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Chapter 21. Domain-specific Processes

21.1. Introduction
21.2. Overview
21.2.1. Work Item Definitions
21.2.2. Work Item Handlers
21.3. Example: Notifications
21.3.1. The Notification Work Item Definition
21.3.2. The NotificationWorkItemHandler
21.4. Service Repository
21.4.1. Public jBPM service repository
21.4.2. Setting up your own service repository
21.4.3. Programatically interacting with the service repository
21.4.4. Defining extended service configuration with JSON
21.4.5. Installing services from the service repositoryy

jBPM provides the ability to create and use domain-specific task nodes in your business processes. This simplifies development when you're creating business processes that contain tasks dealing with other technical systems.

When using jBPM, we call these domain-specific task nodes "custom work items" or (custom) "service nodes". There are two separate aspects to creating and using custom work items:

With regards to a BPMN2 process, custom work items are certain types of <task> nodes. In most cases, custom work items are <task> nodes in a BPMN2 process definition, although they can also be used with certain other task type nodes such as, among others, <serviceTask> or <sendTask> nodes.

Users can thus easily define their own set of domain-specific service nodes and integrate them with the process language. For example, the next figure shows an example of a healthcare-related BPMN2 process. The process includes domain-specific service nodes for measuring blood pressure, prescribing medication, notifying care providers and following-up on the patient.

Before moving on to an example, this section explains what custom work items and custom work item handlers are.

A work item handler is a Java class used to execute (or abort) work items. That also means that the class implements the org.kie.runtime.instance.WorkItemHandler interface. While jBPM provides some custom WorkItemHandler instances (listed below), a Java developer with a minimal knowledge of jBPM can easily create a new work item handler class with its own custom business logic.

Among others, jBPM offers the following WorkItemHandler implementations:

There are a many more WorkItemHandler implementations present in the jbpm-workitems module. If you're looking for specific integration logic with Twitter, for example, we recommend you take a look at the classes made available there.

In general, a WorkItemHandler's .executeWorkItem(...) and .abortWorkItem(...) methods will do the following:

WorkItemManager.completeWorkItem(long workItemId, Map<String, Object> results)
WorkItemManager.abortWorkItem(long workItemId)

In order to make sure that your custom work item handler is used for a particular process instance, it's necessary to register the work item handler before starting the process. This makes the engine aware of your WorkItemHandler so that the engine can use it for the proper node. For example:

    new NotificationWorkItemHandler());

The ksession variable above is a StatefulKnowledgeSession (and also a KieSession) instance. The example code above comes from the example that we will go through in the next session.

Work item handler life cycle management

Work item handler is registered on kie session and then can be used whenever process engine encounters a node that should be handled by that handler. Depending on the implementation of the handler (e.g. some handler might keep state or depend on some resources such as data base connection) there might be a need to maintain life cycle of the handler. To ease the way of doing that jBPM comes with two additional interfaces that handler might implement:

Closeable interface is handled for all use cases, while Cacheable is available only when RuntimeManager is used. RuntimeManager provides caching capabilities via its CacheManager (available via InternalRuntimeManager in case self removal is required).

Let's start by showing you how to include a simple work item for sending notifications. A work item is defined by a unique name and includes additional parameters that describe the work in more detail. Work items can also return information after they have been executed, specified as results.

Our notification work item could be defined using a work definition with four parameters and no results. For example:

We've created our work item definition and configured it, so now we can start using it in our processes. The process editor contains a separate section in the palette where the different service nodes that have been defined for the project appear.

Using drag and drop, a notification node can be created inside your process. The properties can be filled in using the properties view.

Besides any custom properties, the following three properties are available for all work items:

Here is an example that creates a domain specific node to execute Java, asking for the class and method parameters. It includes a custom java.gif icon and consists of the following files and resulting screenshot:

import org.drools.core.process.core.datatype.impl.type.StringDataType;
  // the Java Node work item located in:
  // project/src/main/resources/META-INF/JavaNodeDefinition.wid
    "name" : "JavaNode",
    "parameters" : [
      "class" : new StringDataType(),
      "method" : new StringDataType(),
    "displayName" : "Java Node",
    "icon" : "icons/java.gif"

// located in: project/src/main/resources/META-INF/drools.rulebase.conf
drools.workDefinitions = JavaNodeDefinition.wid WorkDefinitions.conf

// icon for java.gif located in:
// project/src/main/resources/icons/java.gif

Once we've created our Notification work item definition (see the sections above), we can then create a custom implementation of a work item handler that will contain the logic to send the notification.

In order to execute our Notification work items, we first create a NotificationWorkItemHandler that implements the WorkItemHandler interface:

This WorkItemHandler sends a notification as an email and then notifies the WorkItemManager that the work item has been completed.

Note that not all work items can be completed directly. In cases where executing a work item takes some time, execution can continue asynchronously and the work item manager can be notified later.

In these situations, it might also be possible that a work item is aborted before it has been completed. The WorkItemHandler.abortWorkItem(...) method can be used to specify how to abort such work items.

WorkItemHandler instances need to be registered with the WorkItemManager in order to be used. In this case, we need to register an instance of our NotificationWorkItemHandler in order to use it with our process containing a Notification work item. We can do that like this:

StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();
  "Notification",                                          (1)
  new NotificationWorkItemHandler()                        (2)


This is the drools name of the <task> (or other task type) node. See below for an example.


This is the instance of our custom work item handler instance!

If we were to look at the BPMN2 syntax for our process with the Notification process, we would see something like the following example. Note the use of the tns:taskName attribute in the <task> node. This is necessary for the WorkItemManager to be able to see which WorkItemHandler instance should be used with which task or work item.

<?xml version="1.0" encoding="UTF-8"?> 
<definitions id="Definition"
             xs:schemaLocation="http://www.omg.org/spec/BPMN/20100524/MODEL BPMN20.xsd"


  <process isExecutable="true" id="myCustomProcess" name="Domain-Specific Process" >


    <task id="_5" name="Notification Task" tns:taskName="Notification" >


A lot of these domain-specific services are generic, and can be reused by a lot of different users. Think for example about integration with Twitter, doing file system operations or sending email. Once such a domain-specific service has been created, you might want to make it available to other users so they can easily import and start using it.

A service repository allows you to import services by browsing the repository looking for services you might need and importing these services into your workspace. These will then automatically be added to your palette and you can start using them in your processes. You can also import additional artefacts like for example an icon, any dependencies you might need, a default handler that will be used to execute the service (although you're always free to override the default, for example for testing), etc.

To browse the repository, open the wizard to import services, point it to the right location (this could be to a directory in your file system but also a public or private URL) and select the services you would like to import. For example, in Eclipse, right-click your project that contains your processes and select "Configure ... -> Import jBPM services ...". This will open up a repository browser. In the URL field, fill in the URL of your repository (see below for the URL of the public jBPM repository that hosts some common service implementations out-of-the-box), or use the "..." button to browse to a folder on your file system. Click the Get button to retrieve the contents of that repository.

Select the service you would like to import and then click the Import button. Note that the Eclipse wizard allows you to define whether you would like to automatically configure the service (so it shows up in the palette of your processes), whether you would also like to download any dependencies that might be needed for executing the service and/or whether you would like to automatically register the default handler, so make sure to mark the right checkboxes before importing your service (if you are unsure what to do, leaving all check boxes marked is probably best).

After importing your service, (re)open your process diagram and the new service should show up in your palette and you can start using it in your process. Note that most services also include documentation on how to use them (e.g. what the different input and output parameters are) when you select them browsing the service repository.

Click on the image below to see a screencast where we import the Twitter service in a new jBPM project and create a simple process with it that sends an actual tweet. Note that you need the necessary Twitter keys and secrets to be able to programmatically send tweets to your Twitter account. How to create these is explained here, but once you have these, you can just drop them in your project using a simple configuration file.

Figure 21.1. 

We are building a public service repository that contains predefined services that people can use out-of-the-box if they want to:


This repository contains some integrations for common services like Twitter integration or file system operations that you can import. Simply point the import wizard to this URL to start browsing the repository.

If you have an implementation of a common service that you would like to contribute to the community, do not hesitate to contact someone from the development team. We are always looking for contributions to extend our repository.

You can set up your own service repository and add your own services by creating a configuration file that contains the necessary information (this is an extended version of the normal work definition configuration file as described earlier in this chapter) and putting the necessary files (like an icon, dependencies, documentation, etc.) in the right folders.

The extended configuration file contains the normal properties (like name, parameters, results and icon), with some additional ones. For example, the following extended configuration file describes the Twitter integration service (as shown in the screencast above):

import org.drools.core.process.core.datatype.impl.type.StringDataType;
    "name" : "Twitter",
    "description" : "Send a Twitter message",
    "parameters" : [
      "Message" : new StringDataType()
    "displayName" : "Twitter",
    "eclipse:customEditor" : "org.drools.eclipse.flow.common.editor.editpart.work.SampleCustomEditor",
    "icon" : "twitter.gif",
    "category" : "Communication",
    "defaultHandler" : "org.jbpm.process.workitem.twitter.TwitterHandler",
    "documentation" : "index.html",
    "dependencies" : [

The root of your repository should also contain an index.conf file that references all the folders that should be processed when searching for services on the repository. Each of those folders should then contain:

You can create your own hierarchical structure, because if one of those folders also contains an index.conf file, that will be used to scan additional sub-folders. Note that the hierarchical structure of the repository is not shown when browsing the repository using the import wizard, as the category property in the configuration file is used for that.

The Workbench provides two ways of installing services from the user defined service repositories: