How do I configure Maven for offline development?

Question

You can run maven in offline mode mvn -o install. Of course any artifacts not available in your local repository will fail. Maven is not predicated on distributed repositories, but they certainly make things more seamless. Its for this reason that many shops use internal mirrors that are incrementally synced with the central repos.

In addition, the mvn dependency:go-offline can be used to ensure you have all of your dependencies installed locally before you begin to work offline.

If you have a PC with internet access in your LAN, you should install a local Maven repository.

I recommend Artifactory Open Source. This is what we use in our organization, it is really easy to setup.

Artifactory acts as a proxy between your build tool (Maven, Ant, Ivy, Gradle etc.) and the outside world.

It caches remote artifacts so that you don’t have to download them over and over again.

It blocks unwanted (and sometimes security-sensitive) external requests for internal artifacts and controls how and where artifacts are deployed, and by whom.

After setting up Artifactory you just need to change Maven's settings.xml in the development machines:

<?xml version="1.0" encoding="UTF-8"?>
<settings xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd" xmlns="http://maven.apache.org/SETTINGS/1.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <mirrors>
    <mirror>
      <mirrorOf>*</mirrorOf>
      <name>repo</name>
      <url>http://maven.yourorganization.com:8081/artifactory/repo</url>
      <id>repo</id>
    </mirror>
  </mirrors>
  <profiles>
    <profile>
      <repositories>
        <repository>
          <snapshots>
            <enabled>false</enabled>
          </snapshots>
          <id>central</id>
          <name>libs-release</name>
          <url>http://maven.yourorganization.com:8081/artifactory/libs-release</url>
        </repository>
        <repository>
          <snapshots />
          <id>snapshots</id>
          <name>libs-snapshot</name>
          <url>http://maven.yourorganization.com:8081/artifactory/libs-snapshot</url>
        </repository>
      </repositories>
      <pluginRepositories>
        <pluginRepository>
          <snapshots>
            <enabled>false</enabled>
          </snapshots>
          <id>central</id>
          <name>plugins-release</name>
          <url>http://maven.yourorganization.com:8081/artifactory/plugins-release</url>
        </pluginRepository>
        <pluginRepository>
          <snapshots />
          <id>snapshots</id>
          <name>plugins-snapshot</name>
          <url>http://maven.yourorganization.com:8081/artifactory/plugins-snapshot</url>
        </pluginRepository>
      </pluginRepositories>
      <id>artifactory</id>
    </profile>
  </profiles>
  <activeProfiles>
    <activeProfile>artifactory</activeProfile>
  </activeProfiles>
</settings>

We used this solution because we had problems with internet access in our development machines and some artifacts downloaded corrupted files or didn't download at all. We haven't had problems since.

You have two options for this:

1.) make changes in the settings.xml add this in first tag

<localRepository>C:/Users/admin/.m2/repository</localRepository>

2.) use the -o tag for offline command.

mvn -o clean install -DskipTests=true
mvn -o jetty:run

Maven needs the dependencies in your local repository. The easiest way to get them is with internet access (or harder using other solutions provided here).

So assumed that you can get temporarily internet access you can prepare to go offline using the maven-dependency-plugin with its dependency:go-offline goal. This will download all your project dependencies to your local repository (of course changes in the dependencies / plugins will require new internet / central repository access).

Before going offline you have to make sure that everything is in your local repo, which is required while working offline. Running "mvn dependency:go-offline" for the project(s)/pom(s), you intend to work on, will reduce the efforts to achieve this.

But it´s usually not the whole story, because dependency:go-offline will only download the "bare build" plugins (go-offline / resolve-plugins does not resolve all plugin dependencies). So you have to find a way to download deploy / test / site plugins (and maybe others) and their dependencies into your repo.

Furthermore dependency:go-offline does not download the pom´s artifact itself, so you have to dependency:copy it if required.

Sometimes - as MaDa wrote - you do not know, what you will need, while being offline, which makes it pretty impossible to have a "sufficient" repo.

Anyway having a properly filled repo you only have to add "<offline>true</offline>" to Maven´s settings.xml to go offline.

Do not change the Maven profile (id) you used to fill your repo, while being offline. Maven recognizes the downloaded artifacts in its metadata with an "identity", which is bound to the profile id.

Sadly dependency:go-offline hasn't worked for me as it didn't cached everything, ie. POMs files and other implicitly mention dependencies.

The workaround has been to specify a local repository location, either within settings.xml file with <localRepository>...</localRepository> or by running mvn with -Dmaven.repo.local=... parameter. After initial project build, all necessary artifacts should be cached, and then you can reference repository location the same ways, while running Maven build in offline mode (mvn -o ...).

If you're using IntelliJ, you can simply go to Preferences -> Build, Execution, Deployment -> Build Tools -> Maven and check/uncheck Work offline.