INT-3549 Fix AMQP o-c-a Validation

JIRA: https://jira.spring.io/browse/INT-3549

`afterPropertiesSet()` checks for `NullChannel` to determine
whether a correlation expression is needed for confirms.

This code fails when `nullChannel` is proxied.

Extract the type before testing.

Author: garyrussell

spring-integration-amqp/src/main/java/org/springframework/integration/amqp/outbound/AmqpOutboundEndpoint.java

@@ -196,9 +196,11 @@ protected void doInit() {
 			}
 		}
 		else {
-			Assert.state(this.confirmAckChannel == null || this.confirmAckChannel instanceof NullChannel,
+			NullChannel nullChannel = extractTypeIfPossible(this.confirmAckChannel, NullChannel.class);
+			Assert.state(this.confirmAckChannel == null || nullChannel != null,
 					"A 'confirmCorrelationExpression' is required when specifying a 'confirmAckChannel'");
-			Assert.state(this.confirmNackChannel == null || this.confirmNackChannel instanceof NullChannel,
+			nullChannel = extractTypeIfPossible(this.confirmNackChannel, NullChannel.class);
+			Assert.state(this.confirmNackChannel == null || nullChannel != null,
 					"A 'confirmCorrelationExpression' is required when specifying a 'confirmNackChannel'");
 		}
 		if (this.returnChannel != null) {

spring-integration-core/src/main/java/org/springframework/integration/context/IntegrationObjectSupport.java

@@ -21,6 +21,8 @@
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
+import org.springframework.aop.TargetSource;
+import org.springframework.aop.framework.Advised;
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
@@ -229,6 +231,28 @@ protected <T> T getIntegrationProperty(String key, Class<T> tClass) {
 		return this.defaultConversionService.convert(this.integrationProperties.getProperty(key), tClass);
 	}
 
+	@SuppressWarnings("unchecked")
+	protected <T> T extractTypeIfPossible(Object targetObject, Class<T> expectedType) {
+		if (targetObject == null) {
+			return null;
+		}
+		if (expectedType.isAssignableFrom(targetObject.getClass())) {
+			return (T) targetObject;
+		}
+		if (targetObject instanceof Advised) {
+			TargetSource targetSource = ((Advised) targetObject).getTargetSource();
+			if (targetSource == null) {
+				return null;
+			}
+			try {
+				return extractTypeIfPossible(targetSource.getTarget(), expectedType);
+			} catch (Exception e) {
+				throw new IllegalStateException(e);
+			}
+		}
+		return null;
+	}
+
 	@Override
 	public String toString() {
 		return (this.beanName != null) ? this.beanName : super.toString();