Merge pull request #1159 from carlossg/maven

Update maven docs

maven/content.md

@@ -6,28 +6,59 @@
 
 # How to use this image
 
-## Create a Dockerfile in your Maven project
+You can run a Maven project by using the Maven Docker image directly, passing a Maven command to `docker run`:
 
-```dockerfile
-FROM %%IMAGE%%:3.2-jdk-7-onbuild
-CMD ["do-something-with-built-packages"]
+```console
+$ docker run -it --rm --name my-maven-project -v "$(pwd)":/usr/src/mymaven -w /usr/src/mymaven %%IMAGE%%:3.3-jdk-8 mvn clean install
+```
+
+## Building local Docker image (optional)
+
+This is a base image that you can extend, so it has the bare minimum packages needed. If you add custom package(s) to the `Dockerfile`, then you can build your local Docker image like this:
+
+```console
+$ docker build --tag my_local_%%IMAGE%%:3.5.2-jdk-8 .
 ```
 
-Put this file in the root of your project, next to the pom.xml.
+# Reusing the Maven local repository
+
+The local Maven repository can be reused across containers by creating a volume and mounting it in `/root/.m2`.
 
-This image includes multiple ONBUILD triggers which should be all you need to bootstrap. The build will `COPY . /usr/src/app` and `RUN mvn install`.
+	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
 
-You can then build and run the image:
+Or you can just use your home .m2 cache directory that you share e.g. with your Eclipse/IDEA:
 
 ```console
-$ docker build -t my-maven .
-$ docker run -it --name my-maven-script my-maven
+$ 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.
+
+```dockerfile
+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
+
+```dockerfile
+COPY settings.xml /usr/share/maven/ref/
 ```
 
-## Run a single Maven command
+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 many simple projects, you may find it inconvenient to write a complete `Dockerfile`. In such cases, you can run a Maven project by using the Maven Docker image directly, passing a Maven command to `docker run`:
+For example, to run as user `1000` mounting the host' Maven repo
 
 ```console
-$ docker run -it --rm --name my-maven-project -v "$PWD":/usr/src/mymaven -w /usr/src/mymaven %%IMAGE%%:3.2-jdk-7 mvn clean install
+$ 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
 ```