Bundling a JRE

Java apps need a Java Runtime Environment to run. Typically this is installed by the user and hopefully already available when they go to run your app. Unfortunately users may not have Java installed and there are differences between JREs that can cause problems with your app. These can be difficult for users to explain and worse, difficult for them to fix themselves. Also, you may require, as a minimum, a certain JRE version.

The solution is to bundle a JRE with your app. This way you know exactly what users will be running and users will have fewer problems and they will not have to install a JVM.

Packaging

There are a number of tools available for bundling a JRE:

jpackage

Jpackage is a modern solution for providing native packaging options on Windows, MacOS and Linux introduced with JEP-343. It can be used to create an EXE that starts your bundled application via an embedded JRE.

See this guide for more information on how to use it. A video version can be found here.

Packr

A packaging tool created and maintained by the libGDX team. Take a look at the repository if you are interested in using it.

Parcl

A Gradle plugin that performs similar actions as launch4j. See its README for instructions.

launch4j

– seems to be no longer maintained –

MacOS Specifics

If you’re planning to deploy to MacOS as well, notarization (MacOS 10.15+) can be an issue. See here on how to notarize your libGDX app.

Reducing Size

There are a number of files and classes that can be removed from the JRE to reduce the size. Below is a list of files to delete from the Windows JRE. Other platforms are very similar, though you may need classes on some platforms but not others (eg, xml classes are needed on Linux to use java.util.preferences). This list leaves Swing intact, if you don’t need Swing the size could be reduced further.

**.diz
**.exe except javaw.exe
bin\client\
lib\applet\
lib\charsets.jar
lib\ext\localedata.jar
lib\management\
lib\management-agent.jar
lib\zi\
lib\rt.jar\com\sun\org\
lib\rt.jar\com\sun\xml\
lib\rt.jar\com\sun\corba\
lib\rt.jar\com\sun\media\
lib\rt.jar\com\sun\jndi\
lib\rt.jar\com\sun\imageio\
lib\rt.jar\com\sun\jmx\
lib\rt.jar\com\sun\rowset\
lib\rt.jar\com\sun\java\util\
lib\rt.jar\javax\imageio\
lib\rt.jar\javax\management\
lib\rt.jar\javax\print\
lib\rt.jar\javax\naming\
lib\rt.jar\javax\sound\
lib\rt.jar\javax\sql\
lib\rt.jar\javax\xml\
lib\rt.jar\javax\swing\plaf\nimbus\
lib\rt.jar\javax\swing\text\html\
lib\rt.jar\org\
lib\rt.jar\sun\applet\
lib\rt.jar\sun\management\
lib\rt.jar\sun\rmi\
lib\rt.jar\sun\security\jgss\
lib\rt.jar\sun\security\krb5\
lib\rt.jar\sun\security\tools\
lib\resources.jar\com\sun\corba\
lib\resources.jar\com\sun\imageio\
lib\resources.jar\com\sun\jndi\
lib\resources.jar\com\sun\org\
lib\resources.jar\com\sun\rowset\
lib\resources.jar\com\sun\servicetag\
lib\resources.jar\com\sun\xml\
lib\jsse.jar\sun\security\ssl\

To make this list I went through the files and JARs sorting by largest size first. I then deleted the largest files that looked like that were not needed and ran my app to make sure everything still works.

This list reduces the JRE size to about 36MB. Note that for faster start up the JRE JARs are not compressed. After zipping the entire JRE, the size is reduced to about 13.5MB. If Swing packages are also removed from rt.jar, the zipped size goes down to about 9.8MB.