src/main/java/io/github/biezhi/wechat/utils/WeChatUtils.java
public static String getMimeType(String fileUrl) {
        FileNameMap fileNameMap = URLConnection.getFileNameMap();
        String      type        = fileNameMap.getContentTypeFor(fileUrl);
        return type;
    }
public static String getMimeType(String fileUrl) {
        FileNameMap fileNameMap = URLConnection.getFileNameMap();
        String      type        = fileNameMap.getContentTypeFor(fileUrl);
        return type;
    }
获取文件 MimeType

@param fileUrl
@return