One of the advantages of a messaging architecture is the ability to provide common behavior and capture meaningful information about the messages passing through the system in a non-invasive way. Since the Messages are being sent to and received from MessageChannels, those channels provide an opportunity for intercepting the send and receive operations. The ChannelInterceptor strategy interface provides methods for each of those operations:

public interface ChannelInterceptor {
    boolean preSend(Message<?> message, MessageChannel channel);
    void postSend(Message<?> message, MessageChannel channel, boolean sent);
    boolean preReceive(MessageChannel channel);
    void postReceive(Message<?> message, MessageChannel channel);
}

After implementing the interface, registering the interceptor with a channel is just a matter of calling:

channel.addInterceptor(someChannelInterceptor);

The methods that return a boolean value can return 'false' to prevent the send or receive operation from proceeding (send would return 'false' and receive would return 'null').

Because it is rarely necessary to implement all of the interceptor methods, a ChannelInterceptorAdapter class is also available for sub-classing. It provides no-op methods (the void methods are empty, and the boolean methods return true). Therefore, it is often easiest to extend that class and just implement the method(s) that you need as in the following example.

public class CountingChannelInterceptor extends ChannelInterceptorAdapter {

    private final AtomicInteger sendCount = new AtomicInteger();

    @Override
    public boolean preSend(Message<?> message, MessageChannel channel) {
        sendCount.incrementAndGet();
        return true;
    }
}