---
title: Plugin Services
---

*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://github.com/JetBrains/intellij-community/blob/master/platform/core-api/src/com/intellij/openapi/components/ServiceManager.java)
class.
*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.
*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">
      </applicationService>

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

### How It Works?

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 a 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 *Shift + F10*.

*  If necessary, change the [Run/Debug Configurations](http://www.jetbrains.com/idea/help/run-debug-configuration-plugin.html).