Easily package your Maven Java application with the Nix package manager.

• How to use this
  • Generating the Nix dependencies file
  • Building a Maven repository
  • Sample Derivation
• How does it work?
• Development

How to use this

Generating the Nix dependencies file

In the same spirit of bundix, mvn2nix creates a Nix set with the transitive closure of all dependencies required by the application.

$ nix run -f https://github.com/fzakaria/mvn2nix/archive/master.tar.gz \
        --command mvn2nix > dependencies.nix

$ head dependencies.nix
{
  "junit:junit:pom:3.8.1" = {
    url = "https://repo.maven.apache.org/maven2/junit/junit/3.8.1/junit-3.8.1.pom";
    layout = "junit/junit/3.8.1/junit-3.8.1.pom";
    sha256 = "e68f33343d832398f3c8aa78afcd808d56b7c1020de4d3ad8ce47909095ee904";
  };
  "org.sonatype.forge:forge-parent:pom:10" = {
    url = "https://repo.maven.apache.org/maven2/org/sonatype/forge/forge-parent/10/forge-parent-10.pom";
    layout = "org/sonatype/forge/forge-parent/10/forge-parent-10.pom";
    sha256 = "c14fb9c32b59cc03251f609416db7c0cff01f811edcccb4f6a865d6e7046bd0b";

You can then use this to download all the necessary dependencies to run your application.

Building a Maven repository

Now that you have a nix dependencies file; we can re-construct a Maven repository using Nix!

let mvn2nix = import (fetchTarball https://github.com/fzakaria/mvn2nix/archive/master.tar.gz) { };
in
mvn2nix.buildMavenRepsitory { dependencies = import ./dependencies.nix; }

This creates a /nix/store path which is a Maven repository that can be used, such as in mvn package --offline -Dmaven.repo.local=${mavenRepository}

$ tree /nix/store/2ps43297g5nii2k15kfy8z46fam51d8x-buildMavenRepository | head

/nix/store/2ps43297g5nii2k15kfy8z46fam51d8x-buildMavenRepository
├── com
│   └── google
│       ├── code
│       │   └── findbugs
│       │       └── jsr305
│       │           └── 3.0.2
│       │               └── jsr305-3.0.2.jar -> /nix/store/w20lb1dk730v77qis8l6sjqpljwkyql7-jsr305-3.0.2.jar
│       ├── errorprone
│       │   └── error_prone_annotations

Sample Derivation

{ pkgs ? import <nixpkgs> {} }:
let
  mvn2nix = import
    (fetchTarball "https://github.com/fzakaria/mvn2nix/archive/add-pom.tar.gz")
    { };
  buildMavenRepository = mvn2nix.buildMavenRepository;
  mavenRepository = buildMavenRepository { dependencies = import ./dependencies.nix; };
inherit (pkgs) lib stdenv jdk11_headless maven makeWrapper;
inherit (stdenv) mkDerivation;
in mkDerivation rec {
  pname = "my-artifact";
  version = "0.01";
  name = "${pname}-${version}";
  src = lib.cleanSource ./.;

  buildInputs = [ jdk11_headless maven makeWrapper ];
  buildPhase = ''
    echo "Building with maven repository ${mavenRepository}"
    mvn package --offline -Dmaven.repo.local=${mavenRepository}
  '';

  installPhase = ''
    # create the bin directory
    mkdir -p $out/bin

    # create a symbolic link for the lib directory
    ln -s ${mavenRepository}/.m2 $out/lib

    # copy out the JAR
    # Maven already setup the classpath to use m2 repository layout
    # with the prefix of lib/
    cp target/${name}.jar $out/

    # create a wrapper that will automatically set the classpath
    # this should be the paths from the dependency derivation
    makeWrapper ${jdk11_headless}/bin/java $out/bin/${pname} \
          --add-flags "-jar $out/${name}.jar"
  '';
}

How does it work?

mvn2nix relies on maven-invoker; which fires off Maven in a separate JVM process.

Maven is executed with a temporary ephemeral local repository for the given goals provided (defaults to package). The local repository is than traversed, and each encountered file is recorded in the dependencies list.

mvn2nix includes an example output & derivation that builds itself!

Development

If you are running mvn2nix from this repository, you can do so with nix-build

$ nix-build

./result/bin/mvn2nix > example/dependencies.nix

If you want to test buildMavenRepository you can run:

$ nix-build -A buildMavenRepository --arg dependencies "import ./dependencies.nix"