Mule error handling_rollback exception strategy
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The document discusses the rollback exception strategy in Mule. A rollback exception strategy rolls back transactions when exceptions occur to allow messages to be reprocessed. It can be used for transactional errors or unhandled exceptions. A rollback strategy may cause infinite loops, so maximum redelivery attempts and error handling flows are recommended. Transactional transports like JDBC roll messages back to original state, while reliable transports discard messages and reprocess fresh copies. The strategy differs from the default exception strategy in how it handles message payloads and exceptions.
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Mule error handling_rollback exception strategy
- 1. Mule Concepts Error Handling Rollback Exception Strategy
- 2. • A rollback exception strategy can be used to ensure that a message that throws an exception in a flow is rolled back for reprocessing. • A rollback exception strategy can be used when you cannot correct an error when it occurs in a flow. • A rollback exception strategy is normally used to handle errors that occur in a flow that involve a transaction. • If the transaction fails, that is, if a message throws an exception while being processed, then the rollback exception strategy rolls back the transaction in the flow. • If the inbound connector is transactional, Mule delivers the message to the inbound connector of the parent flow again to reattempt processing (that is, message redelivery). Rollback Exception Strategy
- 3. • When to use : – To manage transactional errors. – To manage unhandled exceptions—exceptions that the application fails to catch. – Put in flows in which messages require redelivery. • A rollback exception strategy has the potential to introduce an infinite loop of activity within a flow. • To avoid this infinite loop and responsibly manage unresolvable errors, two limitations to a rollback exception strategy can be applied: – Define the maximum number of times that the rollback exception strategy attempts to redeliver the message for processing. – Define a flow to handle messages that exceed the maximum number of redelivery attempts. Rollback Exception Strategy
- 4. • When to use : – To manage transactional errors. – To manage unhandled exceptions—exceptions that the application fails to catch. – Put in flows in which messages require redelivery. • A rollback exception strategy has the potential to introduce an infinite loop of activity within a flow. • To avoid this infinite loop and responsibly manage unresolvable errors, two limitations to a rollback exception strategy can be applied: – Define the maximum number of times that the rollback exception strategy attempts to redeliver the message for processing. – Define a flow to handle messages that exceed the maximum number of redelivery attempts. Rollback Exception Strategy
- 5. • A rollback exception strategy provides multiple attempts for a message to successfully move through a flow before committing a failed transaction and consuming the message, unlike catch exception strategy. • Mule attempts message redelivery when the flow uses one of the following two types of transports: – Transactional • consumes a message as it travels through the flow • transforms it to a different object, or enriches it with more data. • When a message using a transactional transport throws an exception, a rollback exception strategy rolls back the transaction so the transport can return a message to its original state for reprocessing. – Reliable • does not consume a message as it travels through the flow until it can ascertain that the message has successfully reached the end of the flow. • When a message using a reliable transport throws an exception, the rollback exception strategy discards the partially processed message and instructs the flow to attempt processing the original message again. Rollback Exception Strategy
- 6. • If the flow involves a reliable transport and a rollback exception strategy, you must set the flow’s Processing Strategy to "synchronous". (Configure the Processing Strategy in the Flow Properties panel.) • This is because reliable transports do not consume messages, they wait for messages to successfully complete a flow before consuming the messages; therefore, the flow must process synchronously. • If you deploy a Mule application that contains a flow with an asynchronous processing strategy and a rollback exception strategy configured for message redelivery, the application fails! Rollback Exception Strategy
- 7. – Transactional Transports : • VM – message rolls back to its original state for reprocessing. • JDBC – message rolls back to its original state for reprocessing. • JMS – message rolls back to its original state for reprocessing. – Reliable Transports : • JMS – The session recovers, that is, Mule discards the copy of the source file and attempts reprocessing the message using a fresh copy. – A JMS redelivery configuration takes precedence over the rollback exception strategy. • FTP – Mule discards the copy of the source file and attempts reprocessing the message using a fresh copy. • File – Mule discards the copy of the source file and attempts reprocessing the message using a fresh copy. • IMAP – Mule does not move the message from the mailbox and attempts reprocessing the message using a fresh copy of the original. Rollback Exception Strategy
- 8. • Unhandled Exceptions – exceptions that they are unable to resolve by performing corrective measures – Typically, all unhandled exceptions are handled by Mule’s default exception strategy – But you can customize a rollback exception strategy to more efficiently route messages with unhandled exceptions. – Below ways can be used : • For one-way pattern of flow exchange, the rollback exception strategy instructs the inbound connector transport to execute corrective actions. • For request-response pattern rollback exception strategy changes the payload of a message and returns it to the client. Rollback Exception Strategy
- 9. • Rollback Exception Strategy vs. Default Exception Strategy : – Default Exception Strategy: • Stores the exception information in the payload of the message. • Returns null in the exceptionPayload attributeMessage. • Injects NullPayload as the message’s payload; unable to customize. • Records exception information in the exceptionPayload attribute; unable to customize. – Rollback Exception Strategy: • Retains the information in the message payload at the time the exception was thrown; does not alter the message payload. • Stores the exception information in the exceptionPayload. • Returns the message processing result during execution of the exception strategy. • Records exception information in the exceptionPayload attribute; able to customize. Rollback Exception Strategy
- 10. • Configuration properties : – Display Name : • A unique name for the rollback exception strategy in your application. – Max redelivery attempts : • an integer to define the number of times you want the rollback exception strategy to roll back a message for reprocessing. • Setting is as 0 : the rollback exception strategy does _*not* _attempt to redeliver the message and throws a MessageRedeliveredException upon the first processing failure. • Setting it as nothing : he rollback exception strategy redelivers the message over and over again, creating an infinite loop. – When : • Enter an expression to indicate the kind of exception the rollback exception should handle. • Expression not defined: – All messages in this flow that throw exceptions are handled by this rollback exception strategy. • Expression defined: – When Mule evaluates the expression against the message being processed and returns true, Mule executes the exception strategy. – Mule’s default exception strategy implicitly handles all exceptions which do not match the expression you have defined in theWhen field. • Enable Notifications: – true (default) » When set to true, instructs Mule to send an exception notification to a registered listener – False » To not to send the notification. Rollback Exception Strategy