java-docker
Containerize Java applications - Dockerfile optimization, JVM settings, security
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/pluginagentmarketplace/custom-plugin-java --skill java-docker- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads java-docker automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
Java Docker Skill
Containerize Java applications with optimized Dockerfiles and JVM settings.
Overview
This skill covers Docker best practices for Java including multi-stage builds, JVM container settings, security hardening, and layer optimization.
When to Use This Skill
Use when you need to:
- Create optimized Java Dockerfiles
- Configure JVM for containers
- Implement security best practices
- Reduce image size
- Set up health checks
Topics Covered
Dockerfile Optimization
- Multi-stage builds
- Layer caching strategy
- Spring Boot layered JARs
- Dependency caching
JVM Container Settings
- UseContainerSupport
- MaxRAMPercentage
- GC selection
- Exit on OOM
Security
- Non-root users
- Read-only filesystem
- Vulnerability scanning
- Secrets handling
Quick Reference
# Multi-stage optimized Dockerfile
FROM eclipse-temurin:21-jdk-alpine AS builder
WORKDIR /app
# Cache dependencies
COPY pom.xml .
COPY .mvn .mvn
RUN mvn dependency:go-offline -B
# Build and extract layers
COPY src ./src
RUN mvn package -DskipTests && \
java -Djarmode=layertools -jar target/*.jar extract
# Runtime stage
FROM eclipse-temurin:21-jre-alpine
# Security: non-root user
RUN addgroup -S app && adduser -S app -G app
USER app
WORKDIR /app
# Copy layers in order of change frequency
COPY --from=builder /app/dependencies/ ./
COPY --from=builder /app/spring-boot-loader/ ./
COPY --from=builder /app/snapshot-dependencies/ ./
COPY --from=builder /app/application/ ./
# JVM container settings
ENV JAVA_OPTS="-XX:+UseContainerSupport \
-XX:MaxRAMPercentage=75.0 \
-XX:+ExitOnOutOfMemoryError \
-XX:+UseG1GC"
EXPOSE 8080
HEALTHCHECK --interval=30s --timeout=3s --start-period=30s \
CMD wget -qO- http://localhost:8080/actuator/health/liveness || exit 1
ENTRYPOINT ["sh", "-c", "java $JAVA_OPTS org.springframework.boot.loader.launch.JarLauncher"]
JVM Container Flags
# Recommended production settings
JAVA_OPTS="
-XX:+UseContainerSupport
-XX:MaxRAMPercentage=75.0
-XX:InitialRAMPercentage=50.0
-XX:+ExitOnOutOfMemoryError
-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=/tmp/heapdump.hprof
-XX:+UseG1GC
-Djava.security.egd=file:/dev/./urandom
"
Base Image Comparison
| Image | Size | Security | Use Case |
|---|---|---|---|
| temurin:21-jre | ~200MB | Good | General use |
| temurin:21-jre-alpine | ~100MB | Good | Size-optimized |
| distroless/java21 | ~80MB | Best | Production |
Security Best Practices
# Non-root user
RUN addgroup -S app && adduser -S app -G app
USER app
# Read-only filesystem
# (Configure at runtime with --read-only)
# No shell access with distroless
FROM gcr.io/distroless/java21-debian12
# Health check
HEALTHCHECK --interval=30s --timeout=3s \
CMD wget -qO- localhost:8080/actuator/health || exit 1
Troubleshooting
Common Issues
| Problem | Cause | Solution |
|---|---|---|
| OOMKilled | Heap > limit | Set MaxRAMPercentage |
| Slow startup | Large image | Multi-stage build |
| Permission denied | Root required | Fix file permissions |
| No memory info | Old JVM | Update to Java 11+ |
Debug Checklist
□ Check container memory limits
□ Verify JVM sees container limits
□ Review health check configuration
□ Scan image for vulnerabilities
□ Test with resource constraints
Usage
Skill("java-docker")
Related Skills
java-maven-gradle- Build integrationjava-microservices- K8s deployment
FAQ
What does the java-docker skill do?
Containerize Java applications - Dockerfile optimization, JVM settings, security
How do I install java-docker?
Run npx skills add https://github.com/pluginagentmarketplace/custom-plugin-java --skill java-docker in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/java-docker/ (personal) or .claude/skills/java-docker/ (project).
Which AI agents can use java-docker?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is java-docker safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains java-docker?
It is published by pluginagentmarketplace in pluginagentmarketplace/custom-plugin-java. It has 263 recorded installs.
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