Interception

Events provide notifications for the lifecycle of a STOMP connection but not for every client message. Applications can also register a ChannelInterceptor to intercept any message and in any part of the processing chain. The following example shows how to intercept inbound messages from clients:

Java
Kotlin

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfiguration implements WebSocketMessageBrokerConfigurer {

	@Override
	public void configureClientInboundChannel(ChannelRegistration registration) {
		registration.interceptors(new MyChannelInterceptor());
	}
}

@Configuration
@EnableWebSocketMessageBroker
class WebSocketConfiguration : WebSocketMessageBrokerConfigurer {

	override fun configureClientInboundChannel(registration: ChannelRegistration) {
		registration.interceptors(MyChannelInterceptor())
	}
}

A custom ChannelInterceptor can use StompHeaderAccessor or SimpMessageHeaderAccessor to access information about the message, as the following example shows:

Java
Kotlin

public class MyChannelInterceptor implements ChannelInterceptor {

	@Override
	public Message<?> preSend(Message<?> message, MessageChannel channel) {
		StompHeaderAccessor accessor = StompHeaderAccessor.wrap(message);
		StompCommand command = accessor.getCommand();
		// ...
		return message;
	}
}

class MyChannelInterceptor : ChannelInterceptor {

	override fun preSend(message: Message<*>, channel: MessageChannel): Message<*> {
		val accessor = StompHeaderAccessor.wrap(message)
		val command = accessor.command
		// ...
		return message
	}
}

Applications can also implement ExecutorChannelInterceptor, which is a sub-interface of ChannelInterceptor with callbacks in the thread in which the messages are handled. While a ChannelInterceptor is invoked once for each message sent to a channel, the ExecutorChannelInterceptor provides hooks in the thread of each MessageHandler subscribed to messages from the channel.

Note that, as with the SessionDisconnectEvent described earlier, a DISCONNECT message can be from the client or it can also be automatically generated when the WebSocket session is closed. In some cases, an interceptor may intercept this message more than once for each session. Components should be idempotent with regard to multiple disconnect events.