Gradle Multi-Project

jbundle automatically detects and handles Gradle multi-project builds with multiple application subprojects.

How It Works

When jbundle detects settings.gradle.kts (or .gradle), it:

1. Parses included subprojects
2. Scans each for the application plugin
3. Extracts mainClass, mainModule, and addModules configuration
4. Offers selection or builds all with --all

Detection

jbundle looks for these patterns in build.gradle.kts:

plugins {
    id("application")
}

application {
    mainClass.set("com.example.Main")
}

And module configuration:

javaModulePackaging {
    addModules.add("jdk.incubator.vector")
}

Single Subproject

Interactive Selection

When multiple application subprojects exist:

jbundle build --output ./dist/app

Multiple application subprojects found:
  [1] app - com.example.App
  [2] cli - com.example.Cli
  [3] server - com.example.Server

Tip: Add 'gradle_project = "app"' to jbundle.toml to skip this prompt

Select subproject [1-3]:

CLI Flag

Skip the prompt with --gradle-project:

jbundle build --output ./dist/app --gradle-project app

Configuration File

Set default in jbundle.toml:

gradle_project = "app"

All Subprojects

Build every application subproject with --all:

jbundle build --output ./dist --all

Each binary is placed in {output}/{subproject-name}:

./dist/
├── app
├── cli
└── server

Module Handling

Automatic Detection

jbundle combines:

1. jdeps analysis — Scans JAR for required modules
2. Gradle config — Extracts addModules.add(...) from build files

Both are merged and deduplicated for the jlink runtime.

Manual Override

Bypass automatic detection with --modules:

jbundle build --output ./dist/app \
  --gradle-project app \
  --modules java.base,java.sql,jdk.incubator.vector

Or in configuration:

# jbundle.toml
gradle_project = "app"
modules = ["java.base", "java.sql", "jdk.incubator.vector"]

Reusing Existing Runtime

If Gradle already built a jlink image, skip the jlink step:

jbundle build --output ./dist/app \
  --gradle-project app \
  --jlink-runtime ./app/build/jlink

Common locations jbundle checks:

• {subproject}/build/jlink/
• {subproject}/build/image/
• {subproject}/build/jpackage/images/app-image/

Build Process

For subprojects, jbundle runs:

1. :{subproject}:shadowJar (preferred, produces fat JAR)
2. Falls back to :{subproject}:build if shadowJar unavailable

Then looks for JAR in:

• {subproject}/build/libs/*-all.jar
• {subproject}/build/libs/*-uber.jar
• {subproject}/build/libs/*.jar

Configuration Reference

New options for multi-project builds:

CLI Flags

Flag	Description
--gradle-project <NAME>	Build specific subproject
--all	Build all application subprojects
--build-args <ARGS>	Extra arguments passed to Gradle (e.g., -P flags)
--modules <LIST>	Manual module list (comma-separated)
--jlink-runtime <PATH>	Reuse existing jlink runtime

jbundle.toml

# Subproject to build by default
gradle_project = "app"

# Manual module override
modules = ["java.base", "java.sql"]

# Extra build arguments
build_args = ["-PeaJdkBuild=false"]

# Reuse existing runtime
jlink_runtime = "./build/jlink"

Examples

Simple Multi-Project

# Interactive selection
jbundle build --output ./dist/app

# Specific subproject
jbundle build --output ./dist/cli --gradle-project cli

# All at once
jbundle build --output ./dist --all

With Custom Modules

jbundle build \
  --output ./dist/app \
  --gradle-project app \
  --modules java.base,java.desktop,java.sql

Reusing Gradle's jlink

# First, run Gradle's jlink task
./gradlew :app:jlink

# Then use it with jbundle
jbundle build \
  --output ./dist/app \
  --gradle-project app \
  --jlink-runtime ./app/build/image

Troubleshooting

"No application subproject found"

Check that subprojects have the application plugin applied:

plugins {
    id("application")
}

"Subproject 'x' not found"

Verify the subproject name matches what's in settings.gradle.kts:

include("app")  // Use "app", not ":app"

Module errors at runtime

If the app fails with java.lang.module errors, modules are missing. Use --modules to add them:

jbundle build --modules java.base,java.sql,java.logging,...

shadowJar not available

If your project doesn't use Shadow plugin, ensure the regular build produces a fat JAR with all dependencies bundled.