public static org.apereo.cas.web.UrlValidator getInstance() {
        if (INSTANCE == null) {
            INSTANCE = new SimpleUrlValidator(UrlValidator.getInstance(), DomainValidator.getInstance());
        }
        return INSTANCE;
    }
Gets a static instance to be used internal only.

@return the instance
core/cas-server-core-web-api/src/main/java/org/apereo/cas/web/SimpleUrlValidator.java