INT-3655: Remove Reactor Function Usage

JIRA: https://jira.spring.io/browse/INT-3655

In addition, change `GatewayProxyFactoryBean` to the logic to ensure that the Reactor is really `optional`

INT-3655: Doc Polishing

build.gradle

@@ -110,7 +110,7 @@ subprojects { subproject ->
 		pahoMqttClientVersion = '0.4.0'
 		postgresVersion = '9.1-901-1.jdbc4'
 		reactorVersion = '2.0.0.RC1'
-		reactorSpringVersion = '2.0.0.M2'
+		reactorSpringVersion = '2.0.0.RC1'
 		romeToolsVersion = '1.5.0'
 		saajApiVersion = '1.3.5'
 		saajImplVersion = '1.3.23'

spring-integration-core/src/main/java/org/springframework/integration/gateway/GatewayProxyFactoryBean.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -86,6 +86,9 @@ public class GatewayProxyFactoryBean extends AbstractEndpoint
 
 	private static final SpelExpressionParser PARSER = new SpelExpressionParser();
 
+	private static final boolean reactorPresent = ClassUtils.isPresent("reactor.Environment",
+			GatewayProxyFactoryBean.class.getClassLoader());
+
 	private volatile Class<?> serviceInterface;
 
 	private volatile MessageChannel defaultRequestChannel;
@@ -116,7 +119,7 @@ public class GatewayProxyFactoryBean extends AbstractEndpoint
 
 	private volatile Class<?> asyncSubmitListenableType;
 
-	private volatile Environment reactorEnvironment;
+	private volatile Object reactorEnvironment;
 
 	private volatile boolean initialized;
 
@@ -255,7 +258,10 @@ public class GatewayProxyFactoryBean extends AbstractEndpoint
 	 * @param reactorEnvironment the Reactor Environment.
 	 * @since 4.1
 	 */
-	public void setReactorEnvironment(Environment reactorEnvironment) {
+	public void setReactorEnvironment(Object reactorEnvironment) {
+		if (!Environment.class.getName().equals(reactorEnvironment.getClass().getName())) {
+			throw new IllegalArgumentException("The 'reactorEnvironment' must be instance of 'reactor.Environment'");
+		}
 		this.reactorEnvironment = reactorEnvironment;
 	}
 
@@ -354,11 +360,11 @@ public class GatewayProxyFactoryBean extends AbstractEndpoint
 				}
 			}
 		}
-		if (Promise.class.isAssignableFrom(returnType)) {
+		if (reactorPresent && Promise.class.isAssignableFrom(returnType)) {
 			if (this.reactorEnvironment == null) {
 				throw new IllegalStateException("'reactorEnvironment' is required in case of 'Promise' return type.");
 			}
-			return Promises.<Object>task(this.reactorEnvironment,
+			return Promises.<Object>task((Environment) this.reactorEnvironment,
 					Functions.supplier(new AsyncInvocationTask(invocation)));
 		}
 		return this.doInvoke(invocation);
@@ -584,7 +590,7 @@ public class GatewayProxyFactoryBean extends AbstractEndpoint
 		if (Future.class.isAssignableFrom(expectedReturnType)) {
 			return (T) source;
 		}
-		if (Promise.class.isAssignableFrom(expectedReturnType)) {
+		if (reactorPresent && Promise.class.isAssignableFrom(expectedReturnType)) {
 			return (T) source;
 		}
 		if (this.getConversionService() != null) {
@@ -596,7 +602,8 @@ public class GatewayProxyFactoryBean extends AbstractEndpoint
 	}
 
 	private static boolean hasReturnParameterizedWithMessage(Method method) {
-		if (Future.class.isAssignableFrom(method.getReturnType()) || Promise.class.isAssignableFrom(method.getReturnType())) {
+		if (Future.class.isAssignableFrom(method.getReturnType())
+				|| (reactorPresent && Promise.class.isAssignableFrom(method.getReturnType()))) {
 			Type returnType = method.getGenericReturnType();
 			if (returnType instanceof ParameterizedType) {
 				Type[] typeArgs = ((ParameterizedType) returnType).getActualTypeArguments();

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -24,12 +24,11 @@ import java.util.concurrent.atomic.AtomicInteger;
 
 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;
 
-import reactor.fn.Function;
-
 /**
  * Base class for Message-splitting handlers.
  *

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

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2015 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.
+ *
+ * <p>This is a copy of Java 8 {@code Function} interface.
+ *
+ * @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
+ * @since 4.0
+ */
+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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014 the original author or authors.
+ * Copyright 2014-2015 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.
@@ -19,8 +19,6 @@ package org.springframework.integration.util;
 import java.util.Iterator;
 import java.util.NoSuchElementException;
 
-import reactor.fn.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()}.

src/reference/docbook/whats-new.xml

@@ -94,5 +94,19 @@
 				to 1. The annotation now defaults this attribute to 1.
 			</para>
 		</section>
+		<section id="4.2-api-changes">
+			<title>API Changes</title>
+			<para>
+				<classname>o.s.integtation.util.FunctionIterator</classname> now requires a
+				<interfacename>o.s.integration.util.Function</interfacename> instead of a
+				<interfacename>reactor.function.Function</interfacename>. This was done to remove
+				an unnecessary hard dependency on Reactor. Any uses of this iterator will need to
+				change the import.
+			</para>
+			<para>
+				Of course, Reactor is still supported for functionality such as the <code>Promise</code>
+				gateway; the dependency was removed for those users who don't need it.
+			</para>
+		</section>
 	</section>
 </chapter>