Flex通过HTTPService与servlet通信

flex代码：
<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/halo" minWidth="1024" minHeight="768">
<fx:Script>
<!--[CDATA[
import mx.controls.*;
import mx.rpc.events.ResultEvent;
import mx.rpc.http.mxml.HTTPService;

protected function button1_clickHandler(event:MouseEvent):void
{
var addNew:HTTPService = new HTTPService();
addNew.resultFormat = "text" ;
addNew.method = "POST";
addNew.url = "http://localhost:8084/Flex_web/flex";
addNew.addEventListener(ResultEvent.RESULT,result_Handler);

var param:Object = new Object();
param.user = user.text;
param.pwd = pwd.text;

addNew.send(param);
}

public function result_Handler(event:ResultEvent):void
{
var mes:String = event.message.body.toString();
Alert.show("成功！" + mes,"信息");
}
]]-->
</fx:Script>
<fx:Declarations>
<!-- Place non-visual elements (e.g., services, value objects) here -->
</fx:Declarations>
<s:Panel x="200" y="110" width="224" height="157" title="登录系统">
<s:Button x="24" y="92" label="登录" click="button1_clickHandler(event)" width="171" focusEnabled="true"/>
<s:TextInput x="67" y="10" id="user"/>
<s:TextInput x="67" y="49" id="pwd"/>
<s:Label x="20" y="15" text="用户名："/>
<s:Label x="20" y="55" text="密码："/>
</s:Panel>
</s:Application>
servlet代码：
package advang;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class flexServlet extends HttpServlet {

protected void processRequest(HttpServletRequest request, Htt