Java Optional chain used properly in Spring Boot LLM app

The category of an expense was decided entirely by the model. When it got one wrong, you could fix it in the app — and the next purchase from the same shop would arrive wrong again, because nothing remembered the fix. So the order gets inverted. What the same merchant was categorised as before comes first, and the model's answer becomes the fallback behind it. That is one expression: a lookup that may find nothing, or the parsed category, or NOT_RECOGNIZED when neither answers. Along the way: why a query that returns Optional needs flatMap and not map, why or() takes a supplier, and why "Other" is the wrong name for a value that means nobody knows. Also two full reversals — I move the category into a record and then move it back to a plain string, and both are left in. This is real code from an expense tracker I build in public, on Java 25 and Spring Boot. Nothing is a textbook example. 00:00 The category the model got wrong 00:34 Making the model a fallback instead of the source 01:25 A class to resolve the category 02:15 String, or a record? 03:23 Other becomes NOT_RECOGNIZED 04:22 Where a category can come from 05:20 Reading the account's own history 05:57 A derived query by account and merchant 06:41 The latest one, ordered by created date 07:18 The merchant can be null 08:49 Optional inside Optional, and flatMap 10:32 orElse and the not-recognized fallback 11:13 Falling back to the model 12:35 orElseGet and the supplier 13:03 Fix it once instead of every time 13:37 Back to a plain string 14:58 Wrap-up Source code: https://github.com/Bogr11/cash-lens-y... Full series:    • Building in Public: AI Expense Tracker wit...   #Java #Optional #SpringBoot