private Map<String, ClassEntity> getExtensionClassesEntity() {
        Map<String, ClassEntity> classes = cachedClasses.getValue();
        if (Objects.isNull(classes)) {
            synchronized (cachedClasses) {
                classes = cachedClasses.getValue();
                if (Objects.isNull(classes)) {
                    classes = loadExtensionClass();
                    cachedClasses.setValue(classes);
                    cachedClasses.setOrder(0);
                }
            }
        }
        return classes;
    }
Gets extension classes.

@return the extension classes
shenyu-spi/src/main/java/org/apache/shenyu/spi/ExtensionLoader.java