struts2的action以流的方式实现文件下载时的问题

public class ExportExcelInfo extends BaseAction {
    private String filename;
    @SuppressWarnings("unused")
    
    private static final long serialVersionUID = 1L;
    private static final LogDebug logDebug = new LogDebug(ExportExcelInfo.class);
    public String getfilename() {
        return filename;
    }
    public void setfilename(String filename) {
        this.filename = filename;
    }
 
    public String  execute() throws Exception{
         this.getResponse().setContentType("application/vnd.ms-excel");    
         this.getResponse().setHeader("Content-disposition", "attachment;filename=a.xls");
        this.filename="\\template\\a.xls";
        String filePath=this.getRequest().getRealPath(this.filename);
        byte[] buffer = new byte[16*1024];
        int read;
        File file = new File(filePath);
        InputStream is = new FileInputStream(file);
        OutputStream os = this.getResponse().getOutputStream();
        while((read = is.read(buffer))>=0){
            System.out.println("read:"+read);
            os.write(buffer,0,read);
            os.flush();
        }
        os.close();
        is.close();
        return null;
    }

}

千万注意，在上面的输出流，必须用 this.getResponse.getOutPutStream才行，不然将无法把服务器端的文件下载到本地