# Error Event
The **Error Event** is used to handle **exceptions or runtime errors** that occur during the execution of an activity within a business process.\
It allows the process to **react gracefully to failures** by triggering alternative actions instead of abruptly stopping execution.
In the Process Template Diagram, an Error Event is represented by an **error icon**, as shown below.
***
### Purpose
**Error Events** are designed to handle **unexpected failures** or **business/system exceptions** during process execution.
They can be used to:
* Capture errors thrown by activities (e.g. Java Task, Web Service Task, Database Task)
* Trigger alternative flows such as error handling or notification
* Prevent the entire process from terminating due to a single failure
* Provide controlled recovery or escalation mechanisms
#### Example scenario
* A **Java Task** fails due to an exception
* An **Error Boundary Event** attached to the task is triggered
* The process automatically executes an error‑handling path, such as:
* Logging the error
* Sending a notification
* Invoking a compensation or cleanup task
***
### Error Event as a Boundary Event
The Error Event is commonly used as a **Boundary Event**, meaning:
* It is **attached to an activity node**
* It is triggered only when an exception occurs within that activity
* It redirects execution to an **alternative error‑handling path**
This allows exception logic to be defined **locally at the activity level**, instead of globally across the process.
***
### Error Event Configuration Overview
The Error Event configuration panel contains **one main tab**:
1. **Error**
***
### Error Tab
The **Error** tab is used to define which exceptions should be handled by this Error Event.
#### Error Properties
| Property | Mandatory | Description |
| --------- | --------- | --------------------------------------------------- |
| Exception | Yes | Type of exception that this Error Event will handle |
***
### Managing Exceptions
Within the **Error** tab, users can:
* Click **Add Exception Row** to define additional exceptions
* Click **Delete** to remove an existing exception
* Configure multiple exception types for a single Error Event
This allows fine‑grained control over which errors trigger specific handling logic.
***
### Mapping Parameters for Error Events
The **Open Mapping Parameter** button is used to map:
* Error details into process variables
* Exception data into Business Objects
When **Open Mapping Parameter** is clicked:
* The system navigates to the **Mapping Parameter** screen
* Users can map:
* **Mapping Parameter Input**
* **Mapping Parameter Output**
This makes exception information available for downstream error‑handling activities (e.g. logging, notifications, compensations).
***
### Usage Guidelines
* Attach Error Events to activities that may throw runtime exceptions
* Clearly define which exceptions should be handled
* Avoid catching overly generic exceptions unless necessary
* Always design a clear error‑handling path to prevent dead‑ends
* Use Business Object mapping to pass meaningful error information
***
### Summary
The **Error Event** enables structured and controlled **exception handling** in ONEWEB Process Designer.
Key points:
* Handles runtime errors during task execution
* Commonly used as a Boundary Event
* Triggers alternative error‑handling flows
* Supports multiple exception definitions
* Enables data mapping for error context
Proper use of Error Events ensures that business processes are **robust, fault‑tolerant, and production‑ready**, even when unexpected failures occur.
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