The reason for this error is that the value placed when using the conversion is a set (list), and the object is indeed obtained.
String str = (String) redisTemplate.opsForValue().get("categoriesList");
jsonBean.setData(FastJsonUtils.convertJsonToObject(str,Category.class));
Solution: After obtaining str, it is converted into a collection
List<Category> categoryList = FastJsonUtils.toList(str, Category.class);
jsonBean.setData(categoryList);