MuleESB / Apache Camel Interview Questions

What are the error handling strategies in Camel (DefaultErrorHandler, DeadLetterChannel, TransactionErrorHandler)?

Camel provides three built-in error handler implementations, configurable per-route via errorHandler(...):

Camel Error Handler Comparison
Handler	Retries	Use case
DefaultErrorHandler	Configurable (default 0)	Non-transactional routes that log failures.
DeadLetterChannel	Configurable (default 0)	Routes needing guaranteed delivery to a DLQ after retries exhausted.
TransactionErrorHandler	Driven by transaction manager	JMS/JDBC transactional routes requiring rollback on failure.
NoErrorHandler	None	Testing or scenarios where all error handling is done manually.

// Default (no-DLQ): log on failure
errorHandler(defaultErrorHandler()
    .maximumRedeliveries(2)
    .redeliveryDelay(500));

// Dead Letter Channel
errorHandler(deadLetterChannel("jms:queue:DLQ")
    .maximumRedeliveries(3)
    .backOffMultiplier(2.0)
    .useOriginalMessage());

// Transactional error handler
errorHandler(transactionErrorHandler(transactionManager)
    .maximumRedeliveries(3)
    .redeliveryDelay(1000));

Error handlers can be scoped globally (in the parent RouteBuilder configure() or in a shared class) or per-route (placed at the start of a specific configure() method). Global scope applies to all routes defined in that builder. For per-exception handling, use onException() on top of any error handler to add targeted retry/routing logic for specific exception types.

Which Camel error handler should you use when the route must guarantee message delivery to a DLQ after all retries are exhausted? DefaultErrorHandler

✗ Try again — DefaultErrorHandler logs failures but does not route to a DLQ.

DeadLetterChannel

✓ Well done! DeadLetterChannel routes the Exchange to a dead-letter endpoint after retries are exhausted.

NoErrorHandler

✗ Try again — NoErrorHandler suppresses all error handling.

Which error handler is required for transactional JMS/JDBC routes that must roll back on failure? DeadLetterChannel with transacted=true URI option

✗ Try again — transacted=true is a JMS endpoint option, not an error handler configuration.

TransactionErrorHandler

✓ Well done! TransactionErrorHandler integrates with a Spring PlatformTransactionManager to roll back on exception.

DefaultErrorHandler with rollbackOnException(true)

✗ Try again — DefaultErrorHandler does not integrate with JTA/JMS transactions.

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MuleESB / Apache Camel Interview Questions

What are the error handling strategies in Camel (DefaultErrorHandler, DeadLetterChannel, TransactionErrorHandler)?

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