5.1. Introduction to the plugin mechanism

Plugins are extensions that add additional functionality to the Importer/Exporter. They are self-contained in that one plugin cannot extend the functionality of another plugin. Therefore, plugins can be added separately to the Importer/Exporter without interdependencies.

A plugin may extend the GUI of the Importer/Exporter by providing its own user dialog that will be rendered in a separate tab on the operations window. In addition, a plugin may add new entries to the main menu bar and the preferences dialog. To restore plugin-specific settings at program startup, a plugin can choose to serialize the settings to the main config file or a plugin-specific config file. Besides GUI extensions, plugins can also provide functionality that is hooked into the main operations of the Importer/Exporter, for instance, to postprocess exported top-level features. And they can add their own commands to the CLI of the Importer/Exporter to run the plugin from the command line.

Plugin installation is simple. Just get the plugin from your vendor and put all plugin files into the plugins subfolder of the Importer/Exporter installation directory. To keep multiple plugins independent from each other, it is recommended to create a separate subfolder below plugins for each plugin. When running the Importer/Exporter, the installed plugins are automatically detected and loaded with the application. Uninstalling a plugin just requires to delete the folder containing all the plugin files from the plugins subfolder. Note that changes to the plugins subfolder require a restart of the Importer/Exporter to become effective.

Installed plugins can be enabled or disabled at runtime both using the graphical user interface of the Importer/Exporter (see Section 4.7.1) and on the command line (see Section 4.9).

The Importer/Exporter is shipped with two free and open-source plugins that can be installed during the setup process (see Section 1.2). The Spreadsheet Generator Plugin allows for exporting attributes of city objects as spreadsheets with user-defined formatting, either to a CSV or a Microsoft Excel file (see Section 5.2). The ADE Manager Plugin automatically transforms CityGML ADEs to relational schemas extending the 3DCityDB schema and un-/registers such ADE schemas with existing 3DCityDB instances.

You can also develop your own plugins. For this purpose, the Importer/Exporter comes with a Plugin API that is available from the JAR file impexp-core-{version}.jar. Simply put this JAR file on your classpath to start plugin development. The source codes of the Spreadsheet Generator Plugin and ADE Manager Plugin can be used as templates for your own developments.