Uploadify上传onComplete事件有关问题

 
 onComplete: function (event, queueID, fileObj, response, data) { 
 				alert(response);//此处得到结果为   {"message","上传OK"} 
 				alert(response.message);// 此处是null....为什么 
 			   　   alert("文件:" + fileObj.name + "上传成功"); 
 			   　} 
 

public class UpLoadAction extends ActionSupport{
    private File file;
    private String fileFileName;
    private String message;
    public String getMessage() {
        return message;
    }
    public void setMessage(String message) {
        this.message = message;
    }
    public String execute(){
        System.out.println("文件名是"+fileFileName+file);
        String root=ServletActionContext.getServletContext().getRealPath("/upload");
        try {
            byte[]b=new byte[1024];
            int length;
            InputStream read=new FileInputStream(file);
            OutputStream write=new FileOutputStream(new File(root,fileFileName));//文件名保存为例 
            while((length=read.read(b))!=-1){
                write.write(b, 0, length);
            }
            read.close();
            write.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        message="我是服务器";
        return SUCCESS;
    }
    public void setFile(File file) {
        this.file = file;
    }

    public void setFileFileName(String fileFileName) {
        this.fileFileName = fileFileName;
    }
}