The <transformer> element is used to create a Message-transforming endpoint. In addition to "input-channel" and "output-channel" attributes, it requires a "ref". The "ref" may either point to an Object that contains the @Transformer annotation on a single method (see below) or it may be combined with an explicit method name value provided via the "method" attribute.

The method that is used for transformation may expect either the Message type or the payload type of inbound Messages. The return value of the method can be any type. If the return value is itself a Message, that will be passed along to the transformer's output channel. If the return value is null, then no reply Message will be sent (effectively the same behavior as a Message Filter). Otherwise, the return value will be sent as the payload of a Message.