Loading plugins

Plugin main class should contain the following methods:

public static void loadPlugins() {}
public static void unloadPlugins() {}

The loadPlugins() method is executed on application startup before any GUI initialization. The plugin initialization class should analyze OmegaT version and register classes for filters:

Core.registerFilterClass(MyFilter.class);

Also, the initialization class can register its own event handlers, for example, for GUI initialization on application startup:

CoreEvents.registerApplicationEventListener(...);

The loadPlugins() method should check OmegaT version, or existing interface, or other things required for plugin execution. If the plugin cannot be loaded, it can send some error message which will be displayed to the user after GUI initialization:

Core.pluginLoadingError(“Some message”);

Since the plugin is likely to use some OmegaT classes, which can be changed in a future OmegaT version, we recommend separating plugin initialization class and plugin implementation class.

Also, it will be better to do not use any other classes (except Core and CoreEvents) in import declarations of the plugin initialization class, so that it can catch loading errors and send a clear error message.

You can check if required classes and methods exist, or check the OmegaT version number.

Below, you see an example that checks for existence of VersionChecker class (doesn't exist in OmegaT3) and next checks the version number.

    public static void loadPlugins() {
        try {
            //analyze OmegaT version:
            String requiredVersion = "5.4.0";
            String requiredUpdate = "0";
            try {
                Class<?> clazz = Class.forName("org.omegat.util.VersionChecker");
                Method compareVersions = clazz.getMethod("compareVersions", String.class, String.class, String.class, String.class);
                if ((int)compareVersions.invoke(clazz, OStrings.VERSION, OStrings.UPDATE, requiredVersion, requiredUpdate) < 0) {
                    Core.pluginLoadingError("Plugin … cannot be loaded because OmegaT Version "+OStrings.VERSION+" is lower than required version "+requiredVersion);
                    return;
                }
            } catch (ClassNotFoundException | NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {
                Core.pluginLoadingError("Plugin … cannot be loaded because this OmegaT version is not supported");
                return;
            }
            // … register classes and events …
        } catch(Throwable ex) {
            Core.pluginLoadingError(“Plugin … cannot be loaded because this version of OmegaT is not supported”);
        }
    }

The loadPlugins() method shouldn't execute any long operations. The unloadPlugins() method executes on application shutdown. Usually, it should be just an empty method, but it can be used to free some resources.