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Maven 101

Maven examples, created as part of a Maven 101 session given at eBay.
See: The session's slide deck

Examples

Useful Command Line Options

  • -h, --help
    Show the usage help page of the mvn command line tool
  • -U, --update-snapshots
    Force updating snapshots (overrides the once-a-day strategy)
  • -D, --define <arg> (e.g. -DskipTests)
    Define a system property, usually used for setting properties of plugins
  • -fae, --fail-at-end
    In multi module projects - fail only at the end of the run, after building all modules (instead of right after the first module with error)
  • -fn, --fail-never
    Do not fail the build at all
  • -pl, --projects <module>[,<module>]*
    Run a command only for specific projects (modules)
  • -P, --activate-profiles <profile>[,<profile>]*
    Activate a maven profile (which is defined in the pom or in the settings)

Useful Plugins

Help Plugin

The Apache Maven Help Plugin provides goals aimed at helping to make sense out of the build environment. It includes the ability to view the effective POM and settings files, after inheritance and active profiles have been applied, as well as a describe a particular plugin goal to give usage information.

Start with:

mvn help:help

A very helpful goal is the help:describe. It helps you get usage help information for other plugins, commands and goals.
For example, to see detailed help information on the help:describe goal itself, use:

mvn help:describe -Dplugin=help -Dgoal=describe -Ddetail

Another example - to see which plugin corresponds to the compile build lifecycle phase, use:

$ mvn help:describe -Dcmd=compile
...
[INFO] --- maven-help-plugin:3.1.0:describe (default-cli) @ my-minimal-project ---
[INFO] 'compile' is a phase corresponding to this plugin:
org.apache.maven.plugins:maven-compiler-plugin:3.1:compile

It is a part of the lifecycle for the POM packaging 'jar'. This lifecycle includes the following phases:
* validate: Not defined
* initialize: Not defined
...

It also prints the other build lifecycle phases and their corresponding plugins (if any).

Dependency Plugin

The Apache Maven Dependency Plugin provides the capability to manipulate artifacts. It can copy and/or unpack artifacts from local or remote repositories to a specified location.

The most useful goal of the dependency plugin is the dependency:tree. As its name implies, it prints the dependency tree of the project. A common use case is when you need to debug dependency issues.

For example, the following command prints a verbose dependency tree to a file named dependencies.txt:

mvn dependency:tree -Dverbose -DoutputFile=dependencies.txt

Versions Plugin

The Versions Maven Plugin is used when you want to manage the versions of artifacts in a project's POM. It is very useful for automating several parts of the version management. It is mostly useful in multi-module projects.

For example, a common use case is to set the version for all modules in a multi-module project. To set the project's new version to 1.2.0-SNAPSHOT, use:

mvn version:set -DnewVersion=1.2.0-SNAPSHOT

Build Helper Plugin

The Maven Build Helper Plugin contains various small independent goals to assist with the Maven build lifecycle.

Some very usefule tasks are:

  • Adding source folders
  • Adding resource folders
  • Adding test source folders
  • and more...