（我是新手）web网页下载，在创建输入流时抛出异常

 1 protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 2         //获取文件名
 3         String fileName=req.getParameter("fileName");
 4         //获取文件后缀名
 5         String str=fileName.substring(fileName.lastIndexOf("."));
 6         //设置响应头,
 7         resp.setHeader("Content-Disposition","attachment; filename="+
 8                         System.currentTimeMillis()+str);
 9         //获得绝对路径
10         String path=this.getServletContext().getRealPath(fileName);
11         
12         InputStream in=null;
13         ServletOutputStream serOut=null;
14         try{
15             //创建文件
16         File file=new File(path);
17         in=new FileInputStream(file);
18         serOut=resp.getOutputStream();
19         
20         byte[] by=new byte[1024];
21         int len;
22         while((len=in.read(by))!=-1){
23             serOut.write(by, 0, by.length);
24         }
25         }catch(Exception e){
26             
27         }finally {
28             if(serOut!=null){
29                 serOut.close();
30             }
31             if (in!=null) {
32                 in.close();
33             }
34         }
35         
36         
37     }