Public Service Announcement: With packr v2.0, command line interfaces to both packr.jar and the native executable have changed, as well as the format of minimize profiles! If you upgrade from a previous version, please read this documentation again to make sure you've updated your configuration(s) accordingly.


Packages your JAR, assets and a JVM for distribution on Windows, Linux and Mac OS X, adding a native executable file to make it appear like a native app. Packr is most suitable for GUI applications, such as games made with libGDX.


The latest build is available for download here.


You point packr at your JAR file(s) containing your code and assets, some configuration parameters, and a URL or local file location to a JDK build for your target platform.

Invoking packr from the command line may look like this:

java -jar packr.jar \
     --platform mac \
     --jdk \
     --executable myapp \
     --classpath myapp.jar \
     --removelibs myapp.jar \
     --mainclass \
     --vmargs Xmx1G \
     --resources src/main/resources path/to/other/assets \
     --minimizejre soft \
     --output out-mac
Parameter Meaning
platform one of "windows32", "windows64", "linux32", "linux64", "mac"
jdk directory, ZIP file, or URL to ZIP file of an OpenJDK or Oracle JDK build containing a JRE. Prebuild OpenJDK packages can be found at You can also specify a directory to an unpacked JDK distribution. E.g. using ${java.home} in a build script
executable name of the native executable, without extension such as ".exe"
classpath file locations of the JAR files to package
removelibs (optional) file locations of JAR files to remove native libraries which do not match the target platform. See below for details.
mainclass the fully qualified name of the main class, using dots to delimit package names
vmargs list of arguments for the JVM, without leading dashes, e.g. "Xmx1G"
resources (optional) list of files and directories to be packaged next to the native executable
minimizejre minimize the JRE by removing directories and files as specified by an additional config file. Comes with a few config files out of the box. See below for details on the minimization config file.
output the output directory
cachejre (optional) An optional directory to cache the result of JRE extraction and minimization. See below for details.
icon (optional, OS X) location of an AppBundle icon resource (.icns file)
bundle (optional, OS X) the bundle identifier of your Java application, e.g. ""
verbose prints more status information during processing, which can be useful for debugging
help shows the command line interface help

Alternatively, you can put all the command line arguments into a JSON file which might look like this:

    "platform": "mac",
    "jdk": "/Users/badlogic/Downloads/",
    "executable": "myapp",
    "classpath": [
    "removelibs": [
    "mainclass": "",
    "vmargs": [
    "resources": [
    "minimizejre": "soft",
    "output": "out-mac"

You can then invoke the tool like this:

java -jar packr.jar my-packr-config.json

It is possible to combine a JSON configuration and the command line. For single options, the command line parameter overrides the equivalent JSON option. For multi-options (e.g. classpath or vmargs), the options are merged.

This is an example which overrides the output folder and adds another VM argument. Note that the config file name is delimited by -- because the option prior to it, --vmargs, allows multiple arguments:

java -jar packr.jar --output target/out-mac --vmargs Xms256m -- my-packr-config.json

Finally, you can use packr from within your Java code. Just add the JAR file to your project, either manually, or via the following Maven dependency:


To invoke packr, you need to create an instance of PackrConfig and pass it to Packr.pack():

PackrConfig config = new PackrConfig();
config.platform = PackrConfig.Platform.Windows32;
config.jdk = "/User/badlogic/Downloads/";
config.executable = "myapp";
config.classpath = Arrays.asList("myjar.jar");
config.removePlatformLibs = config.classpath;
config.mainClass = "";
config.vmArgs = Arrays.asList("Xmx1G");
config.minimizeJre = "soft";
config.outDir = new"out-mac");

new Packr().pack(config);



A standard OpenJDK JRE weighs about 90 mb unpacked. Packr helps you cut down on that size, thus also reducing the download size of your app.

To minimize the JRE that is bundled with your app, you have to specify a minimization configuration file via the minimizejre flag you supply to Packr. A minimization configuration is a JSON file containing paths to files and directories within the JRE to be removed.

As an example, have a look at the soft profile configuration:

  "reduce": [
      "archive": "jre/lib/rt.jar",
      "paths": [
  "remove": [
      "platform": "*",
      "paths": [
      "platform": "windows",
      "paths": [

This configuration will unpack rt.jar, remove all the listed packages and classes in com.sun.* and sun.*, then repack rt.jar again. By default, the JRE uses zero-compression on its JAR files to make application startup a little faster, so this step will reduce the size of rt.jar substantially.

Then, rhino.jar (about 1.1MB) and, in case of a Windows JRE, all executable files in jre/bin/ and the folder jre/bin/client/ will be removed.

Packr comes with two such configurations out of the box, soft and hard. The hard profile removes a few more files, and repacks some additional JAR files.

There's also a new, experimental configuration, oraclejre8, which reduces size of an Oracle 8 JRE following Oracle's redistribution rules described here. It also repacks JAR files, reducing (unpacked) JRE size from about 180 mb to 70 mb. This version is pretty much untested, so please use with care!

The "removelibs" option

Minimization aside, packr can remove all dynamic libraries which do not match the target platform from your project JAR file(s):

platform files removed
Windows *.dylib, *.so
Linux *.dll, *.dylib
MacOS *.dll, *.so

This step is optional. If you don't need it, just remove the configuration parameter to speed up packr.


Extracting and minimizing a JRE can take quite some time. If the cachejre option is used, the result of these operations is cached in the given folder, and can be reused in subsequent runs of packr.

As of now, packr doesn't do any elaborate checks to validate the content of this cache folder. So if you update the JDK, or change the minimize profile, you need to empty or remove this folder manually to force a change.


When packing for Windows, the following folder structure will be generated




Mac OS X

         icons.icns [if config.icon is set]

You can further modify the Info.plist to your liking, e.g. add icons, a bundle identifier etc. If your output folder has the .app extension it will be treated as an application bundle by Mac OS X.

Executable command line interface

By default, the native executables forward any command line parameters to your Java application's main() function. So, with the configurations above, ./myapp -x y.z is passed as String[] {"-x", "y.z" }).

The executables themselves expose an own interface, which has to be enabled explicitly by passing -c or --cli as the very first parameter. In this case, the special delimiter parameter -- is used to separate the native CLI from parameters to be passed to Java. In this case, the example above would be equal to ./myapp -c [arguments] -- -x y.z.

Try ./myapp -c --help for a list of available options. They are also listed here.

Note: On Windows, the executable does not show any output by default. Here you can use myapp.exe -c --console [arguments] to spawn a console window, making terminal output visible.

Building from source code

If you want to modify the Java code only, it's sufficient to invoke Maven.

mvn clean package

This will create a packr-VERSION.jar file in target which you can invoke as described in the Usage section above.

If you want to compile the native executables, please follow these instructions. Each of the build scripts will create executable files for the specific platform and copy them to src/main/resources.


License & Contributions

The code is licensed under the Apache 2 license. By contributing to this repository, you automatically agree that your contribution can be distributed under the Apache 2 license by the author of this project. You will not be able to revoke this right once your contribution has been merged into this repository.


Distributing a bundled JVM has security implications, just like bundling any other runtimes like Mono, Air, etc. Make sure you understand the implications before deciding to use this tool. Here's a discussion on the topic.