302 Frameworks Spring Boot REST Agent Skill

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.