Configuration

Avoid repeating flags by creating a jbundle.toml in your project root.

Configuration File

# jbundle.toml

java_version = 21
target = "linux-x64"
jvm_args = ["-Xmx512m", "-XX:+UseZGC"]
build_args = ["-PeaJdkBuild=false"]
profile = "cli"
shrink = true
appcds = true
crac = false
compact_banner = false

# Gradle multi-project options
gradle_project = "app"
modules = ["java.base", "java.sql"]
java_home = "/usr/lib/jvm/java-21"
jlink_runtime = "./build/jlink"

All fields are optional.

Options

Field	Type	Default	Description
java_version	integer	21	JDK version to bundle
target	string	current platform	Target platform (linux-x64, macos-aarch64, etc.)
jvm_args	array	[]	JVM arguments passed at runtime
build_args	array	[]	Extra arguments passed to the build tool
profile	string	"server"	JVM profile ("cli" or "server")
shrink	boolean	false	Shrink uberjar by removing non-essential files
appcds	boolean	true	Enable AppCDS for faster startup
crac	boolean	false	Enable CRaC checkpoint (Linux only)
compact_banner	boolean	false	Use a compact banner in the wrapper
gradle_project	string	—	Gradle subproject to build (for multi-project)
modules	array	—	Manual module list (bypasses jdeps detection)
java_home	string	—	Path to existing JDK installation (skips download). Falls back to JAVA_HOME env var.
jlink_runtime	string	—	Path to existing jlink runtime to reuse

Precedence

Configuration values are resolved in this order (highest to lowest):

1. CLI flags — --java-version 17 overrides everything

2. jbundle.toml — Project-level defaults

3. Internal defaults — Built-in values

Examples

CLI Tool

Optimized for fast startup:

# jbundle.toml
java_version = 21
profile = "cli"
jvm_args = ["-Xmx256m"]

Microservice

Standard server configuration with custom GC:

# jbundle.toml
java_version = 21
profile = "server"  # Important: use "server" when specifying custom GC
jvm_args = ["-Xmx1g", "-XX:+UseZGC"]

Note: When using a custom garbage collector like ZGC, always use profile = "server". The "cli" profile includes -XX:+UseSerialGC, and the JVM cannot use multiple GCs simultaneously. jbundle will detect this conflict and fail with a helpful error message.

Cross-Platform Build

Targeting Linux from macOS:

# jbundle.toml
java_version = 21
target = "linux-x64"

Maximum Performance (Linux)

With CRaC for instant startup:

# jbundle.toml
java_version = 21
profile = "cli"
crac = true

Gradle Multi-Project

For complex projects like JabRef:

# jbundle.toml
gradle_project = "jabkit"
java_version = 21
profile = "cli"
jvm_args = ["-Xmx1g"]

With Custom Modules

When jdeps detection is insufficient:

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

Custom Build Arguments

Pass extra flags to the build tool (e.g., Gradle project properties):

# jbundle.toml
gradle_project = "app"
build_args = ["-PeaJdkBuild=false", "-PprojVersion=1.2.3"]

Works with any build system. Arguments are appended to the build command.

Reusing Existing Runtime

Skip jlink if you have a pre-built runtime:

# jbundle.toml
jlink_runtime = "./build/jlink"

Reusing Local JDK

Skip JDK download by reusing an existing installation:

# jbundle.toml
java_home = "/usr/lib/jvm/java-21"

If java_home is not set in the config or CLI, jbundle automatically checks the JAVA_HOME environment variable.

Environment Variables

Variable	Description
JAVA_HOME	Path to existing JDK installation (used when --java-home and java_home config are not set)
RUST_LOG	Logging level (error, warn, info, debug, trace)

For debugging, set RUST_LOG to control jbundle's logging:

# Show debug output
RUST_LOG=debug jbundle build --input . --output ./dist/app

# Show only warnings
RUST_LOG=warn jbundle build --input . --output ./dist/app