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Development Documentation 2.20.0

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Metadata Element Plugins

Metadata element plugins add new types of reusable configurations to Apache Hop: database connections, pipeline run configurations, execution information locations, and custom API connections. These objects are edited in the Hop GUI Metadata perspective and stored as JSON files under the project’s metadata/ directory.

1. The Metadata Class

Create a POJO extending HopMetadataBase and implementing IHopMetadata, annotated with @HopMetadata:

java
import org.apache.hop.core.gui.plugin.GuiPlugin;
import org.apache.hop.metadata.api.HopMetadata;
import org.apache.hop.metadata.api.HopMetadataBase;
import org.apache.hop.metadata.api.HopMetadataProperty;
import org.apache.hop.metadata.api.IHopMetadata;
import lombok.Getter;
import lombok.Setter;

@HopMetadata(
    key = "webhook-notification",             // Storage folder name (kebab-case)
    legacyKeys = {"WebhookNotification"},     // Backward compatibility
    name = "Webhook Notification",
    description = "Defines a webhook endpoint for workflow notifications",
    image = "webhook.svg",
    category = "Alerts"
)
@GuiPlugin
@Getter
@Setter
public class WebhookNotification extends HopMetadataBase implements IHopMetadata {

  public static final String GUI_PLUGIN_ELEMENT_PARENT_ID = "WebhookNotification-Parent";

  @HopMetadataProperty
  private String url;

  @HopMetadataProperty(password = true)
  private String secretToken;

  @HopMetadataProperty
  private int retries = 3;

  public WebhookNotification() {
    super();
  }

  public WebhookNotification(String name, String url, String secretToken) {
    this.name = name;
    this.url = url;
    this.secretToken = secretToken;
  }
}

Naming Rules for @HopMetadata

  • key: Must be lower-case kebab-case (webhook-notification). This forms the folder path metadata/webhook-notification/<name>.json.

  • legacyKeys: If you ever rename a key, include the previous key in legacyKeys so older projects continue loading their configurations seamlessly.

2. The GUI Metadata Editor (*Editor)

A metadata editor extends MetadataEditor. The editor creates the name field, and the other fields come from @GuiWidgetElement on the metadata class. Pass that name control into createCompositeWidgets. The worked example is Annotation derived widgets, under "Metadata editors".

3. Selecting Metadata in Transform and Action Dialogs

To let users select a metadata element in another dialog:

  • Use MetaSelectionLine<T> directly in SWT:

    java
    MetaSelectionLine<WebhookNotification> wWebhook = new MetaSelectionLine<>(
    variables, metadataProvider, WebhookNotification.class,
    shell, SWT.NONE, "Webhook", "Select the webhook configuration"
);
wWebhook.fillItems();

  • Or annotate the field with @GuiWidgetElement(type = GuiElementType.METADATA). The layout is Annotation derived widgets.

Concrete Codebase Examples

  • engine/src/main/java/org/apache/hop/partition/PartitionSchema.java and ui/src/main/java/org/apache/hop/ui/partition/PartitionSchemaEditor.java: Standard in-tree metadata object with editor.

  • plugins/tech/sftp/src/main/java/org/apache/hop/vfs/sftp/metadata/SftpConnection.java: Connection metadata element.

See also