A plugin loader example program in kotlin-jvm
It should be pretty readable for Java coders.
It is part of another project that did not get finished.
It didn't finish the other project because, instead of doing this, I should have used OSGi, which I didn't know about until after I had started. That way I wouldn't have spent a few weeks doing this instead.
It's JUST the plugin loader, and it has a jar for the entrypoint, a jar for the api that can be imported by the plugin, and a jar for program with the plugin loader itself.
It also has a couple plugins for testing, one of which is minesweeper but loaded as a plugin from this repo
gradle is used for build, so just gradle build shadowJar
Default plugin directory when you run it assumes you are at project root but you can specify.
java -jar ExampleOut/entryPoint.jar 1 <optional path to plugins>
Main is in entryPoint:
Main.kt sets up the shared parent which has the api in its classpath.
It is parent for both the program's loader and the plugin loaders.
Main.kt then launches the program with the program loader.
Minimal API in exampleAPI:
The only api functions of note are a shutdown hook, and the interface to implement to make a plugin.
The hook from the user is passed to PluginManager in a "plugistration" implementation
// registering a plugin
package examplepluginloader.api.plugin;
public class PluginLoading implements MyPlugin {
public void launchPlugin(MyAPI api){
// do plugin stuff with the api
api.plugin().registerShutdownSequence(new PluginUnloadHandler(){
public void pluginUnloaded(){
// cleanup code if needed
}
});
}
}- most of the api used above
package examplepluginloader.api
import examplepluginloader.api.plugin.ManagePlugins
public interface MyAPI {
//this would normally have a lot more things in it.
// the api you want to expose to plugins will go here
// but right now it only has plugin lifecycle stuff
fun plugin(): ManagePlugins
}package examplepluginloader.api
import examplepluginloader.api.MyAPI
public interface MyPlugin {
fun launchPlugin(api: MyAPI)
}package examplepluginloader.api.plugin;
public interface ManagePlugins{
fun pluginLocation(): URL?
fun unloadPlugin()
fun registerShutdownSequence(unldHndlr: PluginUnloadHandler): Plugistration
}Main logic in examplepluginloader:
PluginLoader.kt is the loader for the plugins, 1 new one is created for each one.
PluginManager manages the instances and has the functions for opening and closing
MyProgram calls functions from PluginManager, and prints output.
side note:
JByteCodeURLINFO.kt just gets class names in a jar. Top 45 lines of that file should be all you need for debug.
As far as PluginManager is concerned it just finds class names of plugins.
It does not hold any references to the active plugin classes themselves and all input streams are closed.
The parts of note are at the following locations: