Flex HttpService 传值

Flex中如何利用HTTPService的send()，将参数传递给HTTPService

<?xml version="1.0" encoding="utf-8"?> 
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" 
        layout="vertical" 
        verticalAlign="middle" 
        backgroundColor="white"> 
  
    <mx:Script> 
        <![CDATA[ 
            import mx.controls.Alert; 
            import mx.events.ValidationResultEvent; 
            import mx.utils.StringUtil; 
  
            private function submit_click(evt:MouseEvent):void { 
                var result:ValidationResultEvent = stringValidator.validate(); 
                var params:Object = {}; 
  
                lbl.text = ""; 
  
                switch (result.type) { 
                    case ValidationResultEvent.INVALID: 
                        Alert.show(result.message, result.type); 
                        break; 
                    case ValidationResultEvent.VALID: 
                        params["name"] = StringUtil.trim(firstName.text); 
                        httpServ.send(params); 
                        break; 
                } 
            } 
        ]]> 
    </mx:Script> 
  
    <mx:StringValidator id="stringValidator" 
            source="{firstName}" 
            property="text" 
            minLength="2" 
            maxLength="{firstName.maxChars}" /> 
  
    <mx:HTTPService id="httpServ"> 
        <mx:resultFormat>flashvars</mx:resultFormat> 
        <mx:url>http://www.flash-mx.com/mm/greeting.cfm</mx:url> 
        <mx:result>lbl.text = httpServ.lastResult.welcomeMessage;</mx:result> 
        <mx:fault>Alert.show(event.toString(), event.type);</mx:fault> 
    </mx:HTTPService> 
  
    <mx:ApplicationControlBar dock="true"> 
        <mx:Form> 
            <mx:FormItem label="Name:" required="true" 
                    direction="horizontal"> 
                <mx:TextInput id="firstName" 
                    maxChars="20" /> 
                <mx:Button label="Submit" 
                        click="submit_click(event);" /> 
            </mx:FormItem> 
        </mx:Form> 
    </mx:ApplicationControlBar> 
  
    <mx:Label id="lbl" fontSize="32" /> 
  
</mx:Application>