@RequestMapping("download")

    public void download(HttpServletRequest request,HttpServletResponse response){

        BufferedInputStream dis = null;

        BufferedOutputStream fos = null;

        String urlString = request.getParameter("urlString");

        String fileName = urlString.substring(urlString.lastIndexOf('/') + 1);

        try {

            URL url = new URL(urlString);

            //response.setContentType("application/x-msdownload;");

            response.setContentType("application/octet-stream");

            response.setHeader("Content-disposition", "attachment; filename=" + new String(fileName.getBytes("utf-8"), "ISO8859-1"));

            response.setHeader("Content-Length", String.valueOf(url.openConnection().getContentLength()));

            dis = new BufferedInputStream(url.openStream());

            fos = new BufferedOutputStream(response.getOutputStream());

            byte[] buff = new byte[2048];

            int bytesRead;

            while (-1 != (bytesRead = dis.read(buff, 0, buff.length))) {

                fos.write(buff, 0, bytesRead);

            }

        } catch (Exception e) {

            e.printStackTrace();

        } finally {

            if (dis != null)

                try{

                    dis.close();

                }catch (Exception e){

                    e.printStackTrace();

                }

            if (fos != null)

                try{

                    fos.close();

                }catch (Exception e){

                    e.printStackTrace();

                }

        }

    }

<input type="button" onclick="downloadImage()" value="下载">

<script>

   function downloadImage(){

       var urlString = "http://pic32.nipic.com/20130829/12906030_124355855000_2.png";

       //跳转到后端控制器

       location.href="${ctx}/guest/download.do?urlString="+urlString;

   }

</script>