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Adds 6 new skills for Java Spring Boot development: - java-coding-standards: naming, immutability, Optional, streams - springboot-patterns: REST API, service layer, caching, async - springboot-tdd: JUnit 5, Mockito, MockMvc, Testcontainers - springboot-security: Spring Security, validation, CSRF - springboot-verification: Maven/Gradle build verification - jpa-patterns: entity design, relationships Thanks @examin!
139 lines
3.4 KiB
Markdown
139 lines
3.4 KiB
Markdown
---
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name: java-coding-standards
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description: Java coding standards for Spring Boot services: naming, immutability, Optional usage, streams, exceptions, generics, and project layout.
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---
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# Java Coding Standards
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Standards for readable, maintainable Java (17+) code in Spring Boot services.
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## Core Principles
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- Prefer clarity over cleverness
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- Immutable by default; minimize shared mutable state
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- Fail fast with meaningful exceptions
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- Consistent naming and package structure
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## Naming
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```java
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// ✅ Classes/Records: PascalCase
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public class MarketService {}
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public record Money(BigDecimal amount, Currency currency) {}
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// ✅ Methods/fields: camelCase
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private final MarketRepository marketRepository;
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public Market findBySlug(String slug) {}
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// ✅ Constants: UPPER_SNAKE_CASE
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private static final int MAX_PAGE_SIZE = 100;
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```
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## Immutability
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```java
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// ✅ Favor records and final fields
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public record MarketDto(Long id, String name, MarketStatus status) {}
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public class Market {
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private final Long id;
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private final String name;
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// getters only, no setters
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}
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```
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## Optional Usage
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```java
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// ✅ Return Optional from find* methods
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Optional<Market> market = marketRepository.findBySlug(slug);
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// ✅ Map/flatMap instead of get()
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return market
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.map(MarketResponse::from)
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.orElseThrow(() -> new EntityNotFoundException("Market not found"));
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```
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## Streams Best Practices
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```java
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// ✅ Use streams for transformations, keep pipelines short
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List<String> names = markets.stream()
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.map(Market::name)
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.filter(Objects::nonNull)
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.toList();
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// ❌ Avoid complex nested streams; prefer loops for clarity
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```
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## Exceptions
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- Use unchecked exceptions for domain errors; wrap technical exceptions with context
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- Create domain-specific exceptions (e.g., `MarketNotFoundException`)
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- Avoid broad `catch (Exception ex)` unless rethrowing/logging centrally
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```java
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throw new MarketNotFoundException(slug);
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```
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## Generics and Type Safety
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- Avoid raw types; declare generic parameters
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- Prefer bounded generics for reusable utilities
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```java
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public <T extends Identifiable> Map<Long, T> indexById(Collection<T> items) { ... }
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```
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## Project Structure (Maven/Gradle)
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```
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src/main/java/com/example/app/
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config/
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controller/
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service/
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repository/
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domain/
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dto/
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util/
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src/main/resources/
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application.yml
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src/test/java/... (mirrors main)
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```
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## Formatting and Style
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- Use 2 or 4 spaces consistently (project standard)
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- One public top-level type per file
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- Keep methods short and focused; extract helpers
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- Order members: constants, fields, constructors, public methods, protected, private
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## Code Smells to Avoid
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- Long parameter lists → use DTO/builders
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- Deep nesting → early returns
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- Magic numbers → named constants
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- Static mutable state → prefer dependency injection
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- Silent catch blocks → log and act or rethrow
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## Logging
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```java
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private static final Logger log = LoggerFactory.getLogger(MarketService.class);
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log.info("fetch_market slug={}", slug);
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log.error("failed_fetch_market slug={}", slug, ex);
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```
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## Null Handling
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- Accept `@Nullable` only when unavoidable; otherwise use `@NonNull`
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- Use Bean Validation (`@NotNull`, `@NotBlank`) on inputs
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## Testing Expectations
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- JUnit 5 + AssertJ for fluent assertions
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- Mockito for mocking; avoid partial mocks where possible
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- Favor deterministic tests; no hidden sleeps
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**Remember**: Keep code intentional, typed, and observable. Optimize for maintainability over micro-optimizations unless proven necessary.
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