Mule ESB provides options for handling errors through exception strategies. The default exception strategy handles errors globally by rolling back transactions and logging exceptions. Additional exception strategies like catch, rollback, and choice strategies can be used to customize error handling for specific flows. Messaging exceptions are thrown when errors occur during message processing, while system exceptions handle errors outside of message processing like during application startup.

1. Mule ESB – Error Handling

2. Mule ESB provides numerous options for handling errors.
Faults that occur within Mule are referred to as exceptions;
when an activity in your Mule instance fails, Mule throws an
exception. To manage these exceptions, Mule allows you to
configure exception strategies.

3. Default exception strategy
 It implicitly applies to all Mule applications — manages
errors (i.e. thrown exceptions) in Mule flows. When your
flows require more sophisticated error management, you can
implement one or more exception strategies to construct
precise, efficient protocols for handling errors.
 Mule ESB’s default exception strategy implicitly and globally
handles all messaging exceptions that are thrown in Mule
applications. You can override Mule’s default exception
strategy by adding a catch, rollback, or choice exception
strategy to a flow. Otherwise, when an exception is thrown in
a flow, Mule automatically rolls back any pending transaction
and logs the exception; if no transaction is involved, the
default exception strategy simply logs the exception.

4. Error Types :
1. System Exceptions
 Mule invokes a System Exception Strategy when an
exception is thrown at the system-level (i.e., when no
message is involved, exceptions are handled by system
exception strategies). For example, system exception
strategies handle exceptions that occur:
 During application start-up
 When a connection to an external system fails

5. 2. Messaging Exceptions :
Mule invokes a Messaging Exception Strategy whenever an
exception is thrown within a flow (i.e., whenever a message is
involved, exceptions are handled by messaging exception
 When a message being processed through a Mule flow throws
exception, normal flow execution stops and processes transfers
the message processor sequence within the exception strategy.
You can incorporate any number of message processors – and in
one case, other exception strategies – into an exception strategy
to handle the exception precisely as you wish. The diagram
illustrates what happens when a message throws an exception.

6. Messaging Exceptions Flow :

7. Types of messaging exception strategies :
 Default Exception Strategy
 Catch exception strategy
 Rollback exception strategy
 Reference exception strategy
 Choice exception strategy

8. Default Exception Strategy :
Use :
 Defined and implicitly
applied by default to
handle all messaging
exceptions that are thrown
in Mule applications
Transaction Error
Handling :
 When a message throws
an exception, the default
exception strategy rolls
back the message and logs
the exception.

9. Catch Exception Strategy :
Use :
 When a message throws
an exception, the default
exception strategy rolls
back the message and logs
the exception.
Transaction Error
Handling :
 When a message throws
an exception, the catch
exception
strategyalways commits
the transaction and
consumes the message.

10. Rollback Exception Strategy :
Use :
 Define a rollback exception
strategy to ensure that a
message that throws an
exception in a flow is
rolled back for
reprocessing (if the
message source supports
redelivery). Rollback
exception strategies do
not consume inbound
messages.
Transaction Error
Handling :
 When a message throws an
exception, the rollback
exception strategy makes
one or more attempts to
rollback the message and
redeliver it for processing (if
the message source
supports redelivery). If the
message exceeds its
redelivery attempts, then
the rollback exception
strategy commits the failed
transaction and consumes
the message.

11. Reference Exception Strategy :
Use :
 Define a reference
exception strategy to refer
and adhere to the error
handling parameters
defined in a global catch,
rollback or choice
exception strategy.
Transaction Error
Handling :
 When a message throws an
exception, the reference
exception strategy refers
and adheres to the error
handling parameters
defined in a global catch,
rollback or choice exception
strategy. (The reference
exception strategy itself
never actually performs any
rollback, commit, or
consume activities.)

12. Choice Exception Strategy :
Use :
 Define a choice exception
strategy to customize the
way Mule handles a
message that throws an
exception based on the
message’s content at the
moment it throws the
exception.
Transaction Error
Handling :
 When a message throws
an exception, the choice
exception strategy makes
a decision about where to
route the message for
further processing. (The
choice exception strategy
itself never actually
performs any rollback,
commit, or consume
activities.)

13. Characteristics of messaging exception strategies:
 Each flow can contain only one exception strategy.
 Each exception strategy can contain any number of
message processors.
 Choice exception strategies can contain one or more catch
and/or rollback exception strategies. (Rollback and catch
exception strategies cannot, however, contain other
exception strategies.)

14. Thank Q