获取浏览器信息

通过获取请求头中字段user-agent来判别

if (isIE) { 
    displayFilename = URLEncoder.encode(displayFilename, "UTF-8"); 
    response.setHeader("Content-Disposition", "attachment;filename=\"" + displayFilename + "\""); 
} else { 
    displayFilename = new String(displayFilename.getBytes("UTF-8"), "ISO8859-1"); 
     response.setHeader("Content-Disposition", "attachment;filename=" + displayFilename);
}
// 对文件下载乱码问题时候有效，需要验证