Example Java app¶

This how-to guide covers the steps, decisions, and implementation details that are unique when crafting a Java-based snap. We’ll work through the aspects unique to Java apps by examining an existing recipe.

The process of developing a snap for a Java app builds on top of JRE, making it possible to adapt and integrate an app’s existing build tooling and dependencies into the crafting process.

Example recipe for Cal¶

The following code comprises the recipe of a Java project, liquidctl. This project is both a driver and a CLI tool for power and cooling components in PCs.

Cal recipe

name: fcal
version: "2.7.1"
summary: Command line calendar display
description: |
  fCal is a command line calendar utility. It will display a calendar on
  the command line with any month/year requested. Defaults to the current
  year. fCal can also display local holidays. See help.
grade: stable
confinement: strict
base: core22

title: fCal
website: https://github.com/frossm/cal/issues
issues: https://github.com/frossm/ca
license: MIT

# Enable faster LZO compression
compression: lzo

# Ignore useless library warnings
lint:
  ignore:
    - library

apps:
  fcal:
    command: cal-wrapper
    plugs:
      - network

parts:
  wrapper:
    plugin: dump
    source: snap/local
    source-type: local

  library:
    plugin: maven
    source: https://github.com/frossm/library.git
    source-type: git
    source-tag: "v2023.12.03"
    maven-parameters:
      - install
    build-packages:
      - maven
      - openjdk-11-jdk-headless

  cal:
    plugin: maven
    source: https://github.com/frossm/cal.git
    source-branch: master
    source-type: git
    after:
      - library
    build-packages:
      - maven
      - openjdk-11-jdk-headless
    stage-packages:
      - openjdk-11-jre-headless
    override-prime: |
      snapcraftctl prime
      rm -vf usr/lib/jvm/java-11-openjdk-*/lib/security/blacklisted.certs

Add a part written in Java¶

cal:
  plugin: maven
  source: https://github.com/frossm/cal.git
  source-branch: master
  source-type: git
  after:
    - library
  build-packages:
    - maven
    - openjdk-11-jdk-headless
  stage-packages:
    - openjdk-11-jre-headless
  override-prime: |
    snapcraftctl prime
    rm -vf usr/lib/jvm/java-11-openjdk-*/lib/security/blacklisted.certs

Java parts are built with the Maven plugin. The plugin can build the app using standard parameters. It requires a pom.xml file at the root of the source tree.

To declare a Java part:

Declare the general part keys, such as source, override-build, organize, and so on.
Set plugin: maven.
For build-packages, list the following dependencies:
```
- maven
- openjdk-11-jdk-headless
```
For stage-packages, add openjdk-11-jre-headless as a dependency.