separate local download and install repositories using maven?

Question

I want to rebuild my project structure from scratch from time to time and want to purge the built repository in order to do that. However, I don't want to remove downloaded files from maven central and other repositories. Is there a simple way to tell maven to install my built artifacts into a separate repository, ie. other then the one used to store downloaded, external files?

I am NOT talking about deploy, just mvn install.

UPDATE

I found an alternate solution using only one local repository for both downloaded and self-built artifacts: the self-built ones are accompanied by files called "maven-metadata-local.xml", so I select the repository directories to purge based on the existence of that file now...

Answer 1

To formalize and expand on the “update” in the question (by the way you should not hesitate to answer your own question):

I came to a similar conclusion independently and include

find -L ~/.m2/repository \( -type d -name '*-SNAPSHOT' -prune -o -type f -name maven-metadata-local.xml \) -exec rm -rfv {} \;

in a general “cleanup” script that I run from time to time. Note that this differs from the ideal of install:install always going to a separate location in (at least) three ways:

• You have to remember to run this script, so in the meantime you could have a local repository “polluted” with things you built. On occasion this will mean that a build will work locally for you but will not work for others. (Or even fail only or you, or succeed for everyone but behave subtly differently.) This defeats the goal of reproducible builds, unless you have plenty of Internet bandwidth and are willing to run docker run --rm -v "$PWD":/usr/src/mymaven -w /usr/src/mymaven maven mvn clean install!
• If someone has intentionally deployed SNAPSHOTs to a shared repository, this script will delete them, so your next build will have to repeat the download.
• Local installs of release versions are not deleted. Now if these came from release:perform because you were the one cutting the release, that is not so bad—presumably the remote artifact is identical to your local copy anyway. Where this gets really evil is if, in the course of trying to debug some problem in someone else’s released artifact by rebuilding from sources with some diagnostic patches (say), you forget to edit pom.xml to use a SNAPSHOT or other distinguishing version, and install the result. Maven will never notice that your local copy differs from the official version, and you can get into weird situations months later. Of course this has never happened to me.

The latter two problems could perhaps be addressed with a more complicated script that parsed maven-metadata-*.xml files rather than assuming that all, and only, SNAPSHOTs were local builds. Or as the submitter hints at, just delete the whole version directory if maven-metadata-local.xml is present (distinguishing this somehow from the parent artifact directory, which will also have such a file, and resolver-status.properties too).

While it is nice that Maven 3 records some information about where artifacts in the local repository came from, it is not good enough. What I for one would really appreciate is if install:install always saved to a distinct location, so that the main local repository could be trusted to be purely a cache of downloads. Local artifact resolution would then prefer one or the other repository in case of conflict based on a command-line switch (after issuing a warning).

Answer 2

MINSTALL-126 enhancement about if this could be added to maven-install-plugin. In the mean time, see the following workaround, slightly extending what's proposed above, from a blog post I wrote on http://blog2.vorburger.ch/2016/06/maven-install-into-additional.html with some background about why this would be useful:

  <profiles>
    <profile>
      <activation>
        <property>
          <name>addInstallRepositoryPath</name>
        </property>
      </activation>
      <build>
        <plugins>
          <plugin>
            <artifactId>maven-install-plugin</artifactId>
            <executions>
              <execution>
                <id>additional-install</id>
                <phase>install</phase>
                <goals>
                  <goal>install-file</goal>
                </goals>
                <configuration>
                  <file>${project.build.directory}/${project.build.finalName}.jar</file>
                  <localRepositoryPath>${addInstallRepositoryPath}</localRepositoryPath>
                </configuration>
              </execution>
            </executions>
          </plugin>
        </plugins>
      </build>
    </profile>
  </profiles>

Answer 3

You cannot do that with the install goal. maven-install-plugin will install the artifact to the same local repository that is used to fetch downloaded artifacts from. By default, this is ${user.home}/.m2/repository. You change that by setting the system variable maven.repo.local to another location (or by telling Maven to use a specific settins.xml). However, at the moment, Maven can't be configured to install specific artifacts to a different local repository than where it is fetching downloaded artifacts.

A possible work-around would be to declare an execution of the install-file goal, bound to the install phase and declare it to install all of the artifacts you want to to the specified local repository.

<plugin>
    <artifactId>maven-install-plugin</artifactId>
    <version>2.5.2</version>
    <executions>
        <execution>
            <phase>install</phase>
            <goals>
                <goal>install-file</goal>
            </goals>
            <configuration>
                <file><!-- path to artifact to install --></file>
                <pomFile><!-- path to POM of artifact --></pomFile>
                <localRepositoryPath><!-- path to repository you want to install to --></localRepositoryPath>
            </configuration>
        </execution>
    </executions>
</plugin>