GH-1517: Docs and Polishing for Composite Cust.

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/config/CompositeContainerCustomizer.java

@@ -1,23 +1,52 @@
+/*
+ * Copyright 2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package org.springframework.amqp.rabbit.config;
 
+import java.util.ArrayList;
 import java.util.List;
+
 import org.springframework.amqp.rabbit.listener.MessageListenerContainer;
 import org.springframework.util.Assert;
 
 /**
- * Implementation of {@link ContainerCustomizer<C>} providing the configuration of multiple customizers at the same time.
+ * Implementation of {@link ContainerCustomizer<C>} providing the configuration of
+ * multiple customizers at the same time.
+ *
+ * @param <C> the container type.
+ *
+ * @author Rene Felgentraeger
+ * @author Gary Russell
  */
 public class CompositeContainerCustomizer<C extends MessageListenerContainer> implements ContainerCustomizer<C> {
 
-	private final List<ContainerCustomizer<C>> customizers;
+	private final List<ContainerCustomizer<C>> customizers = new ArrayList<>();
 
+	/**
+	 * Create an instance with the provided delegate customizers.
+	 * @param customizers the customizers.
+	 */
 	public CompositeContainerCustomizer(List<ContainerCustomizer<C>> customizers) {
 		Assert.notNull(customizers, "At least one customizer must be present");
-		this.customizers = customizers;
+		this.customizers.addAll(customizers);
 	}
 
 	@Override
 	public void configure(C container) {
 		customizers.forEach(c -> c.configure(container));
 	}
+
 }

spring-rabbit/src/test/java/org/springframework/amqp/rabbit/config/CompositeContainerCustomizerTests.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.amqp.rabbit.config;
+
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.amqp.rabbit.listener.MessageListenerContainer;
+
+/**
+ * @author Gary Russell
+ * @since 2.4.8
+ *
+ */
+public class CompositeContainerCustomizerTests {
+
+	@SuppressWarnings("unchecked")
+	@Test
+	void allCalled() {
+		ContainerCustomizer<MessageListenerContainer> mock1 = mock(ContainerCustomizer.class);
+		ContainerCustomizer<MessageListenerContainer> mock2 = mock(ContainerCustomizer.class);
+		CompositeContainerCustomizer<MessageListenerContainer> cust = new CompositeContainerCustomizer<>(
+				List.of(mock1, mock2));
+		MessageListenerContainer mlc = mock(MessageListenerContainer.class);
+		cust.configure(mlc);
+		verify(mock1).configure(mlc);
+		verify(mock2).configure(mlc);
+	}
+
+}

src/reference/asciidoc/amqp.adoc

@@ -2598,6 +2598,8 @@ NOTE: For information to help you choose between `SimpleRabbitListenerContainerF
 Starting wih version 2.2.2, you can provide a `ContainerCustomizer` implementation (as shown above).
 This can be used to further configure the container after it has been created and configured; you can use this, for example, to set properties that are not exposed by the container factory.
 
+Version 2.4.8 provides the `CompositeContainerCustomizer` for situations where you wish to apply multiple customizers.
+
 By default, the infrastructure looks for a bean named `rabbitListenerContainerFactory` as the source for the factory to use to create message listener containers.
 In this case, and ignoring the RabbitMQ infrastructure setup, the `processOrder` method can be invoked with a core poll size of three threads and a maximum pool size of ten threads.