- NestJS – Custom Decorators
The two kinds worth writing. createParamDecorator for pulling the current user out of a request, and SetMetadata plus Reflector for attaching data to a route that a guard reads back — the indirection that lets one guard serve every controller instead of each one writing its own check.
- Spring Study Guide – Get Started
Start here. What this guide is, who it is for, and the exact versions every answer is written against — Spring Framework 7 and Spring Boot 4.1 on Java 21. The eight topic areas in reading order, the pizza ordering API every snippet is lifted from, and the short list of things that changed between Spring 5 and Spring 7 that will make an old answer wrong.
- Java 21 Unnamed Variables and Patterns
An unnamed variable is written _ and says "something goes here and I will not use it". It removes the invented names — ignored , unused , e2 — that clutter code where a value is structurally required but genuinely irrelevant. A note on versions This was a preview feature in Java 21, not a standard…
- Backend Dev – What a Backend Engineer Actually Does
The job, described by what lands in your queue rather than by a job posting. What you own — the API contract, the data, correctness under concurrency, and what happens at 3am — where the line sits between you and frontend, devops, DBA and data engineering, and what a real ticket looks like from request to deploy.
- Merge Sort
Split in half, sort each half, merge. O(n log n) in every case and stable, at the cost of O(n) extra space. Why stability is decided by a single <= in the merge, why the buffer should be allocated once, and why Java sorts objects this way.