用flash builder4.0+javaee做的多文件上传的小例子，关于环境配置就不多讲了，这个可以百度google一下，应该一大把。

界面大致如下：

源码：FlexMutifileUpload.mxml

<?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/mx"
			   creationComplete="application1_creationCompleteHandler(event)" 
			   minWidth="955" minHeight="600">
	<fx:Script>
		<![CDATA[
			import mx.collections.ArrayCollection;
			import mx.controls.Alert;
			import mx.core.FlexGlobals;
			import mx.events.FlexEvent;
			import mx.formatters.DateFormatter;
			import mx.utils.URLUtil;
			private var fileRefList:FileReferenceList=new FileReferenceList();
			
			public var fileAC:ArrayCollection=new ArrayCollection();
			public var tempAC:ArrayCollection=new ArrayCollection();
			
			private var date_ext:String="";
			private var request:URLRequest;
			
		//	public var serverName:String=URLUtil.getServerName(FlexGlobals.topLevelApplication.url);
	    //		public var serverPort:int=URLUtil.getPort(FlexGlobals.topLevelApplication.url);
			
			
			protected function application1_creationCompleteHandler(event:FlexEvent):void
			{
				// TODO Auto-generated method stub
				fileRefList.addEventListener(Event.SELECT,fileSelectedHandler);
			}
			
			protected function fileSelectedHandler(event:Event):void
			{
				for(var i:int=0;i<fileRefList.fileList.length;i++)
				{
					var fileRef:FileReference=FileReference(fileRefList.fileList[i]);
					var obj:Object=new Object();
					obj.fileRefrence=fileRef;//将进度条信息绑定
					obj.fileName=fileRef.name;//文件名称
					obj.fileType=fileRef.type;//文件类型
					obj.fileSize=(fileRef.size/1024).toFixed(2)+"KB";//四舍五入到小数点后两位
					this.txtUploadImg.text=fileRef.name;
					fileAC.addItem(obj);
					tempAC.addItem(obj);
				}
				this.dgFiles.dataProvider=fileAC;
			}
			protected function btnBrowse_clickHandler(event:MouseEvent):void
			{
				// TODO Auto-generated method stub
				var imgArray:Array=[];
				imgArray.push(new FileFilter("图片(*.jpg,*.png,*.bmp)","*.jpg;*.png;*.bmp"));
				fileRefList.browse(imgArray);
			}


			protected function btnUpload_clickHandler(event:MouseEvent):void
			{
				// TODO Auto-generated method stub
				for(var i:int=0;i<fileAC.length;i++)
				{
					var fileRef:FileReference=FileReference(fileAC[i]['fileRefrence']); 
					var url:String=encodeURI(URLUtil.getFullURL(FlexGlobals.topLevelApplication.url,"/")+"FlexMutifileUpload/FileUpload");
					request=new URLRequest(url);
					try
					{
						fileRef.upload(request,fileRef.name);
					}catch(er:Error)
					{
						Alert.show("上传文件出错！"+er.message);
					}
				}
			}
			public function deleteFileFromDG(event:MouseEvent):void
			{
			     var id:int=this.dgFiles.selectedIndex;
				 fileAC.removeItemAt(id);
				 fileAC.refresh();
			}
			

		]]>
	</fx:Script>
	<fx:Declarations>
		<!-- 将非可视元素（例如服务、值对象）放在此处 -->
	</fx:Declarations>
	<s:BorderContainer horizontalCenter="0" verticalCenter="6" borderVisible="false" borderWeight="0"  width="646" height="377">
	
	<mx:DataGrid id="dgFiles" horizontalCenter="-55" verticalCenter="-9" height="281" width="514">
		<mx:columns>
			<mx:DataGridColumn headerText="文件名" dataField="fileName"/>
			<mx:DataGridColumn headerText="类型" dataField="fileType"/>
			<mx:DataGridColumn headerText="大小" dataField="fileSize"/>
			<mx:DataGridColumn headerText="操作" width="300">
				<mx:itemRenderer>
					<fx:Component>
						<mx:HBox width="100%" height="100%" >
							<mx:ProgressBar id="myProgressbar" minimum="0" maximum="100" 
								 width="150" height="90%"	labelPlacement="center"  source="{data.fileRefrence}" />
							<s:Button label="删除" click="outerDocument.deleteFileFromDG(event)"  />
						</mx:HBox>
					</fx:Component>
				</mx:itemRenderer>
			</mx:DataGridColumn>
		</mx:columns>
	</mx:DataGrid>
	<s:TextInput id="txtUploadImg" x="10" y="343" width="225" editable="false"/>
	<s:Button id="btnBrowse" x="271" y="344" label="浏览"  click="btnBrowse_clickHandler(event)"  width="125"/>
	<s:Button id="btnUpload" x="400" y="344" label="上传" click="btnUpload_clickHandler(event)"  width="110"/>
	</s:BorderContainer>
</s:Application>

后台是基于java servlet实现的，下面是FileUpload.java文件

package com.coderloft.util;

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Iterator;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

/**
 * Servlet implementation class FileUpload
 */
public class FileUpload extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
	//定义文件保存路径
	private String savePath="d:\\upload\\";
	
	// 限制文件的上传大小
	private int maxPostSize = 100 * 1024 * 1024;
    /**
     * @see HttpServlet#HttpServlet()
     */
    public FileUpload() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setCharacterEncoding("UTF-8");
		response.setContentType("text/html;charset=UTF-8");
		processRequest(request,response);
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setCharacterEncoding("UTF-8");
		response.setContentType("text/html;charset=UTF-8");
		processRequest(request,response);
	}
	protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		
	    PrintWriter out=response.getWriter();
	    //获取服务器上路径位置
	    String fileRename = request.getParameter("filename");
	    String path=getServletContext().getRealPath("\\uploadfile");
	   
	    //判断文件是否存在
	    File file=new File(path);
	    if(!file.exists()){
	    	boolean createSuccess=file.mkdirs();
	    	if(!createSuccess){
	    		System.out.println("文件创建失败，不能上传");
	    		return;
	    	}
	    }
	    //保存文件到服务器中
	    DiskFileItemFactory factory=new DiskFileItemFactory();
	    factory.setSizeThreshold(4096);//设置缓存大小
	    ServletFileUpload upload=new ServletFileUpload(factory);
	    upload.setHeaderEncoding("UTF-8");
	    upload.setSizeMax(maxPostSize);
	    try{
	    	List fileItems=upload.parseRequest(request);
	    	Iterator iter=fileItems.iterator();
	    	while(iter.hasNext()){
	    		FileItem item=(FileItem) iter.next();
	    		if(!item.isFormField()){
	    		 
	    			String name=item.getName();
	    			if (fileRename != null && fileRename.length() > 0) {
						name = fileRename;
					}
					try {
						item.write(new File(path +"\\"+ name));
						System.out.println("上传成功：" + path);
					} catch (Exception e) {
						e.printStackTrace();
					}
	    		}
	    	}
	    }catch(Exception ex){
	    	ex.printStackTrace();
	    } 
	}
}

关于文件上传，在这里多说一句：

文件上传时，考虑到中文路径的问题，试着在你的浏览器中输入一个中文路径，看浏览器是否使用的是UTF-8的编码格式，如果浏览器编码正确，那么要上传文件时，在flex端将字符encodeURI一下，看看你的tomcat服务器编码是否修改为UTF-8,修改方法是：找到tomcat安装目录下的,我的目录是：D:\Program Files\apache-tomcat-6.0.16\conf

conf/server.xml,找到<Connector节点 添加 URIEncoding="utf-8",

去下载源码