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plugin_services.md

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title
Plugin Services

The IntelliJ Platform provides the concept of services.

A service is a plugin component loaded on demand, when your plugin calls the getService method of the ServiceManager class.

The IntelliJ Platform ensures that only one instance of a service is loaded even though the service is called several times. A service must have an implementation class which is used for service instantiation. A service may also have an interface class which is used to obtain the service instance and provides API of the service. The interface and implementation classes are specified in the plugin.xml file.

The IntelliJ Platform offers three types of services: application level services, project level services and module level services.

How to Declare a Service?

To declare a service, you can use the following extension points in the IDEA core:

  • applicationService: designed to declare an application level service.
  • projectService: designed to declare a project level service.
  • moduleService: designed to declare a module level service.

To declare a service:

  1. Add the appropriate child element (<applicationService>, <projectService> or <moduleService>) to the <extensions> section of the plugin.xml file.
  2. For the newly added child element, set the following attributes:
    • serviceInterface: specifies the service interface class.
    • serviceImplementation: specifies the service implementation class.

If serviceInterface isn't specified it's supposed to have the same value as serviceImplementation.

To clarify the service declaration procedure, consider the following fragment of the plugin.xml file:

<extensions defaultExtensionNs="com.intellij">
  <!-- Declare the application level service -->
  <applicationService serviceInterface="Mypackage.MyApplicationService" serviceImplementation="Mypackage.MyApplicationServiceImpl" />

  <!-- Declare the project level service -->
  <projectService serviceInterface="Mypackage.MyProjectService" serviceImplementation="Mypackage.MyProjectServiceImpl" />
</extensions>

Retrieving a service

To instantiate your service, in Java code, use the following syntax:

MyApplicationService applicationService = ServiceManager.getService(MyApplicationService.class);

MyProjectService projectService = ServiceManager.getService(project, MyProjectService.class);

MyModuleService moduleService = ModuleServiceManager.getService(module, MyModuleService.class);

Sample Plugin

This section allows you to download and install a sample plugin illustrating how to create and use a plugin service. This plugin has a project component implementing a service that counts the number of currently opened projects in the IDE. If this number exceeds the maximum allowed number of simultaneously opened projects, the plugin returns an error message and closes the most recently opened project.

To install and run the sample plugin

  • Download the included sample plugin project located here.
  • Start IntelliJ IDEA, on the starting page, click Open Project, and then use the Open Project dialog box to open the project max_opened_projects.
  • On the main menu, choose Run | Run or press Shift+F10.
  • If necessary, change the Run/Debug Configurations.