Caching Maven with Docker and Kotlin - maven

Question

I am trying to warm up my Docker + Maven cache before building a Kotlin project.
As suggested by many Maven/Docker threads, my docker file looks like this:
COPY pom.xml .
RUN mvn dependency:go-offline
COPY ./src/ src/
RUN mvn package
The thought is that if I change a file in the ./src directory, I want docker cache to skip maven's lengthy dependency download page.
My problem is that the mvn package command still downloads alot of files.
I tried to use mvn -o package (maven offline flag) to diagnose what dependencies are missing, but it just complains that it cannot download dependencies. But I would have expected that the dependencies would allready be downloaded in the previous step. Here are the errors that I get with the "-o" flag:
Step 8/13 : RUN mvn dependency:go-offline
---> Using cache
---> 0334facb9cc9
Step 9/13 : COPY ./src/ src/
---> Using cache
---> 27149a191017
Step 10/13 : RUN mvn -o package
---> Running in 5183eced32ca
Warning: JAVA_HOME environment variable is not set.
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building auth 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) # auth ---
[WARNING] The POM for org.apache.maven:maven-core:jar:2.0.6 is missing, no dependency information available
[WARNING] The POM for org.apache.maven:maven-monitor:jar:2.0.6 is missing, no dependency information available
[WARNING] The POM for org.codehaus.plexus:plexus-utils:jar:2.0.5 is missing, no dependency information available
[WARNING] The POM for org.apache.maven.shared:maven-filtering:jar:1.1 is missing, no dependency information available
[WARNING] The POM for org.codehaus.plexus:plexus-interpolation:jar:1.13 is missing, no dependency information available
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.882 s
[INFO] Finished at: 2019-07-12T07:02:23+00:00
[INFO] Final Memory: 13M/174M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-resources-plugin:2.6:resources (default-resources) on project auth: Execution default-resources of goal org.apache.maven.plugins:maven-resources-plugin:2.6:resources failed: Plugin org.apache.maven.plugins:maven-resources-plugin:2.6 or one of its dependencies could not be resolved: The following artifacts could not be resolved: org.apache.maven:maven-plugin-api:jar:2.0.6, org.apache.maven:maven-project:jar:2.0.6, org.apache.maven:maven-profile:jar:2.0.6, org.apache.maven:maven-artifact-manager:jar:2.0.6, org.apache.maven:maven-repository-metadata:jar:2.0.6, org.apache.maven:maven-plugin-registry:jar:2.0.6, org.apache.maven:maven-core:jar:2.0.6, org.apache.maven:maven-artifact:jar:2.0.6, org.apache.maven:maven-settings:jar:2.0.6, org.apache.maven:maven-model:jar:2.0.6, org.apache.maven:maven-monitor:jar:2.0.6, classworlds:classworlds:jar:1.1-alpha-2, org.codehaus.plexus:plexus-utils:jar:2.0.5, org.apache.maven.shared:maven-filtering:jar:1.1, org.codehaus.plexus:plexus-interpolation:jar:1.13: Cannot access central (https://repo.maven.apache.org/maven2) in offline mode and the artifact org.apache.maven:maven-plugin-api:jar:2.0.6 has not been downloaded from it before. -> [Help 1

Answer 1

Try following mvn commands, it saved me from the maven error.
RUN mvn --batch-mode --errors --strict-checksums --threads 1C \
org.apache.maven.plugins:maven-dependency-plugin:3.0.2:go-offline
RUN mvn --batch-mode --errors --offline package

Answer 2

From what I gathered from various sources go-offline not always handles caching packages in a correct way, leaving some of them outside of the local repository (see pull request on GitHub).
In my case, the standard mvn dependency:go-offline used go-offline 2.8 and returned errors. I then tried running mvn org.apache.maven.plugins:maven-dependency-plugin:3.2.0:go-offline but I still had some issues with different packages.
What worked for me was using a different "go-offline" plugin available at GitHub.
Using
mvn de.qaware.maven:go-offline-maven-plugin:resolve-dependencies
finally did the job.