PF4J Maven

Thin JAR plugin support for PF4J with Maven dependency resolution.

A proof-of-concept for pf4j/pf4j#208 - plugins as Maven artifacts with automatic dependency resolution.

Overview

Instead of packaging plugins as fat JARs or ZIPs with bundled dependencies, this approach allows plugins to be specified as Maven coordinates. Dependencies are resolved and downloaded automatically at runtime using Maven Resolver.

Traditional PF4J:

plugins/
  my-plugin.jar (fat jar with all dependencies inside)

PF4J Maven:

plugins.txt:
  com.example:my-plugin:jar:plugin:1.0.0

# Dependencies resolved automatically from Maven repositories

Features

• Plugins specified as Maven coordinates (groupId:artifactId:jar:classifier:version)
• Automatic transitive dependency resolution
• Uses local Maven repository (~/.m2/repository) and Maven Central
• Caches resolved artifacts to avoid redundant downloads

How It Works

1. Application reads plugin coordinates from plugins.txt
2. MavenPluginManager resolves each artifact using Maven Resolver
3. Plugin JAR is copied to plugins/<artifactId>/
4. Dependencies (excluding provided and test scope) are copied to plugins/<artifactId>/lib/
5. Standard PF4J loading takes over

Usage

Basic Usage

// Use the builder to create MavenPluginManager
PluginManager pluginManager = MavenPluginManagerBuilder.create().build();
pluginManager.loadPlugins();
pluginManager.startPlugins();

List<Greeting> greetings = pluginManager.getExtensions(Greeting.class);
for (Greeting greeting : greetings) {
    System.out.println(">>> " + greeting.getGreeting());
}

Builder Configuration

The builder supports various configuration options:

PluginManager pluginManager = MavenPluginManagerBuilder.create()
    .pluginsRoot(Paths.get("my-plugins"))           // custom plugins directory
    .localRepository(Paths.get("/custom/m2/repo"))  // custom local Maven repo
    .addRemoteRepository("jitpack", "https://jitpack.io")  // additional repo
    .includeMavenCentral(true)                      // include Maven Central (default)
    .processLooseJars(true)                         // process loose JARs (default)
    .skipExistingDependencies(true)                 // skip if lib/ exists (default)
    .build();

Extending MavenPluginManager

For advanced customization, extend MavenPluginManager:

class CustomPluginManager extends MavenPluginManager {
    @Override
    protected PluginFactory createPluginFactory() {
        return new CustomPluginFactory();
    }
}

plugins.txt:

org.pf4j.demo:pf4j-maven-demo-plugin1:jar:plugin:1.0.0-SNAPSHOT
# org.pf4j.demo:pf4j-maven-demo-plugin2:jar:plugin:1.0.0-SNAPSHOT

Demo

A working demo is available in the demo folder.

Quick run:

./run-demo.sh      # Linux/Mac
run-demo.bat       # Windows

Output:

>>> Whazzup
>>> Welcome

Project Structure

pf4j-maven/          # Core library
  MavenPluginManager
  MavenPluginManagerBuilder
  MavenPluginLoader
  MavenUtils

demo/
  app/               # Demo application
  api/               # Shared plugin API
  plugins/           # Demo plugins
    plugin1/         # welcome-plugin (uses commons-lang)
    plugin2/         # hello-plugin

Requirements

• Java 8+
• Maven 3.6+

Related

• PF4J - Plugin Framework for Java
• Issue #208 - Original proposal for this feature