Mule exceptions Strategy

1. Mule Exceptions

2. Handling Exceptions
Handling Exceptions:
o An exception is an event, which occurs during the execution of a program, that disrupts the normal flow of the program.
o To continue the flow execution, we should handle the exceptions.
o There are 2 types of exceptions:
 System Exceptions:
 It is thrown at the system-level when no message is involved.
 It occurs during application start-up or when a connection to an external system fails.
 Message Exceptions:
 It is thrown within a flow whenever a message is involved.
 It occurs due to invalid data or unexpected application scenario.

3.  Handling System Exceptions:
o When a system exception occurs, a default system exception strategy is invoked.
o Default System Exception Strategy behavior:
 It handles all the system exceptions thrown in Mule applications.
 It stops execution of the flow, logs the exception & rolls back the transaction.
 It is non configurable.
o If the system exception is caused by a connection failure, then we should apply Reconnection Strategy
to continue the flow execution by retrying connection.
 Setting Reconnection Strategy:
Handling System Exceptions

4.  Handling Messaging Exceptions:
o When a messaging exception occurs, a default messaging exception strategy is invoked.
o Default Messaging Exception Strategy behavior:
 It implicitly and globally handles all messaging exceptions thrown in Mule applications.
 It stops execution of the flow, logs the exception & rolls back the transaction.
 It is non configurable.
o If a messaging exception is caused by invalid data or due to unexpected application scenario, then we
should apply our own Messaging Exception Strategy to continue the flow execution.
 Messaging Exception Strategy:
o When a message being processed through a Mule flow throws an exception:
 Normal flow execution stops.
 The message is passed to the first processor in the exception strategy.
Handing Messaging Exceptions

5. o Message Exception Strategies are added to the error handling section of a flow.
o Each Exception Strategy can contain any number of message processors.
o All flows can have their own exception strategies.
o Subflows cannot have their own exception strategies.
o If a flow does not have an exception strategy, the strategy of the calling flow is used.
o Each flow can contain only one Exception Strategy.
 Choice Exception Strategies can contain one or more catch and/or rollback exception strategies.
o Mule messaging exception strategies can be categorized in below main parts:
 Catch: Catches exceptions based on conditions.
 Rollback: Rolls back message for reprocessing.
 Choice: Selects one of multiple catch and/or rollback strategies based on condition.
 Reference: Allows us to reference globally defined strategies.
 Custom: Allows us to specify a custom class for handling the exception.
Defining Messaging Exception Strategy

6.  Flow:
 Response:
Defining Messaging Exception Strategy

7.  Defining Global Exception Strategy:
o We can reuse exception handling strategies by defining them outside a flow.
 We can drag them out and drop them outside any flow.
 Typically, we put them in our global configuration file.
o We use Reference Exception Strategy to give reference to global exception handlers.
o Default Exception Strategy can be replaced with our own Global Default Exception Strategy by
specifying in global.xml file.
Defining Global Exception Strategy