Java

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

Build Tool Detection

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

For Gradle projects:

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:

java -jar target/*.jar

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

Getting Started

Guides

Configuration

Languages

Deploying

Reference

Detection

Version Detection

Version Normalization

Build Process

Build Tool Detection

Gradle Wrapper

Generated Dockerfile

Run Command

JVM Configuration

Caching

Layer Caching

BUILD_CACHE_DIR

DHI Support

DHI Notes

Example with DHI

Example

With build cache

​Detection

​Version Detection

​Version Normalization

​Build Process

​Build Tool Detection

​Gradle Wrapper

​Generated Dockerfile

​Run Command

​JVM Configuration

​Caching

​Layer Caching

​BUILD_CACHE_DIR

​DHI Support

​DHI Notes

​Example with DHI

​Example

​With build cache

Detection

Version Detection

Version Normalization

Build Process

Build Tool Detection

Gradle Wrapper

Generated Dockerfile

Run Command

JVM Configuration

Caching

Layer Caching

BUILD_CACHE_DIR

DHI Support

DHI Notes

Example with DHI

Example

With build cache