去年的OSS还是链接可预览，今年可能是阿里云OSS升级了，变成直接下载了。
所以重新改回预览，其他全部不变，上传添加 contentType 配置

//文件名
String originalFilename = file.getOriginalFilename();
//拿到.后缀
String type = originalFilename.substring(originalFilename.lastIndexOf("."));

ObjectMetadata metadata = new ObjectMetadata();
metadata.setContentType(getcontentType(type));

getcontentType 为判断文件类型：

public static String getcontentType(String filenameExtension) {
    if (".pdf".equalsIgnoreCase(filenameExtension)) {
        return "application/pdf";
    }
    if (".bmp".equalsIgnoreCase(filenameExtension)) {
        return "image/bmp";
    }
    if (".gif".equalsIgnoreCase(filenameExtension)) {
        return "image/gif";
    }
    if (".jpeg".equalsIgnoreCase(filenameExtension) ||
            ".jpg".equalsIgnoreCase(filenameExtension) ||
            ".png".equalsIgnoreCase(filenameExtension)) {
        return "image/jpg";
    }
    if (".html".equalsIgnoreCase(filenameExtension)) {
        return "text/html";
    }
    if (".txt".equalsIgnoreCase(filenameExtension)) {
        return "text/plain";
    }
    if (".vsd".equalsIgnoreCase(filenameExtension)) {
        return "application/vnd.visio";
    }
    if (".pptx".equalsIgnoreCase(filenameExtension) ||
            ".ppt".equalsIgnoreCase(filenameExtension)) {
        return "application/vnd.ms-powerpoint";
    }
    if (".docx".equalsIgnoreCase(filenameExtension)) {
        return "application/msword";
    }
    if (".xml".equalsIgnoreCase(filenameExtension)) {
        return "text/xml";
    }
    return "image/jpg";
}