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To support various message exchange patterns like one way Event Message and Request ResponseReply messages Camel uses an Exchangehttp://activemq.apache.org/camel/maven/camel-core/apidocs/org/apache/camel/Exchange.html interface which has a pattern property which can be set to InOnly for an Event Message which has a single inbound Message, or InOut for a Request Reply where there is an inbound and outbound Message.
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