<dependency>
    <groupId>org.pf4j</groupId>
    <artifactId>pf4j</artifactId>
    <version>3.0.1</version>
</dependency>

package com.et.pf4j;

import org.pf4j.ExtensionPoint;

public interface Greeting extends ExtensionPoint {

    String getGreeting();

}

/*
 * Copyright (C) 2012-present the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.pf4j.demo.welcome;

import com.et.pf4j.Greeting;
import org.apache.commons.lang.StringUtils;

import org.pf4j.Extension;
import org.pf4j.Plugin;
import org.pf4j.PluginWrapper;
import org.pf4j.RuntimeMode;

/**
 * @author Decebal Suiu
 */
public class WelcomePlugin extends Plugin {

    public WelcomePlugin(PluginWrapper wrapper) {
        super(wrapper);
    }

    @Override
    public void start() {
        System.out.println("WelcomePlugin.start()");
        // for testing the development mode
        if (RuntimeMode.DEVELOPMENT.equals(wrapper.getRuntimeMode())) {
            System.out.println(StringUtils.upperCase("WelcomePlugin"));
        }
    }

    @Override
    public void stop() {
        System.out.println("WelcomePlugin.stop()");
    }

    @Extension
    public static class WelcomeGreeting implements Greeting {

        @Override
        public String getGreeting() {
            return "Welcome ,my name is pf4j-plugin-01";
        }

    }

}

package com.et.pf4j;

import org.pf4j.JarPluginManager;
import org.pf4j.PluginManager;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import java.nio.file.Paths;
import java.util.List;

@SpringBootApplication
public class DemoApplication {

/* public static void main(String[] args) {
      SpringApplication.run(DemoApplication.class, args);
   }*/
   public static void main(String[] args) {


      // create the plugin manager
      PluginManager pluginManager = new JarPluginManager(); // or "new ZipPluginManager() / new DefaultPluginManager()"

      // start and load all plugins of application
      //pluginManager.loadPlugins();

      pluginManager.loadPlugin(Paths.get("D:\\IdeaProjects\\ETFramework\\pf4j\\pf4j-plugin-01\\target\\pf4j-plugin-01-1.0-SNAPSHOT.jar"));
      pluginManager.startPlugins();
      /*
        // retrieves manually the extensions for the Greeting.class extension point
        List<Greeting> greetings = pluginManager.getExtensions(Greeting.class);
        System.out.println("greetings.size() = " + greetings.size());
        */
      // retrieve all extensions for "Greeting" extension point
      List<Greeting> greetings = pluginManager.getExtensions(Greeting.class);
      for (Greeting greeting : greetings) {
         System.out.println(">>> " + greeting.getGreeting());
      }

      // stop and unload all plugins
      pluginManager.stopPlugins();
      //pluginManager.unloadPlugins();


   }
}