* Check this.discardChannel first

* `Assert.state()` in `doInit()` for mutual exclusiveness

Author: artembilan

spring-integration-core/src/main/java/org/springframework/integration/splitter/AbstractMessageSplitter.java

@@ -96,14 +96,22 @@ public void setDiscardChannelName(String discardChannelName) {
 
 	@Override
 	public MessageChannel getDiscardChannel() {
-		String channelName = this.discardChannelName;
-		if (channelName != null) {
-			this.discardChannel = getChannelResolver().resolveDestination(channelName);
-			this.discardChannelName = null;
+		if (this.discardChannel == null) {
+			String channelName = this.discardChannelName;
+			if (channelName != null) {
+				this.discardChannel = getChannelResolver().resolveDestination(channelName);
+				this.discardChannelName = null;
+			}
 		}
 		return this.discardChannel;
 	}
 
+	@Override
+	protected void doInit() {
+		Assert.state(!(this.discardChannelName != null && this.discardChannel != null),
+				"'discardChannelName' and 'discardChannel' are mutually exclusive.");
+	}
+
 	@Override
 	@SuppressWarnings("unchecked")
 	protected final Object handleRequestMessage(Message<?> message) {