presets.dev: Instructions file for GitHub Copilot

Spring Boot Copilot Instructions: Injection, Transactions and Validation

Path-specific Copilot instructions for Spring Boot. They apply through applyTo and leave .github/copilot-instructions.md in place.

Updated for Spring Boot 4.1, Nov 2026

Do not upgrade dependencies or the framework version unless the task asks.

Stay on the Spring Boot and JDK the build already uses. For a new service, Boot 4.1 is the stable line to write for. Do not add an M, RC, or SNAPSHOT version because a blog shows it. A lazy DataSource connection is an option you turn on for a reason, not a default you copy into every app. Read pom.xml or build.gradle before you add a starter.

Project shape

A web app splits controller, application service, and persistence. The controller maps HTTP. The service owns the use case and the transaction. The repository talks to the database. Do not put business rules in the controller.

Constructor injection is the default. Do not use field injection. A new bean is a constructor argument, not a static lookup.

Validation and HTTP

Validate input with the project's Bean Validation annotations on the request DTO. A controller checks the binding result the way neighbors do. Do not trust a path id as proof the caller owns the row. Load the row and authorize.

Return the status the API already uses. A not-found and a forbidden are different. Do not catch every exception and return 200.

Transactions and data

@Transactional sits on the service method that must commit or roll back together. Spring applies it with a proxy. A call from another method in the same class, this.save(), does not pass through that proxy, so @Transactional and @Async on the callee do not run. The same is true for a private method. Call through an injected bean, or move the boundary to the method that is actually invoked from outside. Do not call a remote HTTP API inside the transaction. Keep the transaction short.

A JPA query fetches what it needs. An open session that lazy-loads a collection in a loop is an N+1. Use a fetch join or a projection the project already prefers. Pagination has a page size cap.