Understanding and using ActivitiEventListener: A practical guide

In Business Process Management (BPM) systems, Activiti is a powerful open-source tool that provides a wealth of features to implement complex approval workflows. The ActivitiEventListener is one of its key components. By listening to and handling various process events, you can execute custom business logic at different stages of the workflow. This article will provide a detailed overview of the ActivitiEventListener, including information on process events and node events.

ActivitiEventListener is an interface in Activiti used to listen to process events. By implementing this interface, you can capture various events that occur during process execution and handle them accordingly. For example, you can perform specific actions when events such as process start, task creation, task completion, and process end occur.

Process Events

Process events refer to events that occur throughout the lifecycle of a process. Here are some common process events:

• Process Started Event (PROCESS_STARTED): Triggered when a new process instance starts.
• Process Completed Event (PROCESS_COMPLETED): Triggered when a process instance completes normally.
• Process Cancelled Event (PROCESS_CANCELLED): Triggered when a process instance is cancelled.
• Task Created Event (TASK_CREATED): Triggered when a new task is created.
• Task Assigned Event (TASK_ASSIGNED): Triggered when a task is assigned to an approver.
• Task Completed Event (TASK_COMPLETED): Triggered when a task is completed.

Using ActivitiEventListener

To use the ActivitiEventListener, you need to implement this interface and register it with the Activiti engine.

import org.activiti.engine.delegate.event.ActivitiEvent;
import org.activiti.engine.delegate.event.ActivitiEventListener;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class MyEventListener implements ActivitiEventListener {
    private static final Logger logger = LoggerFactory.getLogger(MyEventListener.class);

    @Override
    public void onEvent(ActivitiEvent event) {
        switch (event.getType()) {
            case PROCESS_STARTED:
                logger.info("Process started: " + event.getProcessInstanceId());
                break;
            case PROCESS_COMPLETED:
                logger.info("Process completed: " + event.getProcessInstanceId());
                break;
            case TASK_CREATED:
                logger.info("Task created: " + event.getExecutionId());
                break;
            case TASK_COMPLETED:
                logger.info("Task completed: " + event.getExecutionId());
                break;
            default:
                logger.info("Other event: " + event.getType());
                break;
        }
    }

    @Override
    public boolean isFailOnException() {
        return false;
    }
}

Then, you need to register this listener when the process engine starts:

import org.activiti.engine.ProcessEngine;
import org.activiti.engine.ProcessEngines;

public class EventListenerConfig {
    public static void main(String[] args) {
        ProcessEngine engine = ProcessEngines.getDefaultProcessEngine();
        engine.getRuntimeService().addEventListener(new MyEventListener());
    }
}