GH-1396: Declarables constructor is too strict

Resolves #1396

* Make constructor more flexible by upper bounded wildcard
* Review amendments

Author: bjmi

spring-amqp/src/main/java/org/springframework/amqp/core/Declarables.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2019 the original author or authors.
+ * Copyright 2018-2021 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.
@@ -30,6 +30,7 @@
  * broker using a single bean declaration for the collection.
  *
  * @author Gary Russell
+ * @author Björn Michael
  * @since 2.1
  */
 public class Declarables {
@@ -42,7 +43,7 @@ public Declarables(Declarable... declarables) {
 		}
 	}
 
-	public Declarables(Collection<Declarable> declarables) {
+	public Declarables(Collection<? extends Declarable> declarables) {
 		Assert.notNull(declarables, "declarables cannot be null");
 		this.declarables.addAll(declarables);
 	}
@@ -58,11 +59,10 @@ public Collection<Declarable> getDeclarables() {
 	 * @return the filtered list.
 	 * @since 2.2
 	 */
-	@SuppressWarnings("unchecked")
 	public <T> List<T> getDeclarablesByType(Class<T> type) {
 		return this.declarables.stream()
 				.filter(type::isInstance)
-				.map(dec -> (T) dec)
+				.map(type::cast)
 				.collect(Collectors.toList());
 	}
 

spring-amqp/src/test/java/org/springframework/amqp/core/DeclarablesTests.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2021 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.core;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * @author Björn Michael
+ * @since 2.4
+ */
+public class DeclarablesTests {
+
+	@Test
+	public void getDeclarables() {
+		List<Queue> queues = List.of(
+				new Queue("q1", false, false, true),
+				new Queue("q2", false, false, true));
+		Declarables declarables = new Declarables(queues);
+
+		assertThat(declarables.getDeclarables()).hasSameElementsAs(queues);
+	}
+
+	@Test
+	public void getDeclarablesByType() {
+		Queue queue = new Queue("queue");
+		TopicExchange exchange = new TopicExchange("exchange");
+		Binding binding = BindingBuilder.bind(queue).to(exchange).with("foo.bar");
+		Declarables declarables = new Declarables(queue, exchange, binding);
+
+		assertThat(declarables.getDeclarablesByType(Queue.class)).containsExactlyInAnyOrder(queue);
+		assertThat(declarables.getDeclarablesByType(Exchange.class)).containsExactlyInAnyOrder(exchange);
+		assertThat(declarables.getDeclarablesByType(Binding.class)).containsExactlyInAnyOrder(binding);
+		assertThat(declarables.getDeclarablesByType(Declarable.class)).containsExactlyInAnyOrder(
+				queue, exchange, binding);
+	}
+
+}