d daedalus

Java

Building a Java App

daedalus supports Java apps via Maven and Gradle. It detects a Java project by the presence of pom.xml (Maven) or build.gradle / build.gradle.kts (Gradle).

Detection

File Build system Entrypoint strategy
pom.xml Maven -jar target/*.jar or -cp with mainClass
build.gradle Gradle -jar build/libs/*.jar or -cp with mainClass

The builder parses <mainClass> from:

  • maven-jar-plugin configuration
  • exec-maven-plugin configuration
  • spring-boot-maven-plugin configuration
  • MANIFEST.MF inside the built JAR (fallback)
  • application { mainClass.set(...) } in Gradle DSL

Prerequisites

  • A JDK installed (java on PATH)
  • The app must be built before packaging:
    • Maven: mvn package
    • Gradle: gradle build

Build

# Maven project
daedalus build ./my-java-app -o my-java-app.de

# Gradle project
daedalus build ./my-gradle-app -o my-gradle-app.de

The builder:

  1. detects the java runtime and locates the JAR in target/ or build/libs/;
  2. parses the mainClass from build config or JAR manifest;
  3. embeds the java interpreter and its shared libraries;
  4. packages the JAR into the app layer;
  5. compresses and assembles the .de.

Entrypoint

The launcher runs:

/opt/java/bin/java -jar /app/my-app.jar

or if mainClass is known but no fat JAR exists:

/opt/java/bin/java -cp /app/classes com.example.Main

Spring Boot

Spring Boot apps are detected via spring-boot-maven-plugin or spring-boot-gradle-plugin. The builder reads the mainClass from the plugin configuration.

cd my-spring-app
mvn package
daedalus build . -o my-spring-app.de
./my-spring-app.de

Environment variables

JAVA_OPTS="-Xmx512m" ./my-java-app.de
PORT=9000 ./my-java-app.de

Known limitations

  • The JDK is embedded as a runtime layer (not a JRE). Final binary is ~100-200MB depending on the JDK version. A JRE-only mode is planned.
  • GraalVM native-image support is not yet implemented.
  • Multi-module Gradle builds: only the main module's JAR is packaged.
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