9.8.1. Task event listener

Task service supports task listeners to be invoked upon various life cycle events happening on given task instance. In majority of cases task event listeners are used to intercept certain operation to perform additional logic - like storing task information in separate tables for business activity monitoring needs.

Task event listeners are pluggable and users can provide their own implementation of org.kie.api.task.TaskLifeCycleEventListener interface. There are beforeTask* and afterTask* methods that are invoked upon given event occured on a task instance.

TaskEvent (org.kie.api.task.TaskEvent) is the only argument available to the listener that provides access to:

Task instance that the event correspond to

TaskContext that provides access to services for further processing needs such as TaskPersistenceContext

In many cases implementors of task event listener need to have access to task variables (either input or output or both) to perform required operations. It can be done as described above (using various services and content marshaller helper) though that in many cases leads to code duplication in multiple listeners thus an extended support was added in 6.5 to simply use TaskContext to obtain that information.

loadTaskVariables(Task task);

Method loadTaskVariables can be used to populate both input and output variables of a given task by simple and single method call. That method is “no op” in case task variables are already set on a task.

To improve performance task variables are automatically set when they are available - usually given by caller on task service:

when task is created it usually has input variables, these variables are then set on Task instance so there is no need to use loadTaskVariables method as only task input variables are available when task is being created - applies to beforeTaskAdded and afterTaskAdded events handling

when task is completed it usually has output variables, these variables are set on a task so there is no need to use loadTaskVariables method if only task output variables are required.

Other than that loadTaskVariables should be used to populate task variables.
It’s enough to call it once (like in beforeTask) method of the listener as they will be available to both beforeTask* and afterTask* methods then.