Develop and maintain plain Java projects using their existing JDK version and build conventions. Covers Maven and Gradle, dependency management, logging, error handling, code checks, packaging, and build verification without silently introducing upgrades or tools.
Day-to-day plain Java development without a framework: Maven and Gradle usage and wrappers, project layout, dependency and vulnerability management, modern Java idioms by JDK version (records, sealed types, pattern matching, virtual threads), SLF4J logging, error and null handling, immutability, concurrency basics, static analysis and formatting (Spotless, Error Prone, -Xlint), packaging (jar, jlink, jpackage) and GitHub Actions CI. Use when writing, building, reviewing or maintaining ordinary Java code.
Run score Not tested
See how to installThis skill supports Java implementation, builds, reviews, and maintenance without assuming a particular framework. It checks the project’s existing settings and source conventions, then works within its Maven or Gradle setup. Topics include dependency organization, logging, exceptions and null handling, basic concurrency, and choosing language features supported by the project’s JDK. It can also use configured code checks and formatting tools, and help create deliverables such as JAR files.
Use it when changing an existing project while following its established conventions, investigating dependency conflicts, or diagnosing a failed build. It can also help determine whether features such as records or virtual threads fit the project’s Java version. Changes are verified through the project’s build process.
The project needs a suitable JDK and Maven or Gradle; use its wrapper when available. Confirm before Java or dependency upgrades, public API changes, adding runtime libraries or build tools, or changing CI. Preview features are used only when explicitly selected.
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Not counted in the score. Rated by AI (OpenAI Codex) as of Oct 25, 2026. Treat it as a guide and read the original before installing.
Review the instructions the agent will receive before you install.
Everyday guidance for Java projects that are not tied to a framework. If the project uses Spring Boot, Quarkus, Helidon or similar, prefer that framework's skills for framework concerns and use this one for the plain-Java parts.
pom.xml/build.gradle*, .mvn/, gradle/, .java-version/.sdkmanrc, .editorconfig, CI files, and a few source files. Match the build tool, Java release, formatter, naming, logging and test libraries already in use.java-upgrade, if installed)../mvnw, ./gradlew) when present; otherwise the installed mvn/gradle. Do not commit a wrapper unprompted../mvnw -B verify or ./gradlew build) and report the result. Run a narrower command first while iterating. If you could not run it, say so.Check maven.compiler.release/<release>, java.toolchain, or sourceCompatibility; never use a feature newer than that release. Summary (details and snippets in references/modern-java.md):
| Release | You can use |
|---|---|
| 8 | lambdas, streams, Optional, java.time |
| 11 | var, String.isBlank/strip/lines, java.net.http.HttpClient, List.of/Map.of (9) |
| 17 | records, sealed classes, text blocks, switch expressions, instanceof patterns |
| 21 | pattern matching for switch, record patterns, virtual threads, SequencedCollection (getFirst/getLast/reversed) |
| 22-24 | unnamed variables _ (22), Stream.gather (24) |
| 25 | scoped values, instance main/compact source files, module import declarations (all final) |
Structured concurrency (StructuredTaskScope) is still a preview API in 25 and 27 (verified: needs --enable-preview); do not use it in production code unless the user opts in to preview features.
./mvnw -B verify (compile, unit tests, integration tests, packaging), -pl <module> -am for one module, dependency:tree, -DskipTests only when the user asks. Gradle: ./gradlew build, test --tests 'pkg.Class', dependencies, dependencyInsight --dependency <name>.src/main/java, src/main/resources, src/test/java, src/test/resources; package by feature, one top-level type per file, no split packages.maven.compiler.release / Gradle toolchain with options.release) and UTF-8 encoding; do not rely on the JDK that happens to run the build.dependency:tree/versions: usage, version catalogs and multi-module layout: references/build-and-dependencies.md.junit-bom, testcontainers-bom, the framework's BOM) instead of repeating versions; one version per library across modules.mvn dependency:tree -Dincludes=group:artifact / gradlew dependencyInsight. Resolve conflicts with dependencyManagement or Gradle constraints, not by excluding randomly.mvn versions:display-dependency-updates (add -Dmaven.version.ignore to hide alpha/beta/RC) and report them; do not apply major upgrades without asking.-proc:none is the default unless -processor, --processor-path or --processor-module-path is given. Declare the processor path in the build (Maven annotationProcessorPaths, Gradle annotationProcessor) or pass -proc:full. JDK 21+ prints a warning when it detects implicit use; -proc:full is also backported to 17.0.11, 11.0.23 and 8u411. Source: https://inside.java/2024/06/18/quality-heads-up/.synchronized: on JDK 21-23 a virtual thread that blocks inside synchronized is pinned to its carrier; JEP 491 removes nearly all such pinning in JDK 24+. On 21-23 prefer ReentrantLock around blocking calls. Source: https://openjdk.org/jeps/491.--add-exports/--add-opens javac flags, and on JDK 21 -XDaddTypeAnnotationsToSymbol=true (see the quality reference).Respect what is configured: if the project uses Spotless/Checkstyle/SpotBugs/Error Prone, run them and fix findings; if not, do not add them. When asked to introduce them, start with -Xlint:all and Spotless (formatter only), then Error Prone. Verified configs for Maven and Gradle on JDK 21 and 25 (including the JDK-21-only -XDaddTypeAnnotationsToSymbol=true requirement and Maven .mvn/jvm.config flags) are in references/quality-and-packaging.md. Never reformat the whole codebase in an unrelated change.
mvn package/gradlew jar. Runnable app: shaded/fat jar or lib/ directory plus manifest Main-Class; custom runtime with jlink; native installer/app-image with jpackage (verified on macOS, see references/quality-and-packaging.md).actions/checkout, actions/setup-java with distribution: temurin, an explicit java-version, built-in dependency cache, then ./mvnw -B verify or ./gradlew build. Snippet and notes in references/quality-and-packaging.md. Do not change CI without asking.java-junit (unit tests), java-testcontainers (integration tests with Docker), java-hibernate-jpa (persistence), java-debugging (failures and stack traces), java-diagnostics (performance, memory, threads, JFR), java-upgrade (JDK/framework upgrades), lsp-setup (Java language server for navigation and refactoring).
references/modern-java.md: idioms and verified snippets (records, sealed types, switch patterns, text blocks, virtual threads, SequencedCollection, unnamed variables), preview status, pitfalls.references/build-and-dependencies.md: Maven/Gradle commands, wrappers, BOMs, conflict diagnosis, update checking, Dependabot/Renovate, vulnerability scanning.references/quality-and-packaging.md: logging setup, -Xlint, Spotless, Error Prone, Checkstyle/SpotBugs notes, jar/jlink/jpackage, GitHub Actions.No reviews yet. Tell others what you thought.
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