Extension Points

NOTE See Plugin Extensions for using extension points in your plugin.

By defining extension points in your plugin, you can allow other plugins to extend your plugin's functionality. There are two types of extension points:

• Interface extension points allow other plugins to extend your plugins with code. When you define an interface extension point, you specify an interface, and other plugins will provide classes implementing that interface. You'll then be able to invoke methods on those interfaces.
• Bean extension points allow other plugins to extend your plugins with data. You specify the fully qualified name of an extension class, and other plugins will provide data that will be turned into instances of that class.

Declaring Extension Points

You can declare extensions and extension points in the plugin configuration file plugin.xml, within the <extensions> and <extensionPoints> sections.

To declare extension points in your plugin, add an <extensionPoints> section to your plugin.xml. Then insert a child element <extensionPoint> that defines the extension point name and the name of a bean class or an interface that is allowed to extend the plugin functionality in the name, beanClass and interface attributes, respectively.

myPlugin/META-INF/plugin.xml

<idea-plugin>
  <id>my.plugin</id>

  <extensionPoints>
    <extensionPoint name="myExtensionPoint1"
                    beanClass="com.myplugin.MyBeanClass"/>

    <extensionPoint name="myExtensionPoint2"
                    interface="com.myplugin.MyInterface"/>
  </extensionPoints>

</idea-plugin>

The name attribute assigns a unique name for this extension point. It will be prefixed with the plugin's <id> automatically.

The beanClass attribute sets a bean class that specifies one or several properties annotated with the @Attribute annotation. The interface attribute sets an interface the plugin that contributes to the extension point must implement.

The area attribute determines the scope in which the extension will be instantiated. As extensions should be stateless, it is not recommended to use non-default. Must be one of IDEA_APPLICATION for Application (default), IDEA_PROJECT for Project, or IDEA_MODULE for Module scope.

The plugin that contributes to the extension point will read those properties from the plugin.xml file.

Sample

To clarify this, consider the following sample MyBeanClass bean class used in the above plugin.xml file:

myPlugin/src/com/myplugin/MyBeanClass.java

public class MyBeanClass extends AbstractExtensionPointBean {

  @Attribute("key")
  public String key;

  @Attribute("implementationClass")
  public String implementationClass;

  public String getKey() {
    return key;
  }

  public String getClass() {
    return implementationClass;
  }
}

TIP See Extension properties code insight on how to provide smart completion/validation.

For above extension points usage in anotherPlugin would look like this (see also Declaring Extensions):

anotherPlugin/META-INF/plugin.xml

<idea-plugin>
  <id>another.plugin</id>

  <!-- declare dependency on plugin defining extension point -->
  <depends>my.plugin</depends>

  <!-- use "my.plugin" namespace -->
  <extensions defaultExtensionNs="my.plugin">
    <myExtensionPoint1 key="someKey"
                       implementationClass="another.some.implementation.class"/>

    <myExtensionPoint2 implementation="another.MyInterfaceImpl"/>
  </extension>

</idea-plugin>

Using Extension Points

To refer to all registered extension instances at runtime, declare an ExtensionPointName passing in the fully-qualified name matching its declaration in plugin.xml.

myPlugin/src/com/myplugin/MyExtensionUsingService.java

public class MyExtensionUsingService {

    private static final ExtensionPointName<MyBeanClass> EP_NAME =
      ExtensionPointName.create("my.plugin.myExtensionPoint1");

    public void useExtensions() {
      for (MyBeanClass extension : EP_NAME.getExtensionList()) {
        String key = extension.getKey();
        String clazz = extension.getClass();
        // ...
      }
    }
}

A gutter icon for the ExtensionPointName declaration allows navigating to the corresponding <extensionPoint> declaration in plugin.xml.