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对于getOutputStream()，api里是这样说的：Either this method or getWriter()

may be called to write the body, not both.

也就是getOutputStream()和getWriter() 只能使用一个，把代码里的response.getOutputStream()全部删之后，统一使用response.getWriter() 作为输出流，问题解决。

全部代码如下:

response.setContentType( "application/octet-stream ");
        response.addHeader("Content-Disposition","attachment;filename=" + "work.xls");
        java.io.FileInputStream fileInputStream = null;
        ServletOutputStream sos = null;
        PrintWriter writer = null;
        try
        {
            fileInputStream = new java.io.FileInputStream(file);
            writer = response.getWriter();
            response.getOutputStream();
            int i;
            while((i = fileInputStream.read()) != -1)
            {
                writer.write(i);
            }
            writer.flush();
        }
        catch (FileNotFoundException e)
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        catch (IOException e)
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        finally
        {
            if(sos != null)
            {
                try
                {
                    sos.close();
                }
                catch(IOException e)
                {
                    e.printStackTrace();
                }
            }
            if(fileInputStream != null)
            {
                try
                {
                    fileInputStream.close();
                }
                catch(IOException e)
                {
                    e.printStackTrace();
                }
            }
            if(writer != null)
            {
                writer.close();
            }
        }

http://blog.csdn.net/yuzhongzhu/article/details/6290526