INT-4455: Fix NPE in Exception router

JIRA: https://jira.spring.io/browse/INT-4455

When using java config, `setChannelMapping` NPEs due to no AC.

**cherry-pick to 4.3.x, and to master, removing AC check**

* Polishing - PR comment

* Resolve TODO in the `ErrorMessageExceptionTypeRouter`

Author: garyrussell

spring-integration-core/src/main/java/org/springframework/integration/router/ErrorMessageExceptionTypeRouter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -27,6 +27,7 @@
 import org.springframework.jmx.export.annotation.ManagedOperation;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageChannel;
+import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 
 /**
@@ -41,6 +42,7 @@
  * @author Mark Fisher
  * @author Oleg Zhurakousky
  * @author Artem Bilan
+ * @author Gary Russell
  */
 public class ErrorMessageExceptionTypeRouter extends AbstractMappingMessageRouter {
 
@@ -67,6 +69,7 @@ private void populateClassNameMapping(Set<String> classNames) {
 
 	private Class<?> resolveClassFromName(String className) {
 		try {
+			Assert.state(getApplicationContext() != null, "An ApplicationContext is required");
 			return ClassUtils.forName(className, getApplicationContext().getClassLoader());
 		}
 		catch (ClassNotFoundException e) {
@@ -78,9 +81,11 @@ private Class<?> resolveClassFromName(String className) {
 	@ManagedOperation
 	public void setChannelMapping(String key, String channelName) {
 		super.setChannelMapping(key, channelName);
-		Map<String, Class<?>> newClassNameMappings = new ConcurrentHashMap<>(this.classNameMappings);
-		newClassNameMappings.put(key, resolveClassFromName(key));
-		this.classNameMappings = newClassNameMappings;
+		if (this.initialized) {
+			Map<String, Class<?>> newClassNameMappings = new ConcurrentHashMap<>(this.classNameMappings);
+			newClassNameMappings.put(key, resolveClassFromName(key));
+			this.classNameMappings = newClassNameMappings;
+		}
 	}
 
 	@Override

spring-integration-core/src/test/java/org/springframework/integration/router/ErrorMessageExceptionTypeRouterTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -27,12 +27,15 @@
 import org.junit.Test;
 
 import org.springframework.beans.factory.support.DefaultListableBeanFactory;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
 import org.springframework.integration.MessageRejectedException;
 import org.springframework.integration.channel.QueueChannel;
 import org.springframework.integration.test.util.TestUtils;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageDeliveryException;
 import org.springframework.messaging.MessageHandlingException;
+import org.springframework.messaging.PollableChannel;
 import org.springframework.messaging.support.ErrorMessage;
 import org.springframework.messaging.support.GenericMessage;
 
@@ -43,17 +46,17 @@
  */
 public class ErrorMessageExceptionTypeRouterTests {
 
-	private DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
+	private final DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
 
-	private QueueChannel illegalArgumentChannel = new QueueChannel();
+	private final QueueChannel illegalArgumentChannel = new QueueChannel();
 
-	private QueueChannel runtimeExceptionChannel = new QueueChannel();
+	private final QueueChannel runtimeExceptionChannel = new QueueChannel();
 
-	private QueueChannel messageHandlingExceptionChannel = new QueueChannel();
+	private final QueueChannel messageHandlingExceptionChannel = new QueueChannel();
 
-	private QueueChannel messageDeliveryExceptionChannel = new QueueChannel();
+	private final QueueChannel messageDeliveryExceptionChannel = new QueueChannel();
 
-	private QueueChannel defaultChannel = new QueueChannel();
+	private final QueueChannel defaultChannel = new QueueChannel();
 
 	@Before
 	public void prepare() {
@@ -79,6 +82,7 @@ public void mostSpecificCause() {
 		router.setChannelMapping(RuntimeException.class.getName(), "runtimeExceptionChannel");
 		router.setChannelMapping(MessageHandlingException.class.getName(), "messageHandlingExceptionChannel");
 		router.setDefaultOutputChannel(defaultChannel);
+		router.afterPropertiesSet();
 
 		router.handleMessage(message);
 
@@ -101,6 +105,7 @@ public void fallbackToNextMostSpecificCause() {
 		router.setChannelMapping(RuntimeException.class.getName(), "runtimeExceptionChannel");
 		router.setChannelMapping(MessageHandlingException.class.getName(), "runtimeExceptionChannel");
 		router.setDefaultOutputChannel(defaultChannel);
+		router.afterPropertiesSet();
 
 		router.handleMessage(message);
 
@@ -122,6 +127,7 @@ public void fallbackToErrorMessageType() {
 		router.setApplicationContext(TestUtils.createTestApplicationContext());
 		router.setChannelMapping(MessageHandlingException.class.getName(), "messageHandlingExceptionChannel");
 		router.setDefaultOutputChannel(defaultChannel);
+		router.afterPropertiesSet();
 
 		router.handleMessage(message);
 
@@ -141,6 +147,7 @@ public void fallbackToDefaultChannel() {
 		ErrorMessageExceptionTypeRouter router = new ErrorMessageExceptionTypeRouter();
 		router.setApplicationContext(TestUtils.createTestApplicationContext());
 		router.setDefaultOutputChannel(defaultChannel);
+		router.afterPropertiesSet();
 
 		router.handleMessage(message);
 
@@ -163,6 +170,7 @@ public void noMatchAndNoDefaultChannel() {
 		router.setChannelMapping(MessageDeliveryException.class.getName(), "messageDeliveryExceptionChannel");
 		router.setResolutionRequired(true);
 		router.setBeanName("fooRouter");
+		router.afterPropertiesSet();
 
 		try {
 			router.handleMessage(message);
@@ -188,6 +196,7 @@ public void exceptionPayloadButNotErrorMessage() {
 		router.setChannelMapping(RuntimeException.class.getName(), "runtimeExceptionChannel");
 		router.setChannelMapping(MessageHandlingException.class.getName(), "messageHandlingExceptionChannel");
 		router.setDefaultOutputChannel(defaultChannel);
+		router.afterPropertiesSet();
 
 		router.handleMessage(message);
 
@@ -210,6 +219,7 @@ public void intermediateCauseHasNoMappingButMostSpecificCauseDoes() {
 		router.setChannelMapping(IllegalArgumentException.class.getName(), "illegalArgumentChannel");
 		router.setChannelMapping(MessageHandlingException.class.getName(), "messageHandlingExceptionChannel");
 		router.setDefaultOutputChannel(defaultChannel);
+		router.afterPropertiesSet();
 
 		router.handleMessage(message);
 
@@ -229,6 +239,7 @@ public void testHierarchicalMapping() {
 		router.setApplicationContext(TestUtils.createTestApplicationContext());
 		router.setChannelMapping(MessageHandlingException.class.getName(), "messageHandlingExceptionChannel");
 		router.setDefaultOutputChannel(defaultChannel);
+		router.afterPropertiesSet();
 
 		router.handleMessage(message);
 
@@ -241,6 +252,7 @@ public void testInvalidMapping() {
 		ErrorMessageExceptionTypeRouter router = new ErrorMessageExceptionTypeRouter();
 		router.setBeanFactory(beanFactory);
 		router.setApplicationContext(TestUtils.createTestApplicationContext());
+		router.afterPropertiesSet();
 		try {
 			router.setChannelMapping("foo", "fooChannel");
 			fail("IllegalStateException expected");
@@ -251,4 +263,28 @@ public void testInvalidMapping() {
 		}
 	}
 
+	@Test
+	public void testLateClassBinding() {
+		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(Config.class);
+		ctx.getBean(ErrorMessageExceptionTypeRouter.class).handleMessage(new GenericMessage<>(new NullPointerException()));
+		assertNotNull(ctx.getBean("channel", PollableChannel.class).receive(0));
+		ctx.close();
+	}
+
+	public static class Config {
+
+		@Bean
+		public ErrorMessageExceptionTypeRouter errorMessageExceptionTypeRouter() {
+			ErrorMessageExceptionTypeRouter router = new ErrorMessageExceptionTypeRouter();
+			router.setChannelMapping(NullPointerException.class.getName(), "channel");
+			return router;
+		}
+
+		@Bean
+		public PollableChannel channel() {
+			return new QueueChannel();
+		}
+
+	}
+
 }