What is the maven-shade-plugin used for, and why would you want to relocate Java packages?

java

maven-plugin

dependency-management

uber-jar

byAlex Kataev·Mar 11, 2025

The maven-shade-plugin performs the magic trick of condensing numerous jars into one uber-jar, effectively saying goodbye to classpath squabbles. It also relocates classes, altering their packages, to forestall conflicts due to identical class names from diverse libraries.

Example:

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-shade-plugin</artifactId>
  <executions>
    <execution>
      <goals><goal>shade</goal></goals>
      <configuration>
        <relocations>
          <relocation>
            <pattern>conflict.package</pattern>
            <shadedPattern>resolved.package</shadedPattern>
          </relocation>
        </relocations>
      </configuration>
    </execution>
  </executions>
</plugin>

The snippet above tells conflict.package to pack its bag and move in with resolved.package within the uber-jar, side-stepping potential class conflicts. It's like sending a misbehaving kid to boarding school!

Using the shade cloak: when and why

Sleep easy knowing maven-shade-plugin is there for you during:

Deployments: ride the wave of convenience as your application runs with all dependencies onboard, no left-behinds.
Conflict Looming: Having two-faced dependencies? Different versions trying to pull you apart? Shade plugin will play the peacemaker isolating them. Keep your friends close, and your enemies in different namespaces.
AWS Lambda: Deliver your code and dependencies in one tidy package to AWS Lambda. No runtime surprises!
Standalone Apps: Want your app to stand tall, independent, and without any shared jars? It's your time to shine with the shade plugin.

An uber-jar is no hobbit: beware the pitfalls

Despite their handy nature, uber-jars come with caution labels:

Size Matters: These jars might bloat faster than you expect, carrying excess luggage (read: unnecessary files). Use <filters> to exclude the non-essentials.
Library Queer: Developing a library destined for other projects? Steer away from uber-jars; they hate nested JAR dilemmas.
Not Your Silver Bullet: Some conflicts run deeper than class naming and packaging. Just like high school drama, understanding your dependencies is unavoidable!

How to be the shade master: best practices

When in the realm of shading:

Single-Use Potion: Ensure your shaded uber-jar knows it's a lone ranger, not a dependency for other Maven projects.
Dependency Marriage: Shading sometimes means signing up for life with a particular version of a library. Be prepared to update manually, come rain or shine!
A Friend in Need: If Maven shading feels like a square peg in a round hole, consider tools like JarJar to relocate packages. Remember the time-tested adage: debug, or die trying!

Meet the wizard: advanced shading techniques

Level up your shading game for these situations:

Refactoring Hogwarts: Merge multiple projects or modules under a new umbrella, avoiding classpath conflicts and introducing the new sorted houses!
Precise Potions: Don't trust the unstable upstream versions? Here's your chance to embed a specific version of libraries into your application.
Creating Dementors: Maven Shade Plugin got your back to create custom classloaders within the uber-jar, allowing you to load classes dynamically at runtime.

Defeating the dementors: potential challenges

Prepare for these notorious villains:

Double Casting Spells: If an upstream dependency is also a ’shade' enthusiast, double shading might lead to unexpected outcomes.
Resource Discovery: If resources in META-INF/services are mislocated or mismatched, you can stumble upon the infamous Service Provider Interface (SPI) issues.
Reflected Engorgements: If your code is one to lean on reflection, renaming classes and packages might break its legs unless handled with care.