How does the Recipient List EIP work in Camel?

The Recipient List dynamically determines the list of endpoints to send a message to at runtime, based on a header or expression. Unlike Multicast (which uses a static list), the destinations are computed from the message itself. This is useful for subscription-based routing, workflow dispatch tables, and tenant-aware fan-out.

// Recipients read from a header (comma-separated URIs):
from("direct:start")
    .recipientList(header("destinations"));

// Dynamic list built using Simple:
from("direct:notify")
    .recipientList(simple("jms:queue:${header.tenantId}-alerts,http://audit.service/log"))
    .parallelProcessing();

// Stop on first exception from any recipient:
from("direct:send")
    .recipientList(header("targets")).stopOnException();

The recipients are resolved per-message. Multiple recipients can be processed in parallel with .parallelProcessing(). Responses from each recipient are discarded by default; use an AggregationStrategy to merge them. The delimiter defaults to comma but can be changed with .delimiter(string).

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