GH-3450: Expose PubSub requireSubscribers option (#3459)

* GH-3450: Expose PubSub requireSubscribers option

Fixes https://github.com/spring-projects/spring-integration/issues/3450

* Add `PublishSubscribeChannel` ctors with the `requireSubscribers` option
with a direct delegation to the same option of underlying `BroadcastingDispatcher`
* Add factory methods to the `Channels` & `MessageChannels` to expose
this new `requireSubscribers` option
* Expose an XML `require-subscribers` attribute for the `<publish-subscribe-channel`
* Document this new `requireSubscribers` option
* Introduce a global `spring.integration.channels.error.requireSubscribers` property
for a default `errorChannel`
* Document this property and explain its default `true` in the `error-handling.adoc`
* Remove docs for `spring.integration.postProcessDynamicBeans` since it purpose was
removed since version `5.1` in favor of "always post-process behavior" as it was
always with all the `BeanPostProcessor`s

* * Fix language in docs according review

* * Add more docs about `requireSubscribers` and cross-links between chapters

spring-integration-core/src/test/java/org/springframework/integration/channel/PublishSubscribeChannelTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2021 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.
@@ -16,18 +16,23 @@
 
 package org.springframework.integration.channel;
 
-import static org.assertj.core.api.Assertions.assertThat;
-import static org.assertj.core.api.Assertions.fail;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
 import static org.mockito.Mockito.mock;
 
 import java.util.concurrent.Executor;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import org.springframework.beans.factory.BeanFactory;
+import org.springframework.integration.MessageDispatchingException;
+import org.springframework.messaging.MessageDeliveryException;
+import org.springframework.messaging.support.GenericMessage;
 
 /**
  * @author Gary Russell
+ * @author Artem Bilan
+ *
  * @since 5.0
  *
  */
@@ -36,17 +41,21 @@ public class PublishSubscribeChannelTests {
 	@Test
 	public void testEarlySubscribe() {
 		PublishSubscribeChannel channel = new PublishSubscribeChannel(mock(Executor.class));
-		try {
-			channel.subscribe(m -> { });
-			channel.setBeanFactory(mock(BeanFactory.class));
-			channel.afterPropertiesSet();
-			fail("expected Exception");
-		}
-		catch (IllegalStateException e) {
-			assertThat(e.getMessage()).isEqualTo("When providing an Executor, you cannot subscribe() until the " +
-					"channel "
-					+ "bean is fully initialized by the framework. Do not subscribe in a @Bean definition");
-		}
+		channel.subscribe(m -> { });
+		channel.setBeanFactory(mock(BeanFactory.class));
+		assertThatIllegalStateException()
+				.isThrownBy(channel::afterPropertiesSet)
+				.withMessage("When providing an Executor, you cannot subscribe() until the channel "
+						+ "bean is fully initialized by the framework. Do not subscribe in a @Bean definition");
+	}
+
+	@Test
+	public void testRequireSubscribers() {
+		PublishSubscribeChannel channel = new PublishSubscribeChannel(true);
+		assertThatExceptionOfType(MessageDeliveryException.class)
+				.isThrownBy(() -> channel.send(new GenericMessage<>("test")))
+				.withCauseInstanceOf(MessageDispatchingException.class)
+				.withMessageContaining("Dispatcher has no subscribers");
 	}
 
 }

spring-integration-core/src/test/java/org/springframework/integration/channel/interceptor/GlobalChannelInterceptorTests-context.xml

@@ -3,16 +3,10 @@
 	   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 	   xmlns:int="http://www.springframework.org/schema/integration"
 	   xmlns:p="http://www.springframework.org/schema/p"
-	   xmlns:aop="http://www.springframework.org/schema/aop" xmlns:util="http://www.springframework.org/schema/util"
-	   xmlns:beans="http://www.springframework.org/schema/c"
+	   xmlns:aop="http://www.springframework.org/schema/aop"
 	   xsi:schemaLocation="http://www.springframework.org/schema/aop https://www.springframework.org/schema/aop/spring-aop.xsd
 		http://www.springframework.org/schema/integration https://www.springframework.org/schema/integration/spring-integration.xsd
-		http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd
-		http://www.springframework.org/schema/util https://www.springframework.org/schema/util/spring-util.xsd">
-
-	<util:properties id="integrationGlobalProperties">
-		<prop key="spring.integration.postProcessDynamicBeans">true</prop>
-	</util:properties>
+		http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd">
 
 	<int:channel id="inputA">
 		<int:interceptors>

spring-integration-core/src/test/java/org/springframework/integration/config/xml/ErrorChannelAutoCreationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -18,30 +18,29 @@ package org.springframework.integration.config.xml;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
-import org.junit.Test;
-import org.junit.runner.RunWith;
+import org.junit.jupiter.api.Test;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.integration.channel.PublishSubscribeChannel;
+import org.springframework.integration.test.util.TestUtils;
 import org.springframework.messaging.MessageChannel;
-import org.springframework.test.context.ContextConfiguration;
-import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
 
 /**
  * @author Oleg Zhurakousky
  * @author Artem Bilan
  */
-@ContextConfiguration
-@RunWith(SpringJUnit4ClassRunner.class)
+@SpringJUnitConfig
 public class ErrorChannelAutoCreationTests {
 
 	@Autowired
 	private MessageChannel errorChannel;
 
-	// see INT-1899
 	@Test
 	public void testErrorChannelIsPubSub() {
-		assertThat(errorChannel.getClass()).isEqualTo(PublishSubscribeChannel.class);
+		assertThat(this.errorChannel).isInstanceOf(PublishSubscribeChannel.class);
+		assertThat(TestUtils.getPropertyValue(this.errorChannel, "dispatcher.requireSubscribers", Boolean.class))
+				.isTrue();
 	}
 
 }