base64解码并生成文件

BASE64Decoder decoder = new BASE64Decoder();
byte[] b = decoder.decodeBuffer(base64);//base64为base64编码的字符串
FileOutputStream fos = null;

for (int i = 0; i < b.length; i++){
    if (b[i] < 0) {
        b[i] += 256;
    }
}

fos = new FileOutputStream("xxx");
fos.write(b);
fos.flush();
fos.close();