DownLoad文件

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

//Content-Disposition ： 保存文件时设置的头信息
//Windows-31J ： windows的标准字符集
//ISO-8859-1  :  编码格式
//为了防止文件名中出现中文，发生乱码
response.setHeader("Content-Disposition", 
                   "attachment; filename=" + new String(fileName.getBytes("Windows-31J"), "ISO-8859-1"));

InputStream  in  = new FileInputStream(filePath);
OutputStream out = response.getOutputStream();
byte[] buff = new byte[1024];
int len = 0;
while ((len = in.read(buff, 0, buff.length)) != -1) {
    out.write(buff, 0, len);
}

in.close();
out.close();