java 实现对指定目录的文件进行下载

@RequestMapping("/exportDocument")
    @ResponseBody
    public void exportDocument(HttpServletRequest request,HttpServletResponse response) throws IOException {    
        XWPFDocument xdoc = null;
        FileInputStream is = null;
        OutputStream out=null; 
        try {
            String wordName="数聚空港2.0使用手册.docx";
            wordName = new String(wordName.getBytes(), "iso8859-1");
           // File file = new File("/root/usersGuide.docx"); 
            response.setContentType("APPLICATION/OCTET-STREAM");
            response.setHeader("Content-Disposition", "attachment; filename="
                    + wordName);
            is = new FileInputStream("/root/usersGuide.docx");
            out=response.getOutputStream();//获得一个output对象
            xdoc = new XWPFDocument(is);
            } catch (IOException e) {
                e.printStackTrace();
            }finally{
                try {
                    xdoc.write(out);//Write out this document to an Outputstream.
                    is.close();
                    out.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
                 /*上述是都word文档的下载*/


                /*下面是对各种类型的文件下载*/
        
                 /*//2.获取要下载的文件名
                String fileName = "test.png";
                 //3.设置content-disposition响应头控制浏览器以下载的形式打开文件
                 response.setHeader("content-disposition", "attachment;filename="+fileName);
                //4.获取要下载的文件输入流
                InputStream in=null;
                OutputStream out=null;
                try {//获取要下载的文件的绝对路径
                    in=new FileInputStream("/root/运营线路图0.3.5版.png");
                    int len = 0;
                     //5.创建数据缓冲区
                     byte[] buffer = new byte[1024];
                     //6.通过response对象获取OutputStream流
                     out = response.getOutputStream();
                     //7.将FileInputStream流写入到buffer缓冲区
                     while ((len = in.read(buffer)) > 0) {//in.read(byte[] b)最多读入b.length个字节 在碰到流的结尾时 返回-1
                     //8.使用OutputStream将缓冲区的数据输出到客户端浏览器
                         out.write(buffer,0,len);
                     }
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                }finally{
                     in.close();
                     out.close();
                }*/
                 
    }