Anypoint Studio - Mule ESB Error Handling
- 1. Manirathnam G Anypoint Studio – Mule ESB Error Handling
- 2. Index Filter Types Error Handling System Exception Messaging Exception Messaging Exception – Types of Strategies Messaging Exception Strategies - Characteristics Other Ways of Handling Errors
- 3. Error Handling Introduction Mule ESB provides numerous options for handling errors. Faults that occur within Mule are referred to as exceptions; When an activity in Mule instance fails, Mule throws an exception. To manage these exceptions, Mule allows to configure exception strategies. Mule’s default exception strategy — which implicitly applies to all Mule applications — manages errors (i.e. thrown exceptions) in Mule flows. When flows require more sophisticated error management, can implement one or more exception strategies to construct precise, efficient protocols for handling errors. From a high level perspective, errors that occur in Mule fall into one of two categories: System Exceptions, and Messaging Exceptions
- 4. System Exception • 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 • When a system exception strategy occurs, Mule sends an exception notification to registered listeners, logs the exception, and — if the exception was caused by a connection failure — executes the reconnection strategy. System Exception Strategies are not configurable in Mule. Example Scenario: 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. System Exception
- 5. Messaging Exception • 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 strategies). • When a message being processed through a Mule flow throws an exception, normal flow execution stops and processes transfers to the message processor sequence within the exception strategy. We can incorporate any number of message processors – and in one case, other exception strategies – into an exception strategy to handle the exception precisely. Messaging Exception
- 6. Messaging Exception – Types of Strategies Exception Strategy Use Transaction Error Handling Default exception strategy Defined and implicitly applied by default to handle all messaging exceptions that are thrown in Mule applications When a message throws an exception, the default exception strategy rolls back the message and logs the exception. Catch exception strategy Define a catch exception strategy to customize the way Mule handles any exception. Catch exception strategies consume inbound messages. (Mule’s catch exception strategy behavior is similar to a Java catch block.) When a message throws an exception, the catch exception strategy always commits the transaction and consumes the message. Rollback exception strategy 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. 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.
- 7. Messaging Exception – Types of Strategies (Contd) Exception Strategy Use Transaction Error Handling Reference exception strategy Define a reference exception strategy to refer and adhere to the error handling parameters defined in a global catch, rollback or choice exception strategy. 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.) Choice exception strategy 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. 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.)
- 8. Messaging Exception Strategies - Characteristics 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.)
- 9. Other Ways of Handling Errors Until Successful Scope Until Successful behaves similarly to a rollback exception strategy. This scope attempts to route a message through its child flow until the message is processed successfully. However, we can define the maximum number of processing attempts the Until Successful scope undertakes before it reverts to handling the message as though it were an exception. We can configure a Failure Expression, an Ack Expression, or a Dead Letter Queue Reference to instruct the scope on how to manage messages that it cannot process. In this respect, Until Successful scope behavior is similar to a rollback exception strategy. Exception Filter Mule’s Exception filter stops normal flow execution when it discovers a message that contains a message in the “exceptionPayload” field. By comparison, an exception strategy typically stops normal flow execution when a message throws an exception in the flow. We can combine the two and configure the exception filter to stop normal flow execution and throw an exception, which triggers the exception strategy.
- 10. Other Ways of Handling Errors (Contd) Reconnection Strategies Mule’s Reconnection Strategies specify how a connector behaves when its connection fails. We can control how Mule attempts to reconnect by specifying a number of criteria: the type of exception, the number and frequency of reconnection attempts, the notifications generated, and more. With a reconnection strategy, can better control the behavior of a failed connection by configuring it, for example, to reattempt the connection only once every 15 minutes, and to stop trying to reconnect after 10 attempts. Reconnection strategy behavior resembles that of exception strategies, but reconnection strategies provide instructions specifically for — and limited to — reconnection attempts. Eg: <jms:activemq-connector name="AMQConnector"><reconnect count="5" frequency="1000"/></jms:activemq- connector> CXF Error Handling Web services that utilize CXF can implement Mule exception strategies (such as the Catch and Rollback exception strategies) that are compatible with CXF.
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