If an application needs to implement customized event handling, it must implement this interface and then register it with either the Unmarshaller, or the Marshaller. The Jakarta XML Binding Provider will then report validation errors and warnings encountered during the unmarshal, marshal, and validate operations to these event handlers.

If the handleEvent method throws an unchecked runtime exception, the Jakarta XML Binding Provider must treat that as if the method returned false, effectively terminating whatever operation was in progress at the time (unmarshal, validate, or marshal).

Modifying the Java content tree within your event handler is undefined by the specification and may result in unexpected behaviour.

Failing to return false from the handleEvent method after encountering a fatal error is undefined by the specification and may result in unexpected behavior.

Default Event Handler

If the client application does not set an event handler on their Unmarshaller, or Marshaller prior to calling the validate, unmarshal, or marshal methods, then a default event handler will receive notification of any errors or warnings encountered. The default event handler will cause the current operation to halt after encountering the first error or fatal error (but will attempt to continue after receiving warnings).