MuleESB / Apache Camel Interview Questions

How does the Wire Tap EIP work and what is it used for?

The Wire Tap sends a copy of the current message to a secondary endpoint asynchronously while allowing the original message to continue through the route unchanged. It is used for auditing, logging to an append-only store, event sourcing side-channels, and monitoring without adding latency to the main processing path.

from("jms:queue:orders")
    .wireTap("jms:topic:audit-log")   // async copy to audit log
    .to("direct:process-order");         // main flow continues

// Wire tap with body transformation for the copy:
from("direct:payment")
    .wireTap("jms:queue:payment-audit")
        .newExchangeBody(simple("Order ${header.orderId} received at ${date:now:yyyy-MM-dd}"))
    .to("direct:process-payment");

The wire tap sends a shallow copy of the Exchange with a new thread from the routing thread pool. The original Exchange continues immediately — there is no waiting for the tap. In Camel 3.x the tap always uses InOnly semantics; any response from the tap endpoint is discarded. The tap copy shares message headers with the original by default; use newExchangeBody() or onPrepare() to customise the tap message.

What is the main purpose of the Wire Tap EIP in Apache Camel? To route messages to two endpoints and aggregate the responses

✗ Try again — aggregating responses is the Multicast+AggregationStrategy pattern.

To asynchronously send a copy to a secondary endpoint while the main flow continues unchanged

✓ Well done! Wire Tap is used for auditing and monitoring without adding latency to the main path.

To hold messages until the downstream system is ready

✗ Try again — that describes a queue or a Hold/Resume pattern.

What happens to the response from the wire tap endpoint? It is merged back into the main Exchange body

✗ Try again — wire tap always uses InOnly; the response is discarded.

It is discarded — the tap endpoint always uses InOnly semantics

✓ Well done! Camel 3.x wire tap always uses InOnly; no reply is expected.

It replaces the original message body in the main flow

✗ Try again — the main flow is completely independent of the tap.

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MuleESB / Apache Camel Interview Questions

How does the Wire Tap EIP work and what is it used for?

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