---
name: java-development
description: "Use when working on any Java or JVM project: plain Java, libraries, CLI tools, Maven/Gradle builds, Spring Boot, Jakarta EE, MyBatis/MyBatis-Plus, JPA/Hibernate, Lombok, Java tests, Java code review, API design, exception handling, security review, refactoring, dependencies, Java version upgrades, javax/jakarta migrations, or JVM runtime troubleshooting such as GC, OOM, thread dumps, deadlocks, high CPU, and performance issues."
---

# Java Development Agent

Router skill for general Java/JVM work. Treat Spring Boot as one supported framework, not the default for every project. Load only the matching rule files below.

## Defaults

- Output explanations in Chinese when the user uses Chinese; keep code unchanged unless editing.
- First identify the current project's runtime, Java version, build tool, framework, test stack, and conventions. Existing evidence beats this skill's defaults.
- Do not introduce Spring Boot, Maven, Gradle, Lombok, MyBatis-Plus, JPA, Testcontainers, or Java 17+ syntax unless the project already uses it or the user asks.
- If creating a new project and no preference is given: use Java 17+ compatibility baseline, Maven or Gradle only after asking/inferring from context, JUnit 5, constructor-based design, SLF4J-compatible logging, and immutable DTOs where practical.
- For Spring Boot projects with unknown versions, use Spring Boot 3.x / `jakarta.*` / Java 17+ as the compatibility baseline. For existing projects, keep their current supported line unless migration is requested.
- For a new China-style Spring Boot service with no persistence decision, MyBatis-Plus is acceptable; do not migrate an existing JPA/plain-MyBatis project to match that preference.
- Prefer constructor injection in DI frameworks. Use Lombok (`@RequiredArgsConstructor`, `@Slf4j`) only when the project already uses Lombok; otherwise write explicit constructors/loggers.

## Loading Rules

Start with the smallest useful set:

- Any Java task: load `core/java-general-development.md` only if project classification or default choice is unclear.
- API/exception/version work: load the specific `core/...` rule before framework rules.
- Build edits: load exactly one build rule (`build-tools/...`) matching the detected build tool.
- Spring Boot edits: load the primary `spring-boot/...` rule only when the project actually uses Spring Boot.
- Broad code review: start with `code-review/cr-anti-patterns.md`, then add specific risk files.
- Test work: load `testing/test-layering.md` first, then the framework-specific test file.
- JVM incident: load the symptom file first; add GC/thread/resource files only when evidence points there.
- Do not load README files or `examples/` unless the user asks for usage docs.

## Work Rules

- Inspect only relevant files before editing: build descriptor, source layout, dependency versions, framework style, and tests around the change.
- Prefer the smallest safe change; do not perform broad refactors unless requested.
- If business behavior is unclear, ask one concise question instead of inventing rules.
- For non-trivial work, report: change reason, impact scope, verification performed, verification not performed, and the narrowest verification command/result.

## Route By Task

| Task signal | Read first | Add if needed |
|---|---|---|
| Unknown Java project, framework-neutral edit, library/CLI code | `core/java-general-development.md` | build-tools/test/review rule in use |
| Public API, interfaces, DTOs, compatibility, library contracts | `core/java-api-design.md` | `code-review/cr-null-safety.md` |
| Exceptions, retries, interrupts, failure boundaries | `core/java-exception-handling.md` | `code-review/cr-resource-leak.md` |
| Java 8/11/17/21 upgrade, newer syntax, toolchain | `core/java-version-modernization.md` | matching build rule |
| Maven `pom.xml`, dependencies, BOM, plugins, Java release | `build-tools/build-maven-dependencies.md` | migration/test/framework rule in use |
| Gradle `build.gradle(.kts)`, wrapper, version catalog, toolchain | `build-tools/build-gradle-dependencies.md` | migration/test/framework rule in use |
| DI, beans, Lombok, service/controller skeleton | `spring-boot/sb-dependency-injection.md` | `spring-boot/sb-project-structure.md` |
| Package layout, controller/service/repository boundaries | `spring-boot/sb-project-structure.md` | `spring-boot/sb-exception-handling.md` |
| `application.yml`, profiles, secrets, config import | `spring-boot/sb-config-profiles.md` | `spring-boot/sb-actuator-health.md` |
| MyBatis, MyBatis-Plus, mapper, wrapper, pagination | `spring-boot/sb-mybatis-plus.md` | `code-review/cr-equals-hashcode.md` |
| JPA, Hibernate, N+1, lazy loading, transactions | `spring-boot/sb-jpa-repository.md` | `code-review/cr-equals-hashcode.md` |
| REST API error handling, validation errors | `spring-boot/sb-exception-handling.md` | `code-review/cr-null-safety.md` |
| HTTP clients, RestClient, WebClient, RestTemplate | `spring-boot/sb-rest-client.md` | `spring-boot/sb-config-profiles.md` |
| Actuator, health, metrics, probes | `spring-boot/sb-actuator-health.md` | `jvm/jvm-gc-logs.md` |
| Spring Boot 2->3, `javax`/`jakarta` migration | `spring-boot/sb-migration-2-to-3.md` | build + rest-client rules |
| Spring Boot 3->4, Framework 7/Jakarta/Servlet baseline | `spring-boot/sb-migration-3-to-4.md` | build + rest-client/test rules |
| Java code review, general smell scan | `code-review/cr-anti-patterns.md` | specific review files below |
| Security review, secrets, injection, crypto, deserialization, SSRF | `code-review/cr-security.md` | config/build/framework rule in use |
| Thread safety, locks, `ThreadLocal`, transactions proxy | `code-review/cr-concurrency.md` | `code-review/cr-resource-leak.md` |
| Closeable, JDBC, locks, thread pools, leaks | `code-review/cr-resource-leak.md` | `jvm/jvm-oom-analysis.md` |
| NPE, `Optional`, nullable contracts | `code-review/cr-null-safety.md` | framework error rule in use |
| `equals`, `hashCode`, entity identity | `code-review/cr-equals-hashcode.md` | persistence rule in use |
| Stream API, parallel stream, lambda side effects | `code-review/cr-stream-pitfalls.md` | `code-review/cr-concurrency.md` |
| Test strategy, unit/slice/integration choice | `testing/test-layering.md` | one test framework file |
| JUnit 5 lifecycle, parameterized tests | `testing/test-junit5.md` | `testing/test-coverage-assertj.md` |
| Mockito mocks, spies, static mocks | `testing/test-mockito.md` | `testing/test-layering.md` |
| Testcontainers, real DB/Redis/Kafka | `testing/test-testcontainers.md` | `testing/test-spring-boot-test.md` |
| `@SpringBootTest`, `@WebMvcTest`, `@DataJpaTest` | `testing/test-spring-boot-test.md` | `testing/test-testcontainers.md` |
| AssertJ, JaCoCo, coverage floor | `testing/test-coverage-assertj.md` | framework-specific test file |
| OOM, heap dump, memory leak | `jvm/jvm-oom-analysis.md` | `code-review/cr-resource-leak.md` |
| High CPU, hot thread, profiling | `jvm/jvm-cpu-high.md` | `jvm/jvm-thread-dump.md` |
| Hang, deadlock, thread leak | `jvm/jvm-thread-dump.md` | `code-review/cr-concurrency.md` |
| GC pause, heap sizing, collector choice | `jvm/jvm-gc-tuning.md` | `jvm/jvm-gc-logs.md` |
| GC log interpretation | `jvm/jvm-gc-logs.md` | `jvm/jvm-gc-tuning.md` |

## Assets

- `assets/pom-spring-boot-3.xml`: Spring Boot 3.x Maven baseline.
- `assets/pom-spring-boot-2.xml`: Spring Boot 2.x Maven baseline.
- `assets/controller-service-test.java`: Controller + service + test skeleton.
- `assets/application.yml.template`: multi-environment config template.