Components
Plugin Components are a legacy feature supported for compatibility with plugins created for older versions of the IntelliJ Platform. Plugins using Components do not support dynamic loading (the ability to install, update, and uninstall plugins without restarting the IDE).
Plugin Components are defined in the <application-components>, <project-components>, and <module-components> sections in a Plugin Configuration File.
Migration
To migrate existing code from Components to more modern APIs, please see the following guidelines.
Manage State
To manage some state or logic that is only needed when the user performs a specific operation, use a Service.
Persisting State
To store the state of your plugin at the application or project level, use a Service, and implement the PersistentStateComponent interface. See Persisting State of Components for details.
Subscribing to Events
To subscribe to events, use a listener or create an extension for a dedicated extension point (for example, com.intellij.editorFactoryListener) if one exists for the event to subscribe to.
Application Startup
Plugin code should only be executed when projects are opened (see Project Open) or when the user invokes an action of a plugin. If this cannot be avoided, add a listener subscribing to the AppLifecycleListener topic. See also Running Tasks Once.
To execute an activity in background on IDE startup (e.g., to warm up caches), use PreloadingActivity.
Project Open
To execute code when a project is being opened, use one of these two extensions:
com.intellij.postStartupActivity
StartupActivity for immediate execution on EDT. Implement DumbAware to indicate activity can run in background thread (in parallel with other such tasks).
com.intellij.backgroundPostStartupActivity
StartupActivity.Background for execution with 5 seconds delay in background thread (2019.3 or later).
Any long-running or CPU intensive tasks should be made visible to users by using ProgressManager.run(Task.Backgroundable). Access to indices must be wrapped with DumbService, see also General Threading Rules.
See also Running Tasks Once.
Project and Application Close
To execute code on project closing or application shutdown, implement the Disposable interface in a Service and place the code in the dispose() method. Alternatively, use Disposer.register() passing a Project or Application service instance as the parent argument (see Choosing a Disposable Parent).