core/src/main/java/org/nanohttpd/protocols/http/NanoHTTPD.java
public static String getMimeTypeForFile(String uri) {
        int dot = uri.lastIndexOf('.');
        String mime = null;
        if (dot >= 0) {
            mime = mimeTypes().get(uri.substring(dot + 1).toLowerCase());
        }
        return mime == null ? "application/octet-stream" : mime;
    }
public static String getMimeTypeForFile(String uri) {
        int dot = uri.lastIndexOf('.');
        String mime = null;
        if (dot >= 0) {
            mime = mimeTypes().get(uri.substring(dot + 1).toLowerCase());
        }
        return mime == null ? "application/octet-stream" : mime;
    }
Get MIME type from file name extension, if possible

@param uri
the string representing a file
@return the connected mime/type