# Java Coding Standards

> Java coding standards for Spring Boot services: naming, immutability, Optional usage, streams, exceptions, generics, and project layout.

- **Type:** Skill
- **Install:** `agentstack add skill-helloggx-skill-java-coding-standards`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [HelloGGX](https://agentstack.voostack.com/s/helloggx)
- **Installs:** 0
- **Category:** [Agent Skills](https://agentstack.voostack.com/c/agent-skills)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [HelloGGX](https://github.com/HelloGGX)
- **Source:** https://github.com/HelloGGX/skill/tree/main/skill/java-coding-standards

## Install

```sh
agentstack add skill-helloggx-skill-java-coding-standards
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# Java Coding Standards

Standards for readable, maintainable Java (17+) code in Spring Boot services.

## When to Activate

- Writing or reviewing Java code in Spring Boot projects
- Enforcing naming, immutability, or exception handling conventions
- Working with records, sealed classes, or pattern matching (Java 17+)
- Reviewing use of Optional, streams, or generics
- Structuring packages and project layout

## Core Principles

- Prefer clarity over cleverness
- Immutable by default; minimize shared mutable state
- Fail fast with meaningful exceptions
- Consistent naming and package structure

## Naming

```java
// ✅ Classes/Records: PascalCase
public class MarketService {}
public record Money(BigDecimal amount, Currency currency) {}

// ✅ Methods/fields: camelCase
private final MarketRepository marketRepository;
public Market findBySlug(String slug) {}

// ✅ Constants: UPPER_SNAKE_CASE
private static final int MAX_PAGE_SIZE = 100;
```

## Immutability

```java
// ✅ Favor records and final fields
public record MarketDto(Long id, String name, MarketStatus status) {}

public class Market {
  private final Long id;
  private final String name;
  // getters only, no setters
}
```

## Optional Usage

```java
// ✅ Return Optional from find* methods
Optional market = marketRepository.findBySlug(slug);

// ✅ Map/flatMap instead of get()
return market
    .map(MarketResponse::from)
    .orElseThrow(() -> new EntityNotFoundException("Market not found"));
```

## Streams Best Practices

```java
// ✅ Use streams for transformations, keep pipelines short
List names = markets.stream()
    .map(Market::name)
    .filter(Objects::nonNull)
    .toList();

// ❌ Avoid complex nested streams; prefer loops for clarity
```

## Exceptions

- Use unchecked exceptions for domain errors; wrap technical exceptions with context
- Create domain-specific exceptions (e.g., `MarketNotFoundException`)
- Avoid broad `catch (Exception ex)` unless rethrowing/logging centrally

```java
throw new MarketNotFoundException(slug);
```

## Generics and Type Safety

- Avoid raw types; declare generic parameters
- Prefer bounded generics for reusable utilities

```java
public  Map indexById(Collection items) { ... }
```

## Project Structure (Maven/Gradle)

```
src/main/java/com/example/app/
  config/
  controller/
  service/
  repository/
  domain/
  dto/
  util/
src/main/resources/
  application.yml
src/test/java/... (mirrors main)
```

## Formatting and Style

- Use 2 or 4 spaces consistently (project standard)
- One public top-level type per file
- Keep methods short and focused; extract helpers
- Order members: constants, fields, constructors, public methods, protected, private

## Code Smells to Avoid

- Long parameter lists → use DTO/builders
- Deep nesting → early returns
- Magic numbers → named constants
- Static mutable state → prefer dependency injection
- Silent catch blocks → log and act or rethrow

## Logging

```java
private static final Logger log = LoggerFactory.getLogger(MarketService.class);
log.info("fetch_market slug={}", slug);
log.error("failed_fetch_market slug={}", slug, ex);
```

## Null Handling

- Accept `@Nullable` only when unavoidable; otherwise use `@NonNull`
- Use Bean Validation (`@NotNull`, `@NotBlank`) on inputs

## Testing Expectations

- JUnit 5 + AssertJ for fluent assertions
- Mockito for mocking; avoid partial mocks where possible
- Favor deterministic tests; no hidden sleeps

**Remember**: Keep code intentional, typed, and observable. Optimize for maintainability over micro-optimizations unless proven necessary.

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [HelloGGX](https://github.com/HelloGGX)
- **Source:** [HelloGGX/skill](https://github.com/HelloGGX/skill)
- **License:** MIT

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-helloggx-skill-java-coding-standards
- Seller: https://agentstack.voostack.com/s/helloggx
- Browse the marketplace: https://agentstack.voostack.com/browse

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Listed on AgentStack — the marketplace for AI agent skills and MCP servers. Every listing is security-reviewed. Creators keep 70%.