@SuppressWarnings("unchecked")
    private void createExtension(final String name, final Holder<Object> holder) {
        ClassEntity classEntity = getExtensionClassesEntity().get(name);
        if (Objects.isNull(classEntity)) {
            throw new IllegalArgumentException(name + " name is error");
        }
        Class<?> aClass = classEntity.getClazz();
        Object o = joinInstances.get(aClass);
        if (Objects.isNull(o)) {
            o = createExtension(classEntity);
            if (classEntity.isSingleton()) {
                joinInstances.putIfAbsent(aClass, o);
                o = joinInstances.get(aClass);
            }
        }
        holder.setOrder(classEntity.getOrder());
        holder.setValue(o);
    }
get all join spi.

@return list. joins
shenyu-spi/src/main/java/org/apache/shenyu/spi/ExtensionLoader.java