its name.

Letʹs take a look at this simple HTML code:

<h5>Your Feedback About JSF 2.3: </h5>
<div>
 Your Name: <input id="userId" type="text"/>
 <p id="feedbackId" contenteditable="true">type your feedback here</p>
</div>
<br/>
<button onclick="sendFeedback();">Send Feedback</button>

Note that the sendFeedback() function should be defined as a global scoped JavaScript function capable to fire an JSF AJAX request. The user name and feedback should be added as parameters of the AJAX request.

JSF 2.3 comes with a handy new component named CommandScript (starting with JSF 2.3.0-m06) which is capable to solve this kind of tasks. This component be used by the page authors via the <h:commandScript/> tag. This component extends the javax.faces.component.UICommand (<h:commandXxx/>) which means that it inherits the major features of JSF commands, like action, actionListener, immediate, etc. Moreover, this component also supports nesting of <f:param/>, <f:actionListener/> and <f:setPropertyActionListener/>, exactly as in <h:commandXxx/>.

In addition, the foundation of CommandScript consists of the fact that it can generate a JavaScript function in the global JavaScript scope. Via this function call, the end‐user can execute JSF AJAX requests. There are two requirements for this component:

- The name attribute is mandatory, and it indicates the name of the generated JavaScript function (you can define namespaced function name also by using a dot, ".", inside the function name).
- The <h:commandScript/> must be nested in a <h:form/>.

For example, the simplest way to use <h:commandScript/>, is listed below:

<h:form>
 <h:commandScript name="sendFeedback"/>
</h:form>

This example is correct, but is doesnʹt do much! Basically, it generates in page a snippet of code as below:

<span id="j_idt5:j_idt6">
 <script type="text/javascript">
  var sendFeedback=function(o){
   var o=(typeof o==='object')&&o?o:{};
   mojarra.ab('j_idt5:j_idt6',null,'action',0,0,{'params':o})
  }
 </script>
</span>

It is important to notice that this is just a simple JSF AJAX request, so when we call the sendFeedback() function, we will fire an ʺemptyʺ JSF AJAX request. Obviously, we are interested to control the values of the execute and render attributes. This is very simple, because <h:commandScript/> supports the execute and render attributes exactly as <f:ajax/>, so we can do this:

<h:form>
 <h:commandScript name="sendFeedback" execute="@form" render=":savedId"/>
</h:form>

Now, the generated code becomes:

<span id="j_idt5:j_idt6">
 <script type="text/javascript">
  var sendFeedback=function(o){
   var o=(typeof o==='object')&&o?o:{};
   mojarra.ab('j_idt5:j_idt6',null,'action','@form','savedId',{'params':o})
  }
 </script>
</span>

With just a snap of a finger we can add the action:

<h:form>
<h:commandScript name="sendFeedback" execute="@form"
                 render=":savedId" action="#{feedbackBean.send()}"/>
</h:form>

So far, so good! If you donʹt have extra information to pass to the server‐side, or it is collected from the form (e.g. <h:inputText/>), then this should be enough. But, in our case we have extra information to pass and this information comes through plain HTML code, so we have to find a solution for adding this information into the JSF AJAX request. Thanks to the <h:commandScript/> the generated function also supports a JavaScript object as an argument which will then end up in the HTTP request parameter map (donʹt forget about <f:param/>). In order to pass an object to the generated function, we need to wrap its call into a global JavaScript function, as below:

<h:outputScript>
 function sendFeedbackWrapper(){
  sendFeedback({user: document.getElementById("userId").value,
  feedback: document.getElementById("feedbackId").innerHTML });
 }
</h:outputScript>

And modify the button as:

<button onclick="sendFeedbackWrapper();">Send Feedback</button>

On the server‐side, the passed information can be easily extracted via the OmniFaces Faces#getRequestParameter() utility method:

String user = Faces.getRequestParameter("user"); // user
String feedback = Faces.getRequestParameter("feedback"); // feedback

Or, we can use the JSF pure solution:

Map<String, String> params = FacesContext.getCurrentInstance().
                                  getExternalContext().getRequestParameterMap();
       
String user = params.get("user"); // user
String feedback = params.get("feedback"); // feedback

The complete application is available here. The application was tested under Payara 4 with JSF 2.3.0-m06.

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