Ai-agent-instructions java-coding

Expert Java development covering Spring Boot applications, REST APIs, service layer patterns, dependency injection, error handling, and production-ready code. Applies clean architecture, proper exception handling, logging, and performance best practices. Use this skill when writing Java code, creating Spring Boot services, designing REST APIs, implementing business logic, or working with any .java files — including controllers, services, repositories, DTOs, and configuration classes.

install

source · Clone the upstream repo

git clone https://github.com/khumbal/ai-agent-instructions

Claude Code · Install into ~/.claude/skills/

T=$(mktemp -d) && git clone --depth=1 https://github.com/khumbal/ai-agent-instructions "$T" && mkdir -p ~/.claude/skills && cp -r "$T/.copilot/skills/java-coding" ~/.claude/skills/khumbal-ai-agent-instructions-java-coding && rm -rf "$T"

manifest: .copilot/skills/java-coding/SKILL.md

source content

Java Coding

When to use this skill

Use when writing or modifying Java code, creating Spring Boot services, designing REST APIs, implementing business logic, or working with any .java files.

Conditional workflow

Determine what you're building:

New REST endpoint? → Controller (thin) → Service (logic) → Repository (data) Business logic? → Service layer with
```
@Transactional
```
, proper error handling New entity/DTO? → Records for DTOs, entities separate from API surface Bug fix? → Read existing code first, understand the flow, fix with tests

Architecture rules

Follow strict layered architecture:

Request → Controller → Service → Repository → Database
            ↓              ↓
         Validate      Business logic
         Map DTO       Transactions
         HTTP status   Error handling

Controller: Thin — validate input, map DTOs, return HTTP status. No business logic.
Service: Business rules,
```
@Transactional
```
boundaries, orchestrate repository calls.
Repository: Data access only. Spring Data JPA methods.

Code patterns

See Spring Boot patterns for complete Controller, Service, Exception Handler, and Business Exception templates.

Mandatory conventions

Practice	Do	Don't
DTOs	Separate request/response DTOs (Records)	Expose JPA entities in API
Transactions	`@Transactional` on service methods	`@Transactional` on controllers
Validation	`@Valid` on controller params	Manual null checks everywhere
Logging	SLF4J `@Slf4j` , structured context	`System.out.println`
Nulls	`Optional` returns, `@NonNull`	Return null from services
Dependencies	Constructor injection ( `@RequiredArgsConstructor` )	Field injection ( `@Autowired` )

Performance rules

```
@Transactional(readOnly = true)
```
for read operations
Avoid N+1: use
```
@EntityGraph
```
or JOIN FETCH
Pagination for list endpoints (
```
Pageable
```
)
```
@Cacheable
```
for frequently accessed, rarely changed data
Profile before optimizing — don't guess

Feedback loop

After writing/modifying code:

Run
```
mvn compile
```
→ fix compile errors
Run relevant tests → fix failures
Check for missing error handling or edge cases
If any step fails → fix → restart from step 1