public boolean containsReference(Object value) {
        if (references == null) {
            return false;
        }

        SerialContext refContext = references.get(value);
        if (refContext == null) {
            return false;
        }

        if (value == Collections.emptyMap()) {
            return false;
        }

        Object fieldName = refContext.fieldName;

        return fieldName == null || fieldName instanceof Integer || fieldName instanceof String;
    }
Set global date format pattern in FastJsonConfig

@param dateFormatPattern global date format pattern
src/main/java/com/alibaba/fastjson/serializer/JSONSerializer.java