Java REST API Design Principles
Apply REST API design principles for Spring Boot applications.
What is covered in this Skill?
- HTTP methods (GET, POST, PUT, PATCH, DELETE) — semantic consistency
- Resource URI design
- HTTP status codes
- Request/response DTOs with lean contracts
- API versioning (URI, header, or media type — applied consistently)
- Bean Validation at the boundary (@Valid/@Validated on controller inputs, 400 on failure)
- Pagination, sorting, and filtering (Page/Pageable with caps)
- ISO-8601 instants with offset (OffsetDateTime, Instant) in JSON contracts
- Content negotiation (JSON default; vendor media types when meaningful)
- Idempotency-Key support for POST creates; 409 Conflict for collisions
- ETag concurrency with If-Match/If-None-Match; 412 Precondition Failed / 304 Not Modified
- HTTP caching discipline (Cache-Control, ETag, Last-Modified)
- Deprecation and sunset headers (Deprecation, Sunset, Link rel="successor-version)"
- Error handling
- API security (TLS, authentication, authorization, input validation)
- API contract: OpenAPI file as source of truth for API-first (OpenAPI Generator)
- Controller advice and problem details (RFC 7807)
Scope: Apply recommendations based on the reference rules and good/bad code examples.
Constraints
Before applying any REST API changes, ensure the project compiles. If compilation fails, stop immediately. After applying improvements, run full verification.
- MANDATORY: Run
./mvnw compile or mvn compile before applying any change
- SAFETY: If compilation fails, stop immediately
- VERIFY: Run
./mvnw clean verify or mvn clean verify after applying improvements
- BEFORE APPLYING: Read the reference for detailed rules and good/bad patterns
- EDGE CASE: If request scope is ambiguous, stop and ask a clarifying question before applying changes
- EDGE CASE: If required inputs, files, or tooling are missing, report what is missing and ask whether to proceed with setup guidance
When to use this skill
- Review Java code for Spring Boot REST API
- Apply best practices for Spring Boot REST API in Java code
- Design Spring Boot REST controllers and DTOs
- Add Problem Details error responses in Spring Boot REST
- Improve pagination validation or idempotency in Spring APIs
Workflow
- Read reference and assess project context
Read references/302-frameworks-spring-boot-rest.md and inspect the current project setup before proposing changes.
- Gather scope and decide target improvements
Identify requested outcomes, constraints, and the minimum safe set of changes to apply.
- Apply framework-aligned changes
Implement or refactor configuration/code following the reference patterns and project conventions.
- Run verification and report results
Execute appropriate build/tests and summarize what changed, what was verified, and any follow-up actions.
Reference
For detailed guidance, examples, and constraints, see references/302-frameworks-spring-boot-rest.md.