The task API event handler mechanism enables you to execute any kind of logic, including a service invocation at the various task states (not just when the task is created). This tutorial demonstrated that a piece of logic, including a service, can be executed by the human task container at various human task states. This is powerful because a task can have a number of states and business requirements may call for an execution of a service only when a task is at a specific state. For example, such requirements may state that a service is invoked only when a task is escalated.
The author would like to thank Martin Smolny from WebSphere BPM Development for his review of the tutorial.