Service activators are one of the simplest and most useful endpoints—a plain java class whose methods can be invoked on the messages received on a channel. Service activators can either terminate the message processing or pass it on to the next channel for further processing. Let's have a look at the following example. We would like to do some validation or business logic before passing the message on to the next channel. We can define a Java class and annotate it as follows:

@MessageEndpoint
public class PrintFeed {
  @ServiceActivator
  public String upperCase(String input) {
    //Do some business processing before passing the message
    return "Processed Message";
  }
}

In our XML, we can attach the class to a channel so that it processes each and every message on it:

<int:service-activator input-channel="printFeedChannel" ref="printFeed" output-channel="printFeedChannel" />

Let's quickly go through the elements used in the preceding declaration: