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Development Documentation 2.20.0

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Hop File Types

A Hop file type plugin teaches the Hop GUI how to recognize, display, and open specific file extensions (such as .hpl, .hwf, .json, .csv, .sql, or .parquet). File types define the icon used in the Explorer perspective, the file filter masks in file-open dialogs, and the editor opened when double-clicking a file.

Implementing a File Type

Annotate your class with @HopFileTypePlugin and extend HopFileTypeBase:

java
import java.util.Properties;
import org.apache.hop.core.exception.HopException;
import org.apache.hop.core.variables.IVariables;
import org.apache.hop.ui.hopgui.HopGui;
import org.apache.hop.ui.hopgui.file.HopFileTypeBase;
import org.apache.hop.ui.hopgui.file.HopFileTypePlugin;
import org.apache.hop.ui.hopgui.file.IHopFileType;
import org.apache.hop.ui.hopgui.file.IHopFileTypeHandler;
import org.apache.hop.ui.hopgui.file.empty.EmptyHopFileTypeHandler;

@HopFileTypePlugin(
    id = "CustomMarkdownFileType",
    name = "Markdown File",
    description = "Documentation and markdown files",
    image = "markdown.svg"
)
public class MarkdownFileType extends HopFileTypeBase implements IHopFileType {

  public static final String[] EXTENSIONS = new String[] {"*.md", "*.markdown"};

  @Override
  public String getName() {
    return "Markdown";
  }

  @Override
  public String[] getFilterExtensions() {
    return EXTENSIONS;
  }

  @Override
  public String[] getFilterNames() {
    return new String[] {"Markdown Files (*.md, *.markdown)"};
  }

  @Override
  public String getDefaultFileExtension() {
    return "md";
  }

  @Override
  public Properties getCapabilities() {
    Properties capabilities = new Properties();
    capabilities.setProperty(IHopFileType.CAPABILITY_SAVE, "true");
    capabilities.setProperty(IHopFileType.CAPABILITY_SAVE_AS, "true");
    capabilities.setProperty(IHopFileType.CAPABILITY_CLOSE, "true");
    return capabilities;
  }

  @Override
  public IHopFileTypeHandler openFile(HopGui hopGui, String filename, IVariables variables)
      throws HopException {
    // Create the handler for this file and open it in the perspective that edits the type.
    return new EmptyHopFileTypeHandler();
  }
}

HopFileTypeBase.hasCapability(String) reads that map. Capability names are the CAPABILITY_* constants on IHopFileType. Explorer file types build the same map with FileTypeCapabilities.getCapabilities(String…​) in org.apache.hop.ui.hopgui.perspective.explorer.file.capabilities.

Key Methods

  • getFilterExtensions(): String array of wildcard patterns (e.g., {"*.parquet"}).

  • openFile(HopGui, String, IVariables): Instantiates or activates the appropriate editor or perspective tab.

  • hasCapability(String): Informs the GUI whether the file supports an operation such as save, close, or creation.

  • getContextHandlers(): Provides custom actions in right-click context menus in the file explorer.

Concrete Codebase Examples

  • ui/src/main/java/org/apache/hop/ui/hopgui/file/pipeline/HopPipelineFileType.java: The core file type handling .hpl pipeline files.

  • ui/src/main/java/org/apache/hop/ui/hopgui/perspective/explorer/file/types/text/BaseTextExplorerFileType.java: Plain text file handler in the Explorer perspective.

  • ui/src/main/java/org/apache/hop/ui/hopgui/perspective/explorer/file/types/log/LogExplorerFileType.java: Log viewer file type.

See also