通過url實現檔案下載

@Log("下載檔案")
@ResponseBody
@RequestMapping(value = "/download", method = RequestMethod.GET)
public R Download(HttpServletResponse response,Long id) {
    String fileUrl = fileService.get(id).getUrl();//檔案url
    String fileName = fileUrl.substring(fileUrl.lastIndexOf("/")+1);//檔名字

    response.setHeader("content-type", "application/octet-stream");
    response.setContentType("application/octet-stream");
    response.setHeader("Content-Disposition", "attachment;filename=" + fileName);

    byte[] buff = new byte[1024];
    BufferedInputStream bis = null;
    OutputStream os = null;

    try {
        os = response.getOutputStream();
        bis = new BufferedInputStream(new URL(fileUrl).openConnection().getInputStream());
        int i = bis.read(buff);
        while (i != -1) {
            os.write(buff, 0, buff.length);
            os.flush();
            i = bis.read(buff);
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (bis != null) {
            try {
                bis.close();
                return R.ok();
            } catch (IOException e) {
                e.printStackTrace();
                return R.error();
            }
        }
    }
    return null;
}

R工具類：

import java.util.HashMap;
import java.util.Map;

public class R extends HashMap<String, Object> {
   private static final long serialVersionUID = 1L;

   public R() {
      put("code", 0);
      put("msg", "操作成功");
   }

   public static R error() {
      return error(1, "操作失敗");
   }

   public static R error(String msg) {
      return error(500, msg);
   }

   public static R error(int code, String msg) {
      R r = new R();
      r.put("code", code);
      r.put("msg", msg);
      return r;
   }

   public static R ok(String msg) {
      R r = new R();
      r.put("msg", msg);
      return r;
   }

   public static R ok(Map<String, Object> map) {
      R r = new R();
      r.putAll(map);
      return r;
   }

   public static R ok() {
      return new R();
   }

   @Override
   public R put(String key, Object value) {
      super.put(key, value);
      return this;
   }
}