content.md

What is Maven?

Apache Maven is a software project management and comprehension tool. Based on the concept of a project object model (POM), Maven can manage a project's build, reporting and documentation from a central piece of information.

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How to use this image

You can run a Maven project by using the Maven Docker image directly, passing a Maven command to docker run:

$ docker run -it --rm --name my-maven-project -v "$(pwd)":/usr/src/mymaven -w /usr/src/mymaven %%IMAGE%%:3.3-jdk-8 mvn clean install

Building local Docker image (optional)

This is a base image that you can extend, so it has the bare minimum packages needed. If you add custom package(s) to the Dockerfile, then you can build your local Docker image like this:

$ docker build --tag my_local_%%IMAGE%%:3.5.2-jdk-8 .

Reusing the Maven local repository

The local Maven repository can be reused across containers by creating a volume and mounting it in /root/.m2.

$ docker volume create --name maven-repo
$ docker run -it -v maven-repo:/root/.m2 %%IMAGE%% mvn archetype:generate # will download artifacts
$ docker run -it -v maven-repo:/root/.m2 %%IMAGE%% mvn archetype:generate # will reuse downloaded artifacts

Or you can just use your home .m2 cache directory that you share e.g. with your Eclipse/IDEA:

$ docker run -it --rm -v "$PWD":/usr/src/mymaven -v "$HOME/.m2":/root/.m2 -v "$PWD/target:/usr/src/mymaven/target" -w /usr/src/mymaven %%IMAGE%% mvn clean package  

Packaging a local repository with the image

The $MAVEN_CONFIG dir (default to /root/.m2) could be configured as a volume so anything copied there in a Dockerfile at build time is lost. For that reason the dir /usr/share/maven/ref/ exists, and anything in that directory will be copied on container startup to $MAVEN_CONFIG.

To create a pre-packaged repository, create a pom.xml with the dependencies you need and use this in your Dockerfile. /usr/share/maven/ref/settings-docker.xml is a settings file that changes the local repository to /usr/share/maven/ref/repository, but you can use your own settings file as long as it uses /usr/share/maven/ref/repository as local repo.

COPY pom.xml /tmp/pom.xml
RUN mvn -B -f /tmp/pom.xml -s /usr/share/maven/ref/settings-docker.xml dependency:resolve

To add your custom settings.xml file to the image use

COPY settings.xml /usr/share/maven/ref/

For an example, check the tests dir

Running as non-root

Maven needs the user home to download artifacts to, and if the user does not exist in the image an extra user.home Java property needs to be set.

For example, to run as user 1000 mounting the host' Maven repo

$ docker run -v ~/.m2:/var/maven/.m2 -ti --rm -u 1000 -e MAVEN_CONFIG=/var/maven/.m2 %%IMAGE%% mvn -Duser.home=/var/maven archetype:generate