Add customizer callback for AMQP connections

This gives users of the JMS-client the opportunity to customize the
established AMQP connection and e.g. add a `BlockedListener` to the
connection.

See rabbitmq/rabbitmq-java-client#1415

Backport of rabbitmq#496

Author: jjank

src/main/java/com/rabbitmq/jms/admin/RMQConnectionFactory.java

@@ -165,6 +165,13 @@ public class RMQConnectionFactory implements ConnectionFactory, Referenceable, S
      */
     private Consumer<com.rabbitmq.client.ConnectionFactory> amqpConnectionFactoryPostProcessor = new NoOpSerializableConsumer<>();
 
+    /**
+     * For post-processing the created {@link com.rabbitmq.client.Connection}
+     *
+     * @since 2.10.0
+     */
+    private Consumer<com.rabbitmq.client.Connection> amqpConnectionPostProcessor = new NoOpSerializableConsumer<>();
+
     /**
      * Callback before sending a message.
      *
@@ -337,6 +344,10 @@ protected Connection createConnection(String username, String password, Connecti
 
         com.rabbitmq.client.Connection rabbitConnection = instantiateNodeConnection(cf, connectionCreator);
 
+        if (this.amqpConnectionPostProcessor != null) {
+            this.amqpConnectionPostProcessor.accept(rabbitConnection);
+        }
+
         ReceivingContextConsumer rcc;
         if (this.declareReplyToDestination) {
             rcc = this.receivingContextConsumer;
@@ -1033,7 +1044,7 @@ public void setHostnameVerification(boolean hostnameVerification) {
     public void setMetricsCollector(MetricsCollector metricsCollector) {
         this.metricsCollector = metricsCollector;
     }
-    
+
     public List<String> getUris() {
         return this.uris.stream().map(uri -> uri.toString()).collect(Collectors.toList());
     }
@@ -1052,6 +1063,32 @@ public void setAmqpConnectionFactoryPostProcessor(Consumer<com.rabbitmq.client.C
         this.amqpConnectionFactoryPostProcessor = amqpConnectionFactoryPostProcessor;
     }
 
+
+    /**
+     * Sets a post-processor for the created {@link com.rabbitmq.client.Connection}.
+     * <p>
+     * The post-processor is called after the {@link com.rabbitmq.client.Connection} is created and established. This callback
+     * can be used to customize the {@link com.rabbitmq.client.Connection} e.g. adding a {@link com.rabbitmq.client.BlockedListener}
+     * that emits a log message when this connection gets blocked:
+     * <pre>
+     * {@code
+     * RMQConnectionFactory factory = new RMQConnectionFactory();
+     * // ...
+     * factory.setAmqpConnectionPostProcessor(connection ->
+     *                 connection.addBlockedListener(
+     *                         reason -> log.warn("Connection blocked: {}", reason),
+     *                         () -> log.info("Connection unblocked"))
+     *         );
+     * }
+     * </pre>
+     *
+     * @param amqpConnectionPostProcessor callback that processes the AMQP connections after they are established
+     * @since 2.10.0
+     */
+    public void setAmqpConnectionPostProcessor(Consumer<com.rabbitmq.client.Connection> amqpConnectionPostProcessor) {
+        this.amqpConnectionPostProcessor = amqpConnectionPostProcessor;
+    }
+
     /**
      * Set callback called before sending a message.
      * Can be used to customize the message or the destination

src/test/java/com/rabbitmq/jms/admin/RMQConnectionFactoryTest.java

@@ -319,7 +319,8 @@ public void shouldUseSeveralAddressesWhenUrisIsUsed() throws Exception {
         assertEquals(10000, passedInAddressResolver.getAddresses().get(1).getPort());
     }
 
-    @Test public void amqpConnectionFactoryIsCalled() throws Exception {
+    @Test
+    public void amqpConnectionFactoryIsCalled() throws Exception {
         AtomicInteger callCount = new AtomicInteger(0);
         rmqCf.setAmqpConnectionFactoryPostProcessor(cf -> callCount.incrementAndGet());
         rmqCf.createConnection();
@@ -328,6 +329,16 @@ public void shouldUseSeveralAddressesWhenUrisIsUsed() throws Exception {
         assertEquals(2, callCount.get());
     }
 
+    @Test
+    public void shouldApplyConnectionCustomizer() throws Exception {
+        AtomicInteger callCount = new AtomicInteger(0);
+        rmqCf.setAmqpConnectionPostProcessor(connection -> callCount.incrementAndGet());
+        rmqCf.createConnection();
+        assertEquals(1, callCount.get(), "Connection customizer calls");
+        rmqCf.createConnection();
+        assertEquals(2, callCount.get(), "Connection customizer calls");
+    }
+
     @Test
     public void saslConfigIsSet() throws Exception {
         AtomicReference<SaslConfig> saslConfigRef = new AtomicReference<>();