intellij-sdk-code-samples/basics/plugin_structure/plugin_services.md

title
Plugin 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.

Light Service

Service that is not going to be overridden. No need to register it in a plugin.xml.

To register: annotate class using @Service annotation. If service is written in Java and not Kotlin, mark class as final.

Restrictions:

• constructor injection is not supported (since it is deprecated), but project level service can define constructor that accepts Project, and module level Module.
• if service it is a PersistentStateComponent, roaming must be disabled (roamingType is set to RoamingType.DISABLED).
• service class must be final.

How to Declare a Service?

To declare a service, you can use the following extension points in the IntelliJ Platform:

• com.intellij.applicationService: designed to declare an application level service.
• com.intellij.projectService: designed to declare a project level service.
• com.intellij.moduleService: designed to declare a module level service. Consider not using module services because it can lead to increased memory usage for a project with a lot of modules.

To declare a service:

1. In your project, open the context menu of the destination package and click New (or press Alt+Insert).
2. In the New menu, choose Plugin DevKit and click Application Service, Project Service or Module Service depending on the type of service you need to use.
3. In the dialog box that opens, you can specify service interface and implementation, or just a service class if you uncheck Separate interface from implementation check box.

The IDE will generate new Java interface and class (or just a class if you unchecked Separate interface from implementation check box) and register the new service in plugin.xml file.

Note

Declaring a service via New context menu is available since version 2017.3.

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>

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

Retrieving a service

Getting service doesn't need read action and can be performed from any thread. If service requested from several threads, it will be initialized in the first thread and another threads will be blocked until service is not fully initialized.

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

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

MyProjectService projectService = project.getService(MyProjectService.class)

In Kotlin code you can use convenient methods:

MyApplicationService applicationService = service<MyApplicationService>()

MyProjectService projectService = project<service<MyProjectService>()

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.