Persisting State of Components

The IntelliJ Platform provides an API that allows components or services to persist their state between restarts of the IDE. The API allows for persisting simple key-value entries and complex state classes.

Using `PersistentStateComponent`

The PersistentStateComponent interface allows for persisting state classes and gives the most flexibility for defining the values to be persisted, their format, and storage location.

To use it:

mark a service (project or application-level service for storing project or application data, respectively) as implementing the PersistentStateComponent interface
define the state class
specify the storage location using @State

Note that instances of extensions can't persist their state by implementing PersistentStateComponent. If an extension needs to have a persistent state, define a separate service responsible for managing that state.

Implementing the `PersistentStateComponent` Interface

The easiest way to implement a persistent state component in Kotlin is extending SimplePersistentStateComponent, which implements PersistentStateComponent.

SimplePersistentStateComponent is parameterized by a subclass of BaseState. BaseState provides a set of handy property delegates, which make it easy to create properties with default values. In addition, delegates track property modifications internally, which helps decrease calling PersistentStateComponent.getState() by the platform.

It is recommended to create separate classes for a component and its state:

@Service
@State(...)
class MySettings : SimplePersistentStateComponent<MyState>(MyState())

class MyState : BaseState() {
  var value by string()
}

The implementation of PersistentStateComponent must be parameterized with the type of state class. The state class can either be a separate class, or the class implementing PersistentStateComponent.

Persistent Component with Separate State Class

In this case, the state class instance is typically stored as a field in the PersistentStateComponent class. When the state is loaded from the storage, it is assigned to the state field (see loadState()):

@Service
@State(...)
class MySettings implements PersistentStateComponent<MySettings.State> {

  static class State {
    public String value;
  }

  private State myState = new State();

  @Override
  public State getState() {
    return myState;
  }

  @Override
  public void loadState(State state) {
    myState = state;
  }
}

Using a separate state class is the recommended approach.

Persistent Component Being a State Class

In this case, getState() returns the component itself, and loadState() copies properties of the state loaded from storage to the component instance:

@Service
@State(...)
class MySettings implements PersistentStateComponent<MySettings> {

  public String stateValue;

  @Override
  public MySettings getState() {
    return this;
  }

  @Override
  public void loadState(MySettings state) {
    XmlSerializerUtil.copyBean(state, this);
  }
}

Implementing the State Class

The implementation of PersistentStateComponent works by serializing public fields, annotated private fields (see also Customizing the XML format of persisted values), and bean properties into an XML format.

To exclude a public field or bean property from serialization, annotate the field or getter with @Transient.

Note that the state class must have a default constructor. It should return the component's default state: the one used if there is nothing persisted in the XML files yet.

State class should have an equals() method, but state objects are compared by fields if it is not implemented.

The following types of values can be persisted:

numbers (both primitive types, such as int, and boxed types, such as Integer)
booleans
strings
collections
maps
enums

For other types, extend Converter. See the example below.

Converter Example

class LocalDateTimeConverter extends Converter<LocalDateTime> {
  public LocalDateTime fromString(@NotNull String value) {
    long epochMilli = Long.parseLong(value);
    ZoneId zoneId = ZoneId.systemDefault();
    return Instant.ofEpochMilli(epochMilli)
        .atZone(zoneId)
        .toLocalDateTime();
  }

  public String toString(LocalDateTime value) {
    ZoneId zoneId = ZoneId.systemDefault();
    long toEpochMilli = value.atZone(zoneId)
        .toInstant()
        .toEpochMilli();
    return Long.toString(toEpochMilli);
  }
}

Define the converter above in @OptionTag or @Attribute:

class State {
  @OptionTag(converter = LocalDateTimeConverter.class)
  public LocalDateTime dateTime;
}

Defining the Storage Location

To specify where precisely the persisted values are stored, add the @State annotation to the PersistentStateComponent class.

It has the following fields:

name (required) – specifies the name of the state (name of the root tag in XML).
storages – one or more of @Storage annotations to specify the storage locations. Optional for project-level values – a standard project file is used in this case.
reloadable (optional) – if set to false, a full project (or application) reload is required when the XML file is changed externally, and the state has changed.

The simplest ways of specifying the @Storage annotation are as follows:

@Storage(StoragePathMacros.WORKSPACE_FILE) – for values stored in the project workspace file (project-level components only).
@Storage("yourName.xml") – if a component is project-level, for .ipr-based projects, a standard project file is used automatically, and there is no need to specify anything.

The state is persisted in a separate file by specifying a different setting for the value parameter, which was the file parameter before 2016.x.

When planning your storage location, consider its intended purpose. A project-level custom file should be preferred for storing plugin settings. To store cached values, use @Storage(StoragePathMacros.CACHE_FILE). Refer to StoragePathMacros for commonly used macros.

The roamingType parameter of the @Storage annotation specifies the roaming type when the settings are shared:

RoamingType.DEFAULT – settings are shared
RoamingType.PER_OS – settings are shared per operating system
RoamingType.DISABLED – settings sharing is disabled

It is possible to share the persistent state of components between different IDE installations. This allows users to have the same settings on every development machine or to share their settings within a team.

Settings can be shared via the following functionalities:

Settings Sync plugin that allows synchronizing settings on JetBrains servers. Users can select the category of settings that are synchronized.
Settings Repository plugin that allows synchronizing settings in a Git repository created and configured by a user.
Export Settings feature that allows for the manual import and export of settings.

The decision about making a specific component's state shareable should be made carefully. Only the settings that aren't specific to a given machine should be shared, for example, paths to user-specific directories shouldn't be shared. If a component contains both shareable and non-shareable data, it should be split into two separate components.

Settings Sync Plugin

To include a plugin's component state in the Settings Sync plugin synchronization, the following requirements must be met:

The RoamingType is defined via the roamingType attribute of the @Storage annotation and is not equal to DISABLED.
The SettingsCategory is defined via the category attribute of the @State annotation and is not equal to OTHER.
There is no other PersistentStateComponent, which is stored in the same XML file and has a different RoamingType.

If the component state is OS-dependent, the roamingType of the @Storage annotation must be set to RoamingType.PER_OS.

Settings Repository Plugin and Export Settings Feature

Persistent components can be shared via the Settings Repository plugin and Export Settings feature, depending on the roamingType of the @Storage annotation. See the Defining the Storage Location for more details.

Customizing the XML Format of Persisted Values

If you want to use the default bean serialization but need to customize the storage format in XML (for example, for compatibility with previous versions of a plugin or externally defined XML formats), use the @Tag, @Attribute, @Property, @MapAnnotation, @XMap, and @XCollection annotations.

If the state to serialize doesn't map cleanly to a JavaBean, then org.jdom.Element can be used as the state class. In that case, use the getState() method to build an XML element with an arbitrary structure, which then is saved directly in the state XML file. In the loadState() method, deserialize the JDOM element tree using any custom logic. This is not recommended and should be avoided whenever possible.

To disable the expansion of path macros (PathMacro) in stored values, implement PathMacroFilter and register in com.intellij.pathMacroFilter extension point.

Migrating Persisted Values

If the underlying persistence model or storage format has changed, a ConverterProvider can provide ProjectConverter, whose getAdditionalAffectedFiles() method returns affected files to migrate and performs programmatic migration of stored values.

Persistent Component Lifecycle

The PersistentStateComponent.loadState() method is called after the component has been created (only if there is some non-default state persisted for the component), and after the XML file with the persisted state is changed externally (for example, if the project file was updated from the version control system). In the latter case, the component is responsible for updating the UI and other related components according to the changed state.

The PersistentStateComponent.getState() method is called every time the settings are saved (for example, on frame deactivation or when closing the IDE). If the state returned from getState() is equal to the default state (obtained by creating the state class with a default constructor), nothing is persisted in the XML. Otherwise, the returned state is serialized in XML and stored.

Using `PropertiesComponent` for Simple Non-Roamable Persistence

If the plugin needs to persist a few simple values, the easiest way to do so is to use the PropertiesComponent service. It can save both application-level values and project-level values in the workspace file. Roaming is disabled for PropertiesComponent, so use it only for temporary, non-roamable properties.

Use the PropertiesComponent.getInstance() method for storing application-level values and the PropertiesComponent.getInstance(Project) method for storing project-level values.

Since all plugins share the same namespace, it is highly recommended prefixing key names (for example, using plugin ID com.example.myCustomSetting).

Legacy API (`JDOMExternalizable`)

Older components use the JDOMExternalizable interface for persisting state. It uses the readExternal() method for reading the state from a JDOM element, and writeExternal() to write the state.

Implementations can manually store the state in attributes and sub-elements or use the DefaultJDOMExternalizer class to store the values of all public fields automatically.

Components save their state in the following files:

Project-level: project (.ipr) file. However, if the workspace option in the plugin.xml file is set to true, then the workspace (.iws) file is used instead.
Module-level: module (.iml) file.

Last modified: 17 September 2024