6.3. Transformations between Contracts

Transformation between contracts is necessary when a message flows in SwitchYard, and there are different types in the contracts on both ends of the channel. Implicit or explicit transformations happen wherever necessary. The extension points define how the transformation between types in contracts must happen.

Composite Service Binding and Composite Service / Composite Reference and Composite Reference Binding

Contract differences are handled in the ServiceHandlers when composing and decomposing the SwitchYard message. Any difference in contracts is handled in the Message composer.

Note
Camel and HttpMessageComposers carry out Camel Implicit Transformations if required. If target type is JAXB, the class must have @XMLRootElement annotation.

Composite Service and Component Service / Component Reference and Composite Reference

Contract differences are handled by transformers defined in the composite application, which are applied by the ExchangeHandler chain during the execution of the Exchange. The transformers usually map from an origin type to a destination type.

When the Exchange is between a composite service and a component service:
  • In the IN phase, from is the argument’s type of the composite service and the to is the type in the component service.
  • In the OUT phase, from is the return/exception type of the component service and the to is the return/exception type of the composite service.
When the Exchange is between a component reference and a composite reference:
  • In the IN phase, from is the argument’s type of the component reference and the to is the type in the composite reference.
  • In the OUT phase, from is the return/exception type of the composite reference and the to is the return/exception type of the component reference.
Note
Some implicit transformations happen (without declaring a transformer) if SwitchYard supports automatic transformation between both types, as declared by Camel Transformer.

Component Service and Component Reference

Contract differences are handled in the component implementation, and has to be explicitly transformed.

Important
  • If a Composite Service does not declare a contract, it uses the contract defined by the promoted Component Service.
  • Every Component can have one Service.
  • Binding name can be null. In this case, a binding name is automatically generated with "ServiceName+BindingType+i".
  • When the input parameter of a service contract is empty, the message does not change, it is in its original form (e.g. java.io.Reader for streaming bindings like http, File,…​)