INT-651 Use Local 'Function' Interface

Avoid adding a new dependency after backport.

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

@@ -22,10 +22,9 @@ import java.util.Collections;
 import java.util.Iterator;
 import java.util.concurrent.atomic.AtomicInteger;
 
-import reactor.function.Function;
-
 import org.springframework.integration.handler.AbstractReplyProducingMessageHandler;
 import org.springframework.integration.support.AbstractIntegrationMessageBuilder;
+import org.springframework.integration.util.Function;
 import org.springframework.integration.util.FunctionIterator;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageHeaders;
@@ -50,7 +49,7 @@ public abstract class AbstractMessageSplitter extends AbstractReplyProducingMess
 	}
 
 	@Override
-	@SuppressWarnings("unchecked")
+	@SuppressWarnings({ "unchecked", "deprecation" })
 	protected final Object handleRequestMessage(Message<?> message) {
 		Object result = this.splitMessage(message);
 		// return null if 'null'

spring-integration-core/src/main/java/org/springframework/integration/util/Function.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2014 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.integration.util;
+/**
+ * Implementations of this class perform work on the given parameter and return a result of an optionally different
+ * type.
+ *
+ * @param <T> The type of the input to the apply operation
+ * @param <R> The type of the result of the apply operation
+ *
+ * @author Jon Brisbin
+ * @author Stephane Maldini
+ * @deprecated Use {@code reactor.Function}
+ */
+@Deprecated
+public interface Function<T, R> {
+
+	/**
+	 * Execute the logic of the action, accepting the given parameter.
+	 *
+	 * @param t The parameter to pass to the action.
+	 *
+	 * @return result
+	 */
+	R apply(T t);
+
+}

spring-integration-core/src/main/java/org/springframework/integration/util/FunctionIterator.java

@@ -19,8 +19,6 @@ package org.springframework.integration.util;
 import java.util.Iterator;
 import java.util.NoSuchElementException;
 
-import reactor.function.Function;
-
 /**
  * An {@link Iterator} implementation to convert each item from the target
  * {@link #iterator} to a new object applying the {@link #function} on {@link #next()}.