---
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](https://upsource.jetbrains.com/idea-community/file/1731d054af4ca27aa827c03929e27eeb0e6a8366/platform/core-api/src/com/intellij/openapi/components/ServiceManager.java) 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 the interface and implementation classes specified in the `plugin.xml` file. The service implementation class is used for service instantiation.

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.

Note that the interface and implementation classes can be the same.

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

```xml
<extensions defaultExtensionNs="com.intellij">
  <!-- Declare the application level service -->
  <applicationService serviceInterface="Mypackage.MyServiceInterfaceClass" serviceImplementation="Mypackage.MyServiceImplClass" />

  <!-- Declare the project level service -->
  <projectService serviceInterface="Mypackage.MyProjectServiceInterfaceClass" serviceImplementation="Mypackage.MyProjectServiceImplClass" />
</extensions>
```

## Retrieving a service

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

```java
MyServiceImplClass service = ServiceManager.getService(MyServiceImplClass.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 *IntelliJ IDEA*. 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.

<!-- TODO Replace with other plugin URL when available-->

**To install and run the sample plugin**

* Click [here](/attachments/MaxOpenedProjects.zip) to download the .Zip archive that contains the sample plugin project.
* Extract all files from the .Zip archive to a separate folder.
* Start *IntelliJ IDEA*, on the starting page, click *Open Project*, and then use the *Open Project* dialog box to open the downloaded project *MaxOpenedProjects*.
* On the main menu, choose *Run \| Run* or press <kbd>Shift</kbd>+<kbd>F10</kbd>.
* If necessary, change the [Run/Debug Configurations](http://www.jetbrains.com/idea/help/run-debug-configuration-plugin.html).