Message Transformers play a very important role in enabling the loose-coupling of Message Producers and Message Consumers. Rather than requiring every Message-producing component to know what type is expected by the next consumer, Transformers can be added between those components. Generic transformers, such as one that converts a String to an XML Document, are also highly reusable. For some systems, it may be best to provide a Canonical Data Model, but Spring Integration's general philosophy is not to require any particular format. Rather, for maximum flexibility, Spring Integration aims to provide the simplest possible model for extension. As with the other endpoint types, the use of declarative configuration in XML and/or Annotations enables simple POJOs to be adapted for the role of Message Transformers. These configuration options will be described below. For the same reason of maximizing flexibility, Spring does not require XML-based Message payloads. Nevertheless, the framework does provide some convenient Transformers for dealing with XML-based payloads if that is indeed the right choice for your application. For more information on those transformers, see .

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.

The @Transformer annotation can also be added to methods that expect either the Message type or the message payload type. The return value will be handled in the exact same way as described above in the section describing the <transformer> element. @Transformer Order generateOrder(String productId) { return new Order(productId); } Transformer methods may also accept the @Header and @Headers annotations. For example, one of those annotations may complement the payload Object as an additional parameter: @Transformer Order generateOrder(String productId, @Header("customerName") String customer) { return new Order(productId, customer); }