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Joel Gillman

Using Docker to build and compile a Java Minecraft plugin

docker command line minecraft java gradle

The Problem

I hate the inventory system in Minecraft. It's usually fine for a bit but eventually it's just a pile of unorganized crap and I can never find anything. Plus seeing all my chests of items all messy drives me nuts.

There's a great plugin called Inventory Tweaks which I've used in the past but I'm playing the latest version of Minecraft (1.9 at the moment) and there isn't a stable version of Inventory Tweaks!

It's open sourced on Github but there's no nightly or dev builds available. I'm a developer and I know command-line-buildy-compiley-things but I don't want to install an entire Java development environment. It'll take up space on my machine and I'll have to deal with updates, incompatibilities, and conflicts... It's just a lot more work than I'm willing to put in just for a single Minecraft plugin.

Luckily I have Docker installed and know enough to plod my way through most of the basics.

The First Try

This is the originally way I did it. It worked, but it was slower and took just over 5 minutes to compile.

cd ~/Code
git clone git@github.com:Inventory-Tweaks/inventory-tweaks.git
cd inventory-tweaks
docker run -v ~/Code/inventory-tweaks:/app qlik/gradle build

Easy right? Docker takes care of creating a contained Java development environment with gradle which is needed to build the plugin.

After it finishes running one of the final lines of output should say BUILD SUCCESSFUL along with the total time.

I have never done any Java development or compiling before so I had to do a bit of digging to figure out that it would output to build/libs. Sure enough, taking a peek in the build/libs folder revealed three fresh new .jar files! I popped InventoryTweaks-1.61-dev.jar into my Minecraft folder's mods folder and it worked like a charm.

Make It Faster

While the original way I did it worked, using a volume (-v) to add the project source makes the whole build process kind of slow. If you've used synced folders with Vagrant you have likely seen a similar issue. I'm not actually doing any development, I just want a dev build of the plugin!

I wrote a small Dockerfile that simply ADDs the project source to the Docker container and defaults to the build command.

Dockerfile:

FROM qlik/gradle

ADD . /app
CMD ["build"]

Assuming I'm still in the project folder I can build a new image for gradle with the settings I've added in the Dockerfile.

docker build -t mc-inventory .

Finally, I re-run docker run this time tweaked and new options.

docker run --rm -v ~/Downloads/inventory-tweaks:/app/build/libs mc-inventory
  • --rm Removes the container after it's done running. Since I just want the end product I don't really care about having the container lay around afterwards.
  • -v This time I'm only adding a volume that syncs with /app/build/libs and I've set it to a folder in my local machine's Downloads folder.
  • The image name changed from qlik/gradle to mc-inventory which is the new image created with docker build
  • Don't need build at the very end any more because it's defined in the Dockerfile.