Dynamic plugins loading using JCL (https://github.com/kamranzafar/JCL/) This is an example of a plugin that can be used with the babysitter server (https://github.com/massenz/babysitter)

SamplePlugin.java

package com.rivermeadow.plugins.simple;

import com.rivermeadow.babysitter.alerts.AlertPlugin;
import com.rivermeadow.babysitter.alerts.Context;
import com.rivermeadow.babysitter.alerts.Pager;
import com.rivermeadow.babysitter.model.Server;

/**
 * Simplest example of a ``babysitter`` plugin, does nothing but demonstrate how to create a pluggable component.
 *
 * @author marco
 */
public class SamplePlugin implements Pager, AlertPlugin {

    private static final String TEST = "plugins.simple.test";
    Context ctx;

    @Override
    public void startup(Context ctx) {
        this.ctx = ctx;
        ctx.setNamedProperty(TEST, "value-99");
    }

    @Override
    public Pager activate() {
        return this;
    }

    @Override
    public void deactivate() {
    }

    @Override
    public void shutdown() {
    }

    @Override
    public String getName() {
        return getClass().getCanonicalName();
    }

    @Override
    public String getDescription() {
        return "This is a Sample plugin, to test JCL";
    }

    @Override
    public String getPagerClassName() {
        return getClass().getCanonicalName();
    }

    @Override
    public void page(Server server) {
        String value = (String) ctx.getNamedProperty(TEST);
        System.out.println("The value is: " + value);
        System.out.println("This is an alert for the Sample plugin: " + server.getDescription());
    }
}

ServerLoader.java

    // Obviously this would be POSTed as a file upload
    jarClassLoader.add("/tmp/jcl-test.jar");

    //Create object of loaded class
    Object obj = factory.create(jarClassLoader, fqn);
    AlertPlugin plugin = JclUtils.cast(obj, AlertPlugin.class);
    logger.info("Loaded valid AlertPlugin: " + plugin.getName() + " :: " + plugin.getDescription());
    
    // ctx is an instance of the Context class and provides a generic plugin context
    plugin.startup(ctx);
    Pager pager = JclUtils.cast(plugin.activate(), Pager.class);
    logger.info("Plugin activated, obtained Pager: " + pager.getClass().getName());
    
    // Once we register the Pager with the AlertManager, it can start receiving actual pages
    Server fakeServer = new Server(new ServerAddress("test", "10.10.0.100"), 80, 30);
    fakeServer.setDescription("This is a fake server");
    pager.page(fakeServer);
    
    // the output from the SamplePlugin will be:
    The value is: value-99
    This is an alert for the Sample plugin: This is a fake server