后台java (jdk>=1.8)：

byte[] bytes = byteArrayOutputStream.toByteArray();

String base64Str = java.util.Base64.getEncoder().encodeToString(bytes);

前端：

function dataURLtoBlob(base64Str) {

var bstr = atob(base64Str), n = bstr.length, u8arr = new Uint8Array(n);

while (n--) {

u8arr[n] = bstr.charCodeAt(n);

}

return new Blob([u8arr], { type: "application/vnd.ms-excel" }); //该类型为xls

}

var blob = dataURLtoBlob(base64Str);

var downloadUrl = window.URL.createObjectURL(blob);

var anchor = document.createElement("a");

anchor.href = downloadUrl;

anchor.download = "aa.xls";

anchor.click();

window.URL.revokeObjectURL(blob);

其他类型：

‘doc‘ => ‘application/msword‘,

‘bin‘ => ‘application/octet-stream‘,

‘exe‘ => ‘application/octet-stream‘,

‘so‘ => ‘application/octet-stream‘,

‘dll‘ => ‘application/octet-stream‘,

‘pdf‘ => ‘application/pdf‘,

‘ai‘ => ‘application/postscript‘,

‘xls‘ => ‘application/vnd.ms-excel‘,

‘ppt‘ => ‘application/vnd.ms-powerpoint‘,

‘dir‘ => ‘application/x-director‘,

‘js‘ => ‘application/x-javascript‘,

‘swf‘ => ‘application/x-shockwave-flash‘,

‘xhtml‘ => ‘application/xhtml+xml‘,

‘xht‘ => ‘application/xhtml+xml‘,

‘zip‘ => ‘application/zip‘,

‘mid‘ => ‘audio/midi‘,

‘midi‘ => ‘audio/midi‘,

‘mp3‘ => ‘audio/mpeg‘,

‘rm‘ => ‘audio/x-pn-realaudio‘,

‘rpm‘ => ‘audio/x-pn-realaudio-plugin‘,

‘wav‘ => ‘audio/x-wav‘,

‘bmp‘ => ‘image/bmp‘,

‘gif‘ => ‘image/gif‘,

‘jpeg‘ => ‘image/jpeg‘,

‘jpg‘ => ‘image/jpeg‘,

‘png‘ => ‘image/png‘,

‘css‘ => ‘text/css‘,

‘html‘ => ‘text/html‘,

‘htm‘ => ‘text/html‘,

‘txt‘ => ‘text/plain‘,

‘xsl‘ => ‘text/xml‘,

‘xml‘ => ‘text/xml‘,

‘mpeg‘ => ‘video/mpeg‘,

‘mpg‘ => ‘video/mpeg‘,

‘avi‘ => ‘video/x-msvideo‘,

‘movie‘ => ‘video/x-sgi-movie‘,

原文：https://www.cnblogs.com/shihx/p/12578636.html