# Java Patterns

> This skill should be used for Java/Spring patterns, dependency injection, streams, Optional, Kotlin, Spring Boot, Maven, Gradle, JVM backend

- Skill: `majiayu000/java-patterns` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add majiayu000/java-patterns`
- Raw SKILL.md: https://api.skillmd.com/api/skills/majiayu000/java-patterns/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: majiayu000 (https://skillmd.com/u/majiayu000)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/majiayu000/java-patterns

---


# Java Patterns

Idiomatic Java/Spring patterns for Java 17+.

## Records

```java
public record User(String name, String email) {}
```

## Optional

```java
Optional.ofNullable(user)
    .map(User::getEmail)
    .orElse("default@example.com");
```

## Streams

```java
List<String> names = users.stream()
    .filter(u -> u.isActive())
    .map(User::getName)
    .collect(Collectors.toList());
```

## Spring Dependency Injection

```java
@Service
public class UserService {
    private final UserRepository repo;

    public UserService(UserRepository repo) {
        this.repo = repo;
    }
}
```

## JUnit 5

```java
@Test
void shouldReturnUser() {
    User user = service.findById(1L);
    assertThat(user.getName()).isEqualTo("test");
}

@ParameterizedTest
@ValueSource(strings = {"a", "b", "c"})
void shouldValidate(String input) {
    assertTrue(validator.isValid(input));
}
```