servlet实现文件的下载

public class DownLoadServlet extends HttpServlet{
public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
this.doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {

FileInputStream fis=null;
request.setCharacterEncoding("UTF-8");


         String fileName = request.getParameter("fileName"); //获取文件名
try{
ServletContext servletContext=this.getServletContext();
         String realpath = servletContext.getRealPath("/templates/"); //获取服务器的物理路径
String templateXlsPath = realpath + File.separator + fileName;//获取完整的文件路径

//读取模板
fis = new FileInputStream(templateXlsPath); // 根据excel文件路径创建文件流
          response.reset();
response.setContentType("application/vnd.ms-excel;charset=UTF-8");
response.setHeader("Content-Disposition", "attachment; filename=" + java.net.URLEncoder.encode(fileName, "UTF-8"));

       ServletOutputStream ouputStream = response.getOutputStream();

       byte[] buff = new byte[1024];//设置每次写入缓存大小
        //把输出流写入客户端
        int readCount = 0;
       readCount = fis.read(buff);
       while(readCount != -1){
  ouputStream.write(buff,0,readCount);
  readCount = fis.read(buff);
}
ouputStream.flush();
ouputStream.close();
fis.close();

}catch(Exception e){
String errorMessage = "导出Excel出现异常";
ToftLogger.error(errorMessage + e.getMessage());
}finally{
      //变量置空
       fis=null;
}
    }
}