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1. What You Will Learn

After finishing this tutorial you will be able to write your own PAK App including a JarCommandPool which is capable of running workflows.

This guide will build up on this guide: how to build and run commands.

2. Prerequisites

To complete this guide you need:

3. Setup

Now you have to set up our project. We will provide guides for a setup with gradle and with maven.

3.1. Setup with Gradle

First open your selected IDE and create a new Gradle project with the following configuration:

Figure 1. Configuration for a Gradle project

Select a name for your project:

Figure 2. Set project name

Inside the ‚build.gradle‘ the following build script is required:

Figure 3. build gradle file
plugins {
    id 'java-library'

ext {
    // dependency version
    pakVersion = '1.5.14'

repositories {
    maven {
        name = 'pak-explorer-maven'
        url 'https://pak.asap.de/nexus/repository/pak-explorer-maven/'

dependencies {
    implementation "de.asap.pak.core:pak-engine:${pakVersion}"
    implementation "de.asap.pak.core:pak-simple:${pakVersion}"
    implementation "de.asap.pak.bpmn-model:bpmn-interpreter:${pakVersion}"
    implementation "de.asap.pak.extra:pak-jarpool:${pakVersion}"

    runtimeOnly "de.asap.pak.core:pak-commandjson:${pakVersion}"
    runtimeOnly "de.asap.pak.core:pak-default-datatransformer:${pakVersion}"
    runtimeOnly "de.asap.pak.jlcint:jlcint-interpreter:${pakVersion}"
    runtimeOnly "de.asap.pak.jlcint:jlcint-pakbridge:${pakVersion}"

    // Optional but useful for logging the work
    implementation 'org.slf4j:slf4j-api:1.7.25'
    implementation 'ch.qos.logback:logback-classic:1.4.0'

3.2. Setup with Maven

First open your selected IDE and create a new Maven project with the following configuration:

Figure 4. Configuration for a Maven Project

Select a name for your project:

Figure 5. Set project name

The ‚pom.xml‘ requires the following xml:

Pom File
Figure 6. pom file
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">









4. Implementation

For our example app we need to implement a few things:

  • an Engine that runs the workflow.

  • an EngineObserver which logs the events which are fired by the Engine.

  • an AppClass which starts the whole application.

4.1. The Engine Observer

At first, we will implement an EngineObserver that logs events from our Engine.

import de.asap.pak.core.engine.spi.interceptors.EngineEvent;
import de.asap.pak.core.engine.spi.interceptors.IEngineListenerEvent;
import de.asap.pak.core.engine.spi.interceptors.IEngineObserver;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

 * Example Observer to show the registration of an engine observer
public class EngineObserver implements IEngineObserver {

	// Create a logger for this class
	private static final Logger LOG = LoggerFactory.getLogger(EngineObserver.class);

	public void observe(IEngineListenerEvent event){
		EngineEvent engineEvent = event.getEvent();

		switch (engineEvent) {

	private void handleWorkflowStarted(){
		LOG.info("The workflow has been started!");

	private void handleWorkflowFinished(){
		LOG.info("The workflow has finished!");
If you want to know more about Engine-Observers & Callbacks click here

4.2. The Engine

Now we are going to implement the engine, and therefore we need some components.

import de.asap.pak.core.commandpool.spi.ICommandPool;
import de.asap.pak.core.context.api.IContext;
import de.asap.pak.core.context.impl.ContextBuilder;
import de.asap.pak.core.context.services.spi.IPersistenceService;
import de.asap.pak.core.engine.api.IEngine;
import de.asap.pak.core.engine.impl.EngineBuilder;
import de.asap.pak.core.engine.spi.mapping.IMappingService;
import de.asap.pak.core.model.api.IModel;
import de.asap.pak.core.simple.context.SimplePersistenceService;
import de.asap.pak.core.simple.context.SimpleServiceProviderFactory;
import de.asap.pak.extra.jarpool.JarCommandPool;
import de.asap.pak.modelinterpreter.bpmn.BPMNModelInterpreter;
import de.asap.pak.modelinterpreter.bpmn.mapping.MappingService;
import de.asap.pak.modelinterpreter.bpmn.model.validator.ModelException;

import java.io.InputStream;

* Class for creating an engine
public final class EngineCreator {

	private EngineCreator() {

	 * This method configures an engine using the PAK Engine builder by using default implementations
	 * @param is Input-Stream object, which refers to a BPMN-File
	public static IEngine createEngine(final InputStream is) throws ModelException {
		//in our case we want to execute a Bpmn therefore we create the interpreter to parse and create a model
		final BPMNModelInterpreter interpreter = BPMNModelInterpreter.withInputStreamSource(is);
		// Creating an instance of Model which is going to be executed
		final IModel model = interpreter.parseToModel(); (1)
		// In this example we use the JarCommandPool for providing the commands  to the app
		final ICommandPool pool = new JarCommandPool(); (2)
		// Each Engine needs a "Context" which provides all needed data and services to the engine
		final ContextBuilder cb = new ContextBuilder(); (3)
		// In order to create a context, a serviceprovider factory needs to be passed. The factory will create a ServiceProvider which will hold all important services for the engine
		final SimpleServiceProviderFactory factory = new SimpleServiceProviderFactory(); (4)
		// The persistence service will save all data which is created when executing the workflow model
		factory.addService(IPersistenceService.class,new SimplePersistenceService()); (5)
		factory.addService(IMappingService.class, new MappingService());
		// Create the Context instance
		final IContext context = cb.build(); (3)
		// Now we got everything we need to build a engine
		final IEngine engine = new EngineBuilder().setCommandPool(pool).setContext(context).setModel(model).build(); (6)

		//we also register our EngineObserver we have written before
		final EngineObserver engineObserver = new EngineObserver();
		return engine;

In the code above we see some PAK core components, which we want to explain a little more


(1) Is the model that is going to be executed by the engine.


(2) A CommandPool provides in general a collection of commands and their needed services. In the specific case of an JarCommandPool the commands are directly provided by one or multiple jars. For a real app we would suggest the MavenCommandPool


(3) The context contains all information and services for the engine


(4) The ServiceProvider provides all kind of services that are needed for executing the model


(5) A PersistenceService is responsible for persisting and providing all data created/read by the commands.


(6) Is the central class which controls the complete execution of the given workflow model

Click the links for more in-depth information about each topic.

4.3. The App class

The App class will create the engine and execute the workflow.

import de.asap.pak.core.engine.api.IEngine;
import de.asap.pak.core.engine.api.WorkflowException;
import de.asap.pak.modelinterpreter.bpmn.model.validator.ModelException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.io.InputStream;

public class App {
	//Create a logger for this class
	private static final Logger LOG = LoggerFactory.getLogger(App.class);

	public void start() {

		IEngine engine = null;

		try (final InputStream inputStream = getClass().getClassLoader().getResourceAsStream("Hello_World.bpmn")) {
			engine = EngineCreator.createEngine(inputStream);
		} catch (ModelException | IOException e) {
			LOG.error("Unable to parse the BPMN-File to a model", e);

		try {
			//Start the engine
		} catch (WorkflowException e) {
			LOG.error("Unable to run the workflow", e);

	public static void main(String[] args) {
		//run the start method of the app
		new App().start();

5. Run the App

The app is basically now ready, but before executing the code we need to provide the bpmn and commands properly.

5.1. Provide the BPMN

Just place the BPMN (from the ‚Create your First Command‚ guide) to the resource folder of your project or download it from here.


5.2. Provide the Commands

In order for the commands (from the ‚Create your First Command‚ guide) to be found by the Commandpool we need to add the dependency to our project

Make sure the example command is already published to maven local or a remote maven repository. Click here if you need more information for publishing commands locally.
for gradle
//this is the dependency to the example-commands jar which was published locally to mavenLocal
runtimeOnly "org.example:example-commands:1.0.0"
for maven

5.3. Run the App

The App is now ready to run!

To do so select the created App class → Click the green play icon in the gutter and select Run ‚App.main()‘

Figure 7. Run the App first time

And you can see the expected output from the Command in the logs.

Successful Run

In the logs our implemented simple EngineObserver provides additional information.

Figure 8. Ran engine logs