Camunda's execution listener and task listener are listeners for adding custom logic. The difference between them is the difference between the action object and the trigger event.
Execution listeners are associated with various process elements (such as start events, user tasks, service tasks, gateways, etc.) in the BPMN process. Execution listeners can add custom logic before or after execution of process elements, or when exceptions are thrown, such as parameter validation before service task execution, and decision evaluation after gateway execution.
Task listeners are associated with task nodes and are used to listen to events such as task creation, assignment, and completion. The task listener can add custom logic in the life cycle of the task node, such as sending a notification email when the task is completed, and setting the task priority when the task is created.
Here are some use cases to illustrate when to use execution listeners and task listeners:
1. Applicable to the scenario of executing the listener:
Parameters are validated before service tasks are executed to ensure correct input;
decisions are evaluated after gateway execution to determine which branch should be executed next;
permissions are validated before user tasks are executed to ensure that users are authorized Execute the task;
record the exception information when an exception is thrown for subsequent processing.
2. Scenarios applicable to the task listener:
send notification emails when the task is completed to notify relevant personnel that the task has been completed;
set the task priority when the task is created to specify the urgency of the task;
update the task information when the task is assigned, For example, setting task deadlines, setting task handlers, etc.
In short, execution listeners and task listeners can be flexibly used according to specific business needs to add custom logic and behavior to improve the scalability and reusability of the process.