Catching errors by using error boundary events

An error intermediate event that is attached to the boundary of an activity is called an error boundary event. When you attach an error boundary to an activity in a service flow or heritage human service, the event catches errors and receives error data from the activity it is attached to. The error boundary event is triggered while the activity is running and interrupts the execution of the service at that step.

To add an error boundary event to an activity in a service flow or heritage human service, complete the following steps:

1. Open the appropriate process application in the Designer view.
2. From the IBM® Process Designer library, create or open the service that you want to work with. To create the service, see Creating a service flow or Building a heritage human service.
   The service opens in the Process Designer.
3. In the Diagram view, drag an error event onto the activity node.
   The error event attaches itself to the boundary of the activity.
4. Select the error boundary event and, on the Implementation tab, under Error Properties, select Catch all errors or Catch specific errors to specify the type of errors you want the error event to catch.
5. If you selected Catch specific errors, click the pickers next to Error code and Error mapping to filter on the error code for the specific errors that can be caught and map the error data to a local variable.
   If you have a service task that uses an external service to invoke a web service, the external service might have faults based on the WSDL definition. You can choose to catch and handle errors that are related to these specific faults.

   Note: The error data cannot be mapped to a variable that is of a list type. If you want to pass information that has the structure of a sequence as error data, create a business object that contains a parameter that is of a list type and then use this business object as the variable's type.
6. Connect the error boundary event to the logic you want to run when the error occurs.
   For example, if your service flow invokes a REST service, wire your catch all error event to a script task that handles HTTP errors that the REST service returns. The error information returned by the REST service is returned in the RESTResponseException node in the tw.system.error variable:

   <error type="com.ibm.bpm.externalservice.rest.api.UnexpectedRESTResponseException" 
          description="UnexpectedRESTResponseException">
       <HTTPHeaderNames type="java.util.Collection" description="HTTPHeaderNames"></HTTPHeaderNames>
       <HTTPStatus type="java.lang.Integer" description="Integer">500</HTTPStatus>
       <RESTResponseException type="com.ibm.bpm.externalservice.rest.api.RestResponseData" description="RestResponseData">
           <HTTPStatusCode type="java.lang.Integer" description="Integer">409</HTTPStatusCode>
           <HTTPStatusMessage type="java.lang.String" description="String">Conflict</HTTPStatusMessage>
           <content type="java.lang.String" description="String">{
               "code" : 409,
               "error" : "Classifier not ready",
               "description" : "The classifier is not ready. The status of the classifier is 'Training'."
               }
           </content>
       </RESTResponseException>
       <cause type="java.lang.Throwable" description="cause"></cause>
       <localizedMessage type="java.lang.String" 
                         description="String">CWXSD1028E: The operation classify_get with HTTP method GET returned an unexpected response status code 409 with response message Conflict
       </localizedMessage>
       <message type="java.lang.String" 
                description="String">CWXSD1028E: The operation classify_get with HTTP method GET returned an unexpected response status code 409 with response message Conflict
       </message>
       <messageKey type="java.lang.String" description="String">Api.UnexpectedResponseStatus</messageKey>
       ...
   </error>

   Your JavaScript can access the HTTPStatusCode, HTTPStatusMessage, and content elements of the RESTResponseException node in the tw.system.error variable. For example, to test whether the REST service returned an HTTP status code 404, use the following statement in your script task implementation:

   if (tw.system.error.RESTResponseException[0].HTTPStatusCode[0].getText()=='404') { ... }

7. Click Save or Finish Editing.