Hi Camel developers, I'd like to propose an enhancement on handling data types of Camel message contents. To start a smooth discussion I implemented the idea first: https://github.com/igarashitm/camel/tree/contract-based-type-awareness
And these testcases demonstrates the declarative transformer usage according to the declared data types: [Java DSL] https://github.com/igarashitm/camel/commit/498c27d2ba99b04bbe7b90a93329d42b7c718a29#diff-c14a7e8e88a6e41492946e1537bfb1cf [Spring DSL] https://github.com/igarashitm/camel/commit/498c27d2ba99b04bbe7b90a93329d42b7c718a29#diff-b2506c84ddde91438fc6374039e21534 This adds input/output content type declaration on from and all other processors. It also introduces well-known Exchange properties, INPUT_TYPE and OUTPUT_TYPE which are used to specify the current message content type. The data type is URN like string starts with scheme, like java:org.example.ItemA or xml:{org.example.xml}ItemA. If the content type is declared via inputType/outputType/contract, the ContractProcessor wraps the actual processor and process transformation/validation according to the type, say if INPUT_TYPE exchange property has xml:{org.example.xml}ItemA and the declared inputType is xml:{org.example.xml}ItemB, then it transforms xml:{org.example.xml}ItemA content into xml:{org.example.xml}ItemB. The <transformers> element which is introduced right under the <camelContext> is the one to declare the mappings between transformer implementation and those from/to data type. I implemented only transformer first, but validator would be brought in in a same way. This way allows users to make data types visible in the route definition and keep the transformation/validation apart from route definition itself. The most important thing is that the ContractProcessor is involved only when content type is explicitly declared in a route definition, so that it never breaks existing camel routes. Ofcourse programatic transformations/validations we're doing today are still fully available. It's purely an addition to the existing camel features. Any thoughts? Does it sound acceptable to get merged into camel? ANY feedback would be really appreciated! Thanks, Tomo
