GH-3555: Change logger order for errorChannel (#3949)

* GH-3555: Change logger order for errorChannel

Fixes https://github.com/spring-projects/spring-integration/issues/3555

The default global `errorChannel` has a `LoggingHandler` as a subscriber.
It is subscribed without any `order` which may lose logging messages,
when another subscriber with re-throw is present.

* Set default `LoggingHandler` on the default `errorChannel` to `Ordered.LOWEST_PRECEDENCE - 100`
to give a room for custom subscribers without an `order` and still get error logged

* Add extra note in docs about an order for custom subcribers

Co-authored-by: Gary Russell <grussell@vmware.com>

Co-authored-by: Gary Russell <grussell@vmware.com>

spring-integration-core/src/main/java/org/springframework/integration/config/DefaultConfiguringBeanFactoryPostProcessor.java

@@ -36,12 +36,14 @@ import org.springframework.beans.factory.support.BeanDefinitionReaderUtils;
 import org.springframework.beans.factory.support.BeanDefinitionRegistry;
 import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
 import org.springframework.beans.factory.support.RootBeanDefinition;
+import org.springframework.core.Ordered;
 import org.springframework.core.log.LogAccessor;
 import org.springframework.integration.channel.ChannelUtils;
 import org.springframework.integration.channel.DefaultHeaderChannelRegistry;
 import org.springframework.integration.channel.MessagePublishingErrorHandler;
 import org.springframework.integration.channel.NullChannel;
 import org.springframework.integration.channel.PublishSubscribeChannel;
+import org.springframework.integration.config.xml.IntegrationNamespaceUtils;
 import org.springframework.integration.context.IntegrationContextUtils;
 import org.springframework.integration.context.IntegrationProperties;
 import org.springframework.integration.handler.LoggingHandler;
@@ -221,6 +223,7 @@ public class DefaultConfiguringBeanFactoryPostProcessor
 					BeanDefinitionBuilder.genericBeanDefinition(LoggingHandler.class,
 									() -> new LoggingHandler(LoggingHandler.Level.ERROR))
 							.addConstructorArgValue(LoggingHandler.Level.ERROR)
+							.addPropertyValue(IntegrationNamespaceUtils.ORDER, Ordered.LOWEST_PRECEDENCE - 100)
 							.getBeanDefinition());
 
 			BeanDefinitionBuilder loggingEndpointBuilder =

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

@@ -16,12 +16,17 @@
 
 package org.springframework.integration.config.xml;
 
+import java.util.Set;
+
 import org.junit.jupiter.api.Test;
 
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.core.Ordered;
 import org.springframework.integration.channel.PublishSubscribeChannel;
+import org.springframework.integration.handler.LoggingHandler;
 import org.springframework.integration.test.util.TestUtils;
 import org.springframework.messaging.MessageChannel;
+import org.springframework.messaging.MessageHandler;
 import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -43,6 +48,15 @@ public class ErrorChannelAutoCreationTests {
 				.isTrue();
 		assertThat(TestUtils.getPropertyValue(this.errorChannel, "dispatcher.ignoreFailures", Boolean.class))
 				.isTrue();
+
+		@SuppressWarnings("unchecked")
+		Set<MessageHandler> handlers =
+				TestUtils.getPropertyValue(this.errorChannel, "dispatcher.handlers", Set.class);
+
+		assertThat(handlers).first()
+				.isInstanceOf(LoggingHandler.class)
+				.extracting("order")
+				.isEqualTo(Ordered.LOWEST_PRECEDENCE - 100);
 	}
 
 }

src/reference/asciidoc/error-handling.adoc

@@ -52,6 +52,8 @@ QueueChannel errorChannel() {
 ====
 
 NOTE: The default error channel is a `PublishSubscribeChannel`.
+By default, it has a `LoggingHandler` as a subscriber with an `ERROR` logging level and subscription order as `Ordered.LOWEST_PRECEDENCE - 100`.
+If you subscribe additional consuming endpoints, that might throw an exception, and you don't want to preempt the logging, ensure that the additional handlers have a higher order.
 
 The most important thing to understand here is that the messaging-based error handling applies only to exceptions that are thrown by a Spring Integration task that is executing within a `TaskExecutor`.
 This does not apply to exceptions thrown by a handler that operates within the same thread as the sender (for example, through a `DirectChannel` as described earlier in this section).