Java development skill

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: choose a dependency-supported Java LTS baseline (17 or newer), infer Maven or Gradle from the surrounding repository, use JUnit 5, constructor-based design, SLF4J-compatible logging, and immutable DTOs where practical.
• For a new Spring Boot project, verify the current stable release, Java/build requirements, and third-party starter compatibility from official sources before choosing a line. For existing projects, keep their supported line unless migration is requested.
• Do not choose a persistence framework by geography or popularity. Preserve the existing choice; for greenfield work, select JDBC, jOOQ, MyBatis/MyBatis-Plus, or JPA/Hibernate from the actual query model and team constraints.
• Prefer constructor injection in DI frameworks. Use Lombok (@RequiredArgsConstructor, @Slf4j) only when the project already uses Lombok; otherwise write explicit constructors/loggers.
• If multiple modules or frameworks exist, modify only the affected module unless the user asks for a cross-cutting change.
• Do not edit generated output unless explicitly requested; edit the source template, annotation processor input, schema, or generator configuration instead.

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	add matching build-tools/..., testing/..., or code-review/... rule
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	build-tools/build-maven-dependencies.md or build-tools/build-gradle-dependencies.md
Maven pom.xml, dependencies, BOM, plugins, Java release	build-tools/build-maven-dependencies.md	relevant spring-boot/..., testing/..., or migration rule
Gradle build.gradle(.kts), wrapper, version catalog, toolchain	build-tools/build-gradle-dependencies.md	relevant spring-boot/..., testing/..., or migration rule
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-tools/... plus spring-boot/sb-rest-client.md when HTTP clients are affected
Spring Boot 3->4, Framework 7/Jakarta/Servlet baseline	spring-boot/sb-migration-3-to-4.md	build-tools/..., spring-boot/sb-rest-client.md, and affected testing/... 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	spring-boot/sb-config-profiles.md plus relevant build/framework rule
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	core/java-exception-handling.md or framework error rule
equals, hashCode, entity identity	code-review/cr-equals-hashcode.md	spring-boot/sb-jpa-repository.md or spring-boot/sb-mybatis-plus.md when entities are involved
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	testing/test-junit5.md, testing/test-mockito.md, testing/test-spring-boot-test.md, or testing/test-testcontainers.md
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	affected testing/... framework rule
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: opt-in Spring Boot 3.x + MyBatis-Plus Maven example.
• assets/pom-spring-boot-2.xml: opt-in legacy Spring Boot 2.7 maintenance example.
• assets/controller-service-test.java: opt-in Spring Boot 3 + MyBatis-Plus skeleton; split it into real files before use.
• assets/application.yml.template: opt-in multi-environment Spring Boot + MyBatis-Plus config example.