Detection
migetpacks detects a Java application when any of the following files are present in the project root:
pom.xml (Maven)build.gradle (Gradle, Groovy DSL)build.gradle.kts (Gradle, Kotlin DSL)
Version Detection
Java version is resolved in the following priority order:
| Source | Example |
|---|
.java-version | 21 |
system.properties | java.runtime.version=21 |
pom.xml (<java.version> or <maven.compiler.release>) | <java.version>21</java.version> |
| Default | 21 |
Version Normalization
Legacy version formats are normalized for Docker image compatibility:
| Input | Normalized |
|---|
1.8 | 8 |
1.11 | 11 |
17 | 17 |
21 | 21 |
Build Process
migetpacks automatically detects the build tool:
| File Present | Build Tool | Build Image |
|---|
pom.xml | Maven | maven:3-eclipse-temurin-{version} |
build.gradle or build.gradle.kts | Gradle | gradle:jdk{version} |
Gradle Wrapper
If gradlew is present in the project root, migetpacks uses the Gradle Wrapper instead of the system Gradle for correct version compatibility.
Generated Dockerfile
# Build stage
FROM maven:3-eclipse-temurin-21 AS builder
WORKDIR /build
# Layer caching: copy build files first
COPY pom.xml ./
# Download dependencies (cached if pom.xml unchanged)
RUN mvn dependency:go-offline -B || true
# Copy source code
COPY . .
# Build and cleanup source
RUN mvn package -DskipTests -B \
&& rm -rf src/ .mvn/ mvnw* pom.xml
# Runtime stage
FROM eclipse-temurin:21-jre
WORKDIR /app
COPY --from=builder --chown=1000:1000 /build /app
FROM gradle:jdk21 AS builder
WORKDIR /build
COPY build.gradle* settings.gradle* ./
RUN gradle dependencies --no-daemon || true
COPY . .
RUN gradle build -x test --no-daemon \
&& rm -rf src/ gradle/ gradlew* build.gradle*
Run Command
The default run command depends on the build tool output:
Override with RUN_COMMAND or a Procfile:
web: java -jar target/myapp-1.0.jar
JVM Configuration
The following environment variables are set for production:
| Variable | Value |
|---|
JAVA_OPTS | -Dfile.encoding=UTF-8 -XX:MaxRAMPercentage=80.0 |
JAVA_TOOL_OPTIONS | -Dfile.encoding=UTF-8 |
Caching
Layer Caching
Dependencies are cached by copying build definition files before the full source:
| Build Tool | Cached Files |
|---|
| Maven | pom.xml |
| Gradle | build.gradle*, settings.gradle*, gradlew, gradle/ |
| Scenario | Dependency Install |
|---|
| First build | Runs |
| Source code change only | Cached |
| Build file change | Runs |
BUILD_CACHE_DIR
When BUILD_CACHE_DIR is set, build tool caches persist at:
| Cache Path | Contents |
|---|
/cache/maven | Maven repository (~/.m2/repository) |
/cache/gradle | Gradle caches and wrapper |
DHI Support
Docker Hardened Images are supported for Java builds.
| Stage | Image |
|---|
| Build | dhi.io/eclipse-temurin:{version}-jdk-dev |
| Runtime | dhi.io/eclipse-temurin:{version} |
DHI Notes
- Eclipse Temurin DHI images do not include Maven or Gradle. Build tools are installed via
apt-get in the builder stage.
- Runtime images are distroless (no shell, no
apt-get).
- The
nonroot user is used instead of the miget user.
- Version normalization applies:
1.8 becomes 8, 1.11 becomes 11.
Example with DHI
docker run --rm \
-v /path/to/java-app:/workspace/source \
-v /var/run/docker.sock:/var/run/docker.sock \
-e OUTPUT_IMAGE=my-java-app:latest \
-e USE_DHI=true \
miget/migetpacks:latest
Example
docker run --rm \
-v /path/to/java-app:/workspace/source \
-v /var/run/docker.sock:/var/run/docker.sock \
-e OUTPUT_IMAGE=my-java-app:latest \
miget/migetpacks:latest
With build cache
docker run --rm \
-v /path/to/java-app:/workspace/source \
-v /var/run/docker.sock:/var/run/docker.sock \
-v /tmp/build-cache:/cache \
-e OUTPUT_IMAGE=my-java-app:latest \
-e BUILD_CACHE_DIR=/cache \
miget/migetpacks:latest
