The API for performing splitting consists from one base class, AbstractMessageSplitter, which is a MessageConsumer implementation, encapsulating features which are common to splitters, such as filling in the appropriate message headers CORRELATION_ID, SEQUENCE_SIZE, and SEQUENCE_NUMBER on the messages that are produced. This allows to track down the messages and the results of their processing (in a typical scenario, these headers would be copied over to the messages that are produced by the various transforming endpoints), and use them, for example, in a Composed Message Processor scenario.
An excerpt from AbstractMessageSplitter can be seen below:
public abstract class AbstractMessageSplitter
extends AbstractReplyProducingMessageConsumer {
...
protected abstract Object splitMessage(Message<?> message);
}For implementing a specific Splitter in an application, a developer can extend AbstractMessageSplitter and implement the splitMessage method, thus defining the actual logic for splitting the messages. The return value can be one of the following:
a Collection (or subclass thereof) or an array of Message objects - in this case the messages will be sent as such (after the CORRELATION_ID, SEQUENCE_SIZE and SEQUENCE_NUMBER will be populated). Using this approach gives more control to the developer, for example for populating custom message headers as part of the splitting process.
a Collection (or subclass thereof) or an array of non-Message objects - works like the prior case, except that each collection element will be used as a Message payload. Using this approach allows to focus on the
a Message or non-Message object (but not a Collection or an Array) - it works like the previous cases, except that there is a single message to be sent out.
In Spring Integration, any POJO can implement the splitting algorithm, provided that it defines a method that accepts a single argument and has a return value. In this case, the return value of the method will be interpreted as described above. The input argument might either be a Message or a simple POJO. In the latter case, the splitter will receive the payload of the incoming message.