strolch-website/content/documentation/observers.md

title	weight
Observers	110

Observers

All changes done in a Strolch transaction are recorded and then propagated to any registered observers.

The observer feature is opt-in and is configured for each realm. In the StrolchConfiguration.xml file enable observers by adding the enableObserverUpdates property per realm:

<StrolchConfiguration>
  <env id="dev">
    ...
    <Component>
      <name>RealmHandler</name>
      <api>li.strolch.agent.api.RealmHandler</api>
      <impl>li.strolch.agent.impl.DefaultRealmHandler</impl>
      <depends>PrivilegeHandler</depends>
      <Properties>
        <realms>defaultRealm, otherRealm</realms>
        <enableObserverUpdates>true</enableObserverUpdates>
        <dataStoreMode>TRANSIENT</dataStoreMode>
        <dataStoreFile>StrolchModel.xml</dataStoreFile>
        <enableObserverUpdates.otherRealm>true</enableObserverUpdates.otherRealm>
        <dataStoreMode.otherRealm>TRANSIENT</dataStoreMode.otherRealm>
        <dataStoreFile.otherRealm>StrolchModel.xml</dataStoreFile.otherRealm>
      </Properties>
    </Component>
  </env>
  ...
</StrolchConfiguration>

Registering for updates is done by registering an Observer on the ObserverHandler of the realm itself:

ObserverHandler observerHandler = container.getRealm(StrolchConstants.DEFAULT_REALM).getObserverHandler();
observerHandler.registerObserver(Tags.RESOURCE, new Observer() {

  @Override
  public void update(String key, List<StrolchRootElement> elements) {
    logger.info(elements.size() + " resources were updated!");
  }

  @Override
  public void remove(String key, List<StrolchRootElement> elements) {
    logger.info(elements.size() + " resources were removed!");
  }

  @Override
  public void add(String key, List<StrolchRootElement> elements) {
    logger.info(elements.size() + " resources were added!");
  }
});