#205: org.projectforge.plugins.core.AbstractPlugin (ServiceLoader)

Architecture

Content

org.projectforge.plugins.ihk.IHKPlugin

This file sits at the standard Java ServiceLoader path META-INF/services/{fully-qualified-interface-name}. When ProjectForge's plugin scanner invokes ServiceLoader.load(AbstractPlugin.class), the JVM reads all such files from the classpath, instantiates each listed class, and calls initialize() on each plugin instance.

Plugin Discovery Flow

1. Spring application context starts.
2. PFPluginService (or equivalent plugin scanner) calls ServiceLoader.load(AbstractPlugin.class).
3. JVM finds META-INF/services/org.projectforge.plugins.core.AbstractPlugin in each plugin JAR or classpath entry.
4. For each fully-qualified class name in those files, the class is loaded and instantiated via its no-arg constructor.
5. The AbstractPlugin base class constructor registers the plugin's metadata (ID, name, description).
6. The plugin scanner calls initialize(), where IHKPlugin performs its DAO, web, menu, right, and i18n registrations.

Design Decisions

• Standard Java SPI: ProjectForge uses java.util.ServiceLoader rather than Spring's @Component scanning for plugin discovery. This allows plugins to be loaded from external JARs dropped into a plugin directory, independent of Spring's component scan base packages.
• One file, one class: Each plugin provides exactly one implementation class per service file. The IHK plugin registers only IHKPlugin.
• Separate from Spring bean scanning: While IHKPlugin itself is not a Spring bean, the components it wires (via WicketSupport.get()) are Spring-managed. This hybrid approach keeps plugin lifecycle separate from Spring context lifecycle.
• Also serves as ServiceLoader for domain objects: This same file pattern is critical for Hibernate domain object discovery — without it, the plugin's persistent entities would not be found by the ORM scanner.

Git History

50d5d8926 wip: META-INF/services needed for plugins (Service loader)
07b80966b wip: PFPluginService (PluginConfig) -> PluginInfo
45cad02e9 IHK-Plugin added (Will replace "Ihk-Export"-Plugin)