Making Standalone Java apps

Back in high school days, I learned how Java programs could work flawlessly across different machines without the need for any additional compilation - Write once, run anywhere. One of our laptops had a 64-bit Ubuntu installed while the other one had a 32-bit Windows 7. I tested out on a few more platforms and realized one particular hurdle that constantly popped up: It was necessary to have Java installed beforehand, which most OSs didn't ship by default. So here's a post about how you could make your apps truly standalone.

Bundling a JRE

A bundled JRE would allow your app to run just as it would with a user-side runtime. Because of the flawless compatibility, this method is preferred by many popular desktop apps including JetBrains IDEs and Minecraft. Bundling a complete JRE has been the traditional solution for making standalone apps. There's also a variety of tools that will help you create a proper package using this method. However, it also produces the most bloated distributable, as you're bundling the entire runtime even if you use only a few parts of the standard library. Here are some of the free OpenJDK builds you can use for bundling:

There aren't many significant downsides to this, other than bloating your package size. Gradle or Maven could also be easily configured to bundle a JRE along with your distributable ZIP. One of the goals of my GSoC project was to bundle a JRE with the Terasology Launcher, so that it runs without hassle.

Customized JRE

Since Java 9, the jlink tool can be used to assemble a custom Java runtime based on your module dependencies. This would result in a minimized JRE with just enough modules to run your app perfectly. However, it's not available in JDK 8 or older, which still has a significant developer population. Nevertheless, jlink is your best bet for modern standalone Java apps that don't want any compromise with its massive ecosystem.

Helpful tools

Manual JRE bundling is a tedious job, so here are some common tools that can help you create a standalone package for your apps. These differ by the supported package formats and platforms:

libGDX packr: CLI tool supporting Windows, OS X and Linux. Can minimize JRE 8 and older too.
install4j: GUI tool supporting Windows, OS X and Linux.
launch4j: GUI tool for creating Windows installer.
parcl: Gradle plugin similar to packr.
javapackager: Maven plugin supporting multiple package formats like deb, rpm, msi, dmg, and zip.
snapcraft: Creates snap packages that can run across major Linux distros.

Priyadarshi Raj

Priyadarshi Raj