DWR3.0实现异步上传文件

1.struts2-dwr-plugin-2.3.1.jar 

<servlet>
     <servlet-name>dwr</servlet-name>
       <servletclass>
          org.directwebremoting.servlet.DwrServlet
       </servlet-class>
    <init-param>
        <param-name>debug</param-name>
        <param-value>true</param-value>
     </init-param>
</servlet>
<servlet-mapping>
    <servlet-name>dwr</servlet-name>
    <url-pattern>/dwr/*</url-pattern>
</servlet-mapping>

<dwr>
    <allow>
    <!--creator="new"：表示每一次dwr请求但是创建一个新的实例
    javascript="DWRService"表示页面通过什么名字来对应调用你的java类提供服务 -->
    <create creator="new" javascript="DWRService">
    <!--指定为前台提供服务的java类   这里的DWRDemo类在页面使用的时候使用DWRService调用-->
    <param         name="class"value="net.farxiang.dwr.DWRUpload">          </param>        
    </create>
    </allow>
 </dwr>

<script type="text/javascript" src="/dwr/engine.js"></script>

<script type="text/javascript" src="/dwr/interface/DWRService.js"></script>

<script type="text/javascript" src="/dwr/util.js"></script>

<script type="text/javascript">
    var upload = function(){
        var headf = dwr.util.getValue("headfile"); 
         DWRService.headUp(headf,function(savePath){
            var div = document.getElementById("div");
            var img = document.createElement("img");
            img. savePath;
             img.id = "target";
            div.appendChild(img);
      });
    };
</srcipt>
<input type="file" name="headfile" id="headfile" onchange="upload();">
 <div id="div"></div>

package net.farxiang.dwr.DWRUpload;
import java.io.File;
import org.apache.commons.io.FileUtils;
import org.directwebremoting.WebContext;
import org.directwebremoting.WebContextFactory;
import org.directwebremoting.io.FileTransfer;
public class DWRUpload{
      
     public String headUp(FileTransfer ft){ 
           WebContext  wc = WebContextFactory.get(); 
           //获得应用路径
           String headImages = wc.getSession().getServletContext().getRealPath("/p_w_picpaths"); 
            File file = new File(headImages); 
            //如果文件夹不存在，就创建
          if( !file.exists()){ 
             file.mkdirs(); 
          } 
            try{ 
            //文件上传核心代码使用 commons-io-2.0.1.jar完成
            String[] fileNameSplit = ft.getFilename().split("\\\\");
            String fileName = fileNameSplit[fileNameSplit.length-1];
       FileUtils.copyInputStreamToFile(ft.getInputStream(), new File(headImages+File.separator+fileName));
             return headImages+File.separator+fileName;
            }catch(Exception e){ 
             e.printStackTrace(); 
            } 
          return null;
     }
}