public static String appendScheme(final String url, final String scheme) {
        String schemeUrl = url;
        if (!schemeUrl.startsWith("http://") && !schemeUrl.startsWith("https://")) {
            schemeUrl = scheme + "://" + schemeUrl;
        }
        return schemeUrl;
    }
appendScheme.

@param scheme scheme
@param url    url
@return {@link String}
shenyu-common/src/main/java/org/apache/shenyu/common/utils/UriUtils.java