Explains how the exceptions are handled in mule, what re the different exception strategies available, and what do they do.

1. Mule Concepts
Elements in a Mule Flow :
Exception Strategies

2. • Mule provides numerous options for handling errors.
• Errors, or faults, that occur within Mule are referred
to as exceptions.
• To manage these exceptions, Mule allows you to
configure exception strategies.
• Mule’s default exception strategy — which implicitly applies
to all Mule applications — manages errors (such as, 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.
Elements in a Mule Flow:
Exception Strategies

3. • Errors that occur in Mule fall into one of two
categories:
– System Exceptions
– Messaging Exceptions.
Elements in a Mule Flow:
Exception Strategies

4. • 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.
– E.g. system exception strategies handle exceptions that occur:
• During application start-up.
• When a connection to an external system fails.
– When a system exception occurs
• Mule sends an exception notification to registered listeners
• logs the exception
• if the exception was caused by a connection failure — executes the reconnection
strategy.
– System Exception Strategies are not configurable in Mule.
– Example : Imagine Mule establishes a connection to a JMS broker in
order to receive a message. When Mule attempts to use the
connection to consume a message the connection fails, which causes
Mule to invoke the system exception strategy. Because the failure
occurred before any message was received for processing, Mule
invoked the system, rather than messaging, exception strategy.
Elements in a Mule Flow:
Exception Strategies

5. • Messaging Exceptions:
– Mule invokes a Messaging Exception Strategy whenever an exception
is thrown within a flow.
– Whenever a message is involved, exceptions are handled
by messaging exception strategies.
– When a message being processed through a Mule flow throws an
exception,
• normal flow execution stops.
• Mule transfers the message to the message processor sequence within the
exception strategy.
– You can incorporate any number of message processors into an
exception strategy to handle the exception precisely as you wish.
Elements in a Mule Flow:
Exception Strategies

6. • Messaging Exceptions:
– Below diagram displays how exception strategy behaves, when a
Messaging Exception occurs.
Elements in a Mule Flow:
Exception Strategies

7. • Mule supports five types of messaging exception
strategies, each of which is capable of handling
errors that occur in flows which process transactions.
• Below are the Exception Strategies
– Catch Exception Strategy
– Choice Exception Strategy
– Default Exception Strategy
– Reference Exception Strategy
– Rollback Exception Strategy
Elements in a Mule Flow:
Exception Strategies

8. • Catch Exception Strategy :
– Customizes the way Mule handles any exception.
– Catch exception strategies consume inbound messages, as opposed to
rolling them back.
– Transaction Error Handling :
• When a message throws an exception, the catch exception strategy alwayscommits
the transaction and consumes the message.
• Choice Exception Strategy :
– Customizes 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 :
• 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.)
Elements in a Mule Flow:
Exception Strategies

9. • Default Exception Strategy :
– Provides an implicit default to handle all messaging exceptions that
are thrown in Mule applications.
– Transaction Error Handling :
• Mule automatically rolls back any pending transaction and logs the exception.
• If no transaction is involved, the default exception strategy simply logs the
exception.
• Reference Exception Strategy :
– Refers and adheres to the error handling parameters defined in a
global catch, rollback, or choice exception strategy.
– Transaction Error Handling :
• 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.)
Elements in a Mule Flow:
Exception Strategies

10. • Rollback Exception Strategy :
– Ensures 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 :
• 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.
Elements in a Mule Flow:
Exception Strategies

11. • Characteristics of Exception Strategy :
– 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.)
– You can create one or more global exception strategies to reuse in
flows throughout your entire Mule application.
– A Transactional Scope may include its own exception strategy,
regardless of what you define at Flow level.
Elements in a Mule Flow:
Exception Strategies

12. • Example (See the Notes for flow xml):
Elements in a Mule Flow:
Exception Strategies