为什么浏览器对有些图片是直接预览打开，对有些图片是直接下载？—— 原由就在Content-Type响应头上；

Content-Type响应头的作用：

Content-Type 用于向接收方说明传输资源的媒体类型，从而让浏览器用指定码表去解码。

以下举例说明MinIO上传时如何设置Content-Type

MinIO

上传时参数设置的代码片段

// 上传参数中指定
PutObjectArgs putObjectArgs = PutObjectArgs.builder()
                    .bucket(bucket)
                    .object(objectName)
            // 上传时指定对应对ContentType
                    .contentType(ViewContentType.getContentType(objectName))
                    .stream(multipartFile.getInputStream(), multipartFile.getSize(), 1024*1024*5+1)
                    .build();

列举部分图片的Content-Type

public enum ViewContentType {
    DEFAULT("default","application/octet-stream"),
    JPG("jpg", "image/jpeg"),
    TIFF("tiff", "image/tiff"),
    GIF("gif", "image/gif"),
    JFIF("jfif", "image/jpeg"),
    PNG("png", "image/png"),
    TIF("tif", "image/tiff"),
    ICO("ico", "image/x-icon"),
    JPEG("jpeg", "image/jpeg"),
    WBMP("wbmp", "image/vnd.wap.wbmp"),
    FAX("fax", "image/fax"),
    NET("net", "image/pnetvue"),
    JPE("jpe", "image/jpeg"),
    RP("rp", "image/vnd.rn-realpix");

    private String prefix;

    private String type;

    public static String getContentType(String prefix){
        if(StrUtil.isEmpty(prefix)){
            return DEFAULT.getType();
        }
        prefix = prefix.substring(prefix.lastIndexOf(".") + 1);
        for (ViewContentType value : ViewContentType.values()) {
            if(prefix.equalsIgnoreCase(value.getPrefix())){
                return value.getType();
            }
        }
        return DEFAULT.getType();
    }

    ViewContentType(String prefix, String type) {
        this.prefix = prefix;
        this.type = type;
    }

    public String getPrefix() {
        return prefix;
    }

    public String getType() {
        return type;
    }
}