Snapcraft combines Java applications with the desired Java Runtime Environment and appropriate dependencies to create snaps for people to install on Linux.
What problems do snaps solve for Java applications?
Distributing a Java application for Linux and reaching the widest possible audience was complicated. Ensuring the end-user has the correct version of JRE/SDK and has their environment configured correctly are typical additional steps the user must undertake. When a Linux distribution changes the delivered JRE, this can be problematic for applications. Snapcraft ensures the correct JRE is shipped alongside the application at all times.
Here are some snap advantages that will benefit many Java projects:
- Simplify installation instructions, regardless of distribution, to
snap install myjavaapp.
- Directly control the delivery of automatic application updates.
How long will this guide take to complete?
Typically this guide will take around 20 minutes and will result in a working Java app in a snap. Once complete, you’ll understand how to package Java applications as snaps and deliver them to millions of Linux users. After making the snap available in the store, you’ll get access to installation metrics and tools to directly manage the delivery of updates to Linux users.
By way of an example, let’s take a look at how a simple Java application can be snapped using snapcraft.
Using a few lines of yaml and the snapcraft tool, a Java application, it’s dependencies and the correct JRE can be packaged as a snap. We’ll break this down.
name: freeplane version: '1.6.10' summary: Application for Mind Mapping, Knowledge and Project Management description: | Freeplane is a free and open source software application that supports thinking, sharing information and getting things done at work, in school and at home. The core of the software is tools for mind mapping (also known as concept mapping or information mapping) and using mapped information. confinement: devmode apps: freeplane: command: desktop-launch $SNAP/freeplane-1.6.10/freeplane.sh parts: freeplane: after: [desktop-glib-only] plugin: gradle source: . build: | export JAVA_HOME="/usr/lib/jvm/java-8-openjdk-amd64" gradle release -x test -x createGitTag install: | unzip DIST/freeplane_bin-*.zip -d $SNAPCRAFT_PART_INSTALL/ build-packages: - unzip - openjdk-8-jdk
snapcraft.yaml starts with a small amount of human-readable metadata, which usually can be lifted from the GitHub description or project README.md. This data is used in the presentation of your app in the Snap Store. The
summary: can not exceed 79 characters. You can use a pipe in the
description: key to declare a multi-line description.
name: freeplane version: '1.6.10' summary: Application for Mind Mapping, Knowledge and Project Management description: | Freeplane is a free and open source software application that supports thinking, sharing information and getting things done at work, in school and at home. The core of the software is tools for mind mapping (also known as concept mapping or information mapping) and using mapped information.
To get started we won’t confine this application. Unconfined applications, specified with
devmode, can only be released to the hidden “edge” channel where you and other developers can install them.
Parts define how to build your app. Parts can be anything: programs, libraries, or other assets needed to create and run your application. In this case we have two parts, the FreePlane source, and a remote
desktop-glib-only helper part. In other cases these can point to local directories, remote git repositories, or tarballs.
desktop-glib-only helper remote part will configure the runtime environment so that the application integrates well with the desktop environment. Other remote parts are available, and can be discovered via the
snapcraft search command.
The gradle plugin can build the application using standard parameters. In this case however we have overridden some gradle parameters (to disable testing, and prevent a new git tag being created), and set an appropriate
JAVA_HOME in a
build: script snippet. In the
install: script snippet we’re unpacking the built application into a directory which later gets incorporated into the final snap, defined by the
The build requires an appropriate JDK/JRE and the install step requires the addition of the
unzip command, so these are specified as
parts: freeplane: after: [desktop-glib-only] plugin: gradle source: . build: | export JAVA_HOME="/usr/lib/jvm/java-8-openjdk-amd64" gradle release -x test -x createGitTag install: | unzip DIST/freeplane_bin-*.zip -d $SNAPCRAFT_PART_INSTALL/ build-packages: - unzip - openjdk-8-jdk
Apps are the commands and services exposed to end users. If your command name matches the snap
name, users will be able run the command directly. If the names differ, then apps are prefixed with the snap
freeplane.command-name, for example). This is to avoid conflicting with apps defined by other installed snaps.
If you don’t want your command prefixed you can request an alias for it on the Snapcraft forum. These are set up automatically when your snap is installed from the Snap Store.
We have prefixed the FreePlane launch script with the
desktop-launch helper script, provided by the
desktop-glib-only remote part.
apps: freeplane: command: desktop-launch $SNAP/freeplane-1.6.10/freeplane.sh
If your application is intended to run as a service you simply add the line
daemon: simple after the command keyword. This will automatically keep the service running on install, update, and reboot.
Building the snap
You’ll first need to install snap support, and then install the snapcraft tool:
sudo snap install snapcraft --classic
If you have just installed snap support, start a new shell so your
PATH is updated to include
/snap/bin. You can then build this example yourself:
git clone https://github.com/snapcraft-docs/freeplane cd freeplane snapcraft
The resulting snap can be installed locally. This requires the
--dangerous flag because the snap is not signed by the Snap Store. The
--devmode flag acknowledges that you are installing an unconfined application:
sudo snap install freeplane_*.snap --devmode --dangerous
You can then try it out:
Removing the snap is simple too:
sudo snap remove freeplane
Share with your friends
To share your snaps you need to publish them in the Snap Store. First, create an account on dashboard.snapcraft.io. Here you can customize how your snaps are presented, review your uploads and control publishing.
You’ll need to choose a unique “developer namespace” as part of the account creation process. This name will be visible by users and associated with your published snaps.
Make sure the
snapcraft command is authenticated using the email address attached to your Snap Store account:
Reserve a name for your snap
You can publish your own version of a snap, provided you do so under a name you have rights to. You can register a name on dashboard.snapcraft.io, or by running the following command:
snapcraft register myjavasnap
Be sure to update the
name: in your
snapcraft.yaml to match this registered name, then run
Upload your snap
Use snapcraft to push the snap to the Snap Store.
snapcraft push --release=edge myjavasnap_*.snap
If you’re happy with the result, you can commit the snapcraft.yaml to your GitHub repo and turn on automatic builds so any further commits automatically get released to edge, without requiring you to manually build locally.