Search for "The sample example in XML DSL would be:" text for Idempotent Consumer documentation in apache_camel_development_guide.

Here in example

<property>CamelDuplicateMessage</property>

Should be replaced with

<exchangeProperty>CamelDuplicateMessage</exchangeProperty>

The latest example is provide with camel documentation here[2].

1. https://access.redhat.com/documentation/en-us/red_hat_jboss_fuse/6.3/html/apache_camel_development_guide/msgend-idempotent

2. https://github.com/apache/camel/blob/master/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/SpringIdempotentConsumerNoSkipDuplicateFilterTest.xml#L42