MultipartFile（file）转为Base64

首先将   MultipartFile   文件转为byte[]数组形式，可以参考以下方法

private byte[] convertToByteArray(MultipartFile file) throws IOException {
        InputStream inputStream = null;
        try {
            inputStream = file.getInputStream();
            byte[] bytes = new byte[inputStream.available()];
            inputStream.read(bytes);
            return bytes;
        } finally {
            if (inputStream != null) {
                inputStream.close();
            }
        }
    }

然后使用java.util自带的Base64工具即可转换

@Override
    public String updateUserAvatar(MultipartFile file) {
        //将file文件转为Base64
        byte[] bytes = new byte[0];
        try {
            bytes = this.convertToByteArray(file);
        } catch (IOException e) {
            return "";
        }
        String avatar = Base64.getEncoder().encodeToString(bytes);

        return avatar;
    }