Polish

src/asciidoc/index.adoc

@@ -38645,11 +38645,10 @@ for purging inactive destinations.
 
 
 [[websocket-stomp-appplication-context-events]]
-==== Broker events and message interception
+==== Listening To ApplicationContext Events and Intercepting Messages
 
-The STOMP messaging support publishes the `ApplicationContext` events listed below.
-To subscribe to receive one or more of these events a Spring managed component can
-implement Spring's `ApplicationListener` interface. The events are:
+Several `ApplicationContext` events (listed below) are published and can be
+received by implementing Spring's `ApplicationListener` interface.
 
 * `BrokerAvailabilityEvent` -- indicates when the broker becomes available/unavailable.
 While the "simple" broker becomes available immediately on startup and remains so while
@@ -38686,82 +38685,43 @@ will typically notice the broker is not responding within 10 seconds. Clients ne
 implement their own reconnect logic.
 ====
 
-An application can also intercept all incoming or outgoing messages by creating a
-`ChannelInterceptor` and registering it on the inbound or outbound channel. See bellow
-an example that filters messages based on the message destination and user:
+Furthermore, an application can directly intercept every incoming and outgoing message by
+registering a `ChannelInterceptor` on the respective message channel. For example
+to intercept inbound messages:
 
 [source,java,indent=0]
 [subs="verbatim,quotes"]
 ----
-public class AccessControlChannelInterceptor extends ChannelInterceptorAdapter {
+  @Configuration
+  @EnableWebSocketMessageBroker
+  public class WebsocketConfig extends AbstractWebSocketMessageBrokerConfigurer {
 
     @Override
-    public Message<?> preSend(Message<?> message, MessageChannel channel) {
-      Principal user = SimpMessageHeaderAccessor.getUser(message.getHeaders());
-      String destination = SimpMessageHeaderAccessor.getDestination(message.getHeaders());
-      if(isAllowed(destination, user)) {
-        return message;
-      }
-      throw new AccessControlException("Message to destination " + destination
-          + " not allowed for user " + user.getName());
-    }
-
-    private boolean isAllowed(String destination, Principal user) {
-      // ...
+    public void configureClientInboundChannel(ChannelRegistration registration) {
+      registration.setInterceptors(new MyChannelInterceptor());
     }
   }
 ----
 
-In Java config:
+A custom `ChannelInterceptor` can extend the empty method base class
+`ChannelInterceptorAdapter` and use `StompHeaderAccessor` or `SimpMessageHeaderAccessor`
+to access information about the message.
 
 [source,java,indent=0]
 [subs="verbatim,quotes"]
 ----
-  @Configuration
-  @EnableWebSocketMessageBroker
-  public class WebsocketConfig extends AbstractWebSocketMessageBrokerConfigurer {
-
-    // ...
+  public class MyChannelInterceptor extends ChannelInterceptorAdapter {
 
     @Override
-    public void configureClientInboundChannel(ChannelRegistration registration) {
-      registration.setInterceptors(myInterceptor());
-    }
-
-    @Bean
-    public AccessControlChannelInterceptor myInterceptor() {
-      return new AccessControlChannelInterceptor();
+    public Message<?> preSend(Message<?> message, MessageChannel channel) {
+      StompHeaderAccessor accessor = StompHeaderAccessor.wrap(message);
+      StompCommand command = accessor.getStompCommand();
+      // ...
+      return message;
     }
-
   }
 ----
 
-Or in XML config:
-
-[source,xml,indent=0]
-[subs="verbatim,quotes,attributes"]
-----
-  <beans xmlns="http://www.springframework.org/schema/beans"
-    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-    xmlns:websocket="http://www.springframework.org/schema/websocket"
-    xsi:schemaLocation="
-      http://www.springframework.org/schema/beans
-      http://www.springframework.org/schema/beans/spring-beans.xsd
-      http://www.springframework.org/schema/websocket
-      http://www.springframework.org/schema/websocket/spring-websocket.xsd">
-
-    <websocket:message-broker application-destination-prefix="/app">
-      <websocket:stomp-endpoint path="/foo"/>
-      <websocket:simple-broker prefix="/topic"/>
-      <websocket:client-inbound-channel>
-        <websocket:interceptors>
-          <bean id="myInterceptor" class="com.foo.AccessControlChannelInterceptor" />
-        </websocket:interceptors>
-      </websocket:client-inbound-channel>
-    </websocket:message-broker>
-
-  </beans>
-----
 
 
 [[websocket-stomp-websocket-scope]]