Event Message

Camel supports the Event Message from the EIP patterns by supporting the Exchange Pattern on a Message which can be set to InOnly to indicate a oneway event message. Camel Components then implement this pattern using the underlying transport or protocols.

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The default behaviour of many Components is InOnly such as for JMS, File or SEDA

See the related Request Reply message.

Using endpoint URI

If you are using a component which defaults to InOut you can override the Exchange Pattern for a consumer endpoint using the pattern property.

foo:bar?exchangePattern=InOnly
This is only possible on endpoints used by consumers (i.e. in <from>).

In the example below the message will be forced as an event message as the consumer is in InOnly mode.

from("mq:someQueue?exchangePattern=InOnly")
  .to("activemq:queue:one-way");

And with XML:

<route>
    <from uri="mq:someQueue?exchangePattern=InOnly"/>
    <to uri="activemq:queue:one-way"/>
</route>

Using setExchangePattern EIP

You can specify the Exchange Pattern using setExchangePattern in the DSL.

from("mq:someQueue")
  .setExchangePattern(ExchangePattern.InOnly)
  .to("activemq:queue:one-way");

And with XML:

<route>
    <from uri="mq:someQueue"/>
    <setExchangePattern pattern="InOnly"/>
    <to uri="activemq:queue:one-way"/>
</route>

When using setExchangePattern then the Exchange Pattern on the Exchange is changed from this point onwards in the route.

This means you can change the pattern back again at a later point:

from("mq:someQueue")
  .setExchangePattern(ExchangePattern.InOnly)
  .to("activemq:queue:one-way");
  .setExchangePattern(ExchangePattern.InOut)
  .to("activemq:queue:in-and-out")
  .log("InOut MEP received ${body}")
Using setExchangePattern to change the Exchange Pattern is often only used in special use-cases where you must force to be using either InOnly or InOut mode when using components that support both modes (such as messaging components like ActiveMQ, JMS, RabbitMQ etc.)
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