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Trusted By

• Netflix Spinnaker - Continuous delivery platform
• Facebook Buck (Java version) - Build system
• Huawei Cloud - Real-time data processing and scoring systems (MRS - MapReduce Service)
• Eclipse Foundation - Connected Services Platform (ECSP) for automotive software-defined vehicles
• Appsmith - Low-code application platform
• Halo CMS - Modern content management

View more projects…

A plugin is a way for a third party to extend the functionality of an application. A plugin implements extension points declared by application or other plugins. Also, a plugin can define extension points.

NOTE: Starting with version 0.9 you can define an extension directly in the application jar (you’re not obligated to put the extension in a plugin - you can see this extension as a default/system extension). See WhazzupGreeting for a real example.

Features/Benefits

With PF4J you can easily transform a monolithic java application in a modular application.
PF4J is an open source (Apache license) lightweight (around 100 KB) plugin framework for java, with minimal dependencies (only slf4j-api) and very extensible (see PluginDescriptorFinder and ExtensionFinder).

Why Choose PF4J?

• Enterprise-proven: Powers Netflix Spinnaker and Facebook Buck
• Lightweight: Only ~100KB with minimal dependencies
• Simple: No XML configuration, pure Java
• Alternative to OSGi: Easy to learn and implement

Practically, PF4J is a microframework that aims to keep the core simple but extensible. PF4J also provides a community-driven ecosystem of extensions.

Components

• Plugin is the base class for all plugins types. Each plugin is loaded into a separate class loader to avoid conflicts.
• PluginManager is used for all aspects of plugins management (loading, starting, stopping). You can use a built-in implementation as JarPluginManager, ZipPluginManager, DefaultPluginManager (it’s a JarPluginManager + ZipPluginManager) or you can implement a custom plugin manager starting from AbstractPluginManager (implement only factory methods).
• PluginLoader loads all information (classes) needed by a plugin.
• ExtensionPoint is a point in the application where custom code can be invoked. It’s a java interface marker.
  Any java interface or abstract class can be marked as an extension point (implements ExtensionPoint interface).
• Extension is an implementation of an extension point. It’s a java annotation on a class.

PLUGIN = a container for EXTENSION POINTS and EXTENSIONS + lifecycle methods (start, stop, delete)

A PLUGIN is similar with a MODULE from other systems. If you don’t need lifecycle methods (hook methods for start, stop, delete) you are not forced to supply a plugin class (the PluginClass property from the plugin descriptor is optional). You only need to supply some description of plugin (id, version, author, …) for a good tracking (your application wants to know who supplied the extensions or extensions points).

Java version

The current minimum Java version required to build PF4J should be 9, but the runtime Java version can be 8 since the artifact is a multi-release jar.