Add request handling infrastructure

HandlerMapping, HandlerAdapter, HandlerResultHandler (+ HandlerResult)
as the basic request handling contracts. DispatcherHandler to drive
overall request handling.

DispatcherApp provides minimal implementations of the above contracts
enough to put together a running example that returns
200 text/plain "Hello world".

spring-web-reactive/src/main/java/org/springframework/reactive/web/DispatcherHttpHandler.java

@@ -0,0 +1,169 @@
+/*
+ * 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.
+ * 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.reactive.web;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.reactivestreams.Publisher;
+import org.reactivestreams.Subscriber;
+import org.reactivestreams.Subscription;
+
+import org.springframework.beans.factory.BeanFactoryUtils;
+import org.springframework.context.ApplicationContext;
+import org.springframework.http.HttpStatus;
+
+/**
+ * @author Rossen Stoyanchev
+ */
+public class DispatcherHttpHandler implements HttpHandler {
+
+	private List<HandlerMapping> handlerMappings;
+
+	private List<HandlerAdapter> handlerAdapters;
+
+	private List<HandlerResultHandler> resultHandlers;
+
+
+	protected void initStrategies(ApplicationContext context) {
+
+		this.handlerMappings = new ArrayList<>(BeanFactoryUtils.beansOfTypeIncludingAncestors(
+				context, HandlerMapping.class, true, false).values());
+
+		this.handlerAdapters = new ArrayList<>(BeanFactoryUtils.beansOfTypeIncludingAncestors(
+				context, HandlerAdapter.class, true, false).values());
+
+		this.resultHandlers = new ArrayList<>(BeanFactoryUtils.beansOfTypeIncludingAncestors(
+				context, HandlerResultHandler.class, true, false).values());
+	}
+
+
+	@Override
+	public Publisher<Void> handle(ServerHttpRequest request, ServerHttpResponse response) {
+
+		Object handler = getHandler(request);
+		if (handler == null) {
+			// No exception handling mechanism yet
+			response.setStatusCode(HttpStatus.NOT_FOUND);
+			return Publishers.complete();
+		}
+
+		HandlerAdapter handlerAdapter = getHandlerAdapter(handler);
+		final Publisher<HandlerResult> resultPublisher = handlerAdapter.handle(request, response, handler);
+
+		return new Publisher<Void>() {
+
+			@Override
+			public void subscribe(final Subscriber<? super Void> subscriber) {
+
+				resultPublisher.subscribe(new Subscriber<HandlerResult>() {
+
+					@Override
+					public void onSubscribe(Subscription subscription) {
+						subscription.request(Long.MAX_VALUE);
+					}
+
+					@Override
+					public void onNext(HandlerResult result) {
+						for (HandlerResultHandler resultHandler : resultHandlers) {
+							if (resultHandler.supports(result)) {
+								Publisher<Void> publisher = resultHandler.handleResult(request, response, result);
+								publisher.subscribe(new Subscriber<Void>() {
+									@Override
+									public void onSubscribe(Subscription subscription) {
+										subscription.request(Long.MAX_VALUE);
+									}
+
+									@Override
+									public void onNext(Void aVoid) {
+										// no op
+									}
+
+									@Override
+									public void onError(Throwable error) {
+										// Result handling error (no exception handling mechanism yet)
+										subscriber.onError(error);
+									}
+
+									@Override
+									public void onComplete() {
+										subscriber.onComplete();
+									}
+								});
+							}
+						}
+					}
+
+					@Override
+					public void onError(Throwable error) {
+						// Application handler error (no exception handling mechanism yet)
+						subscriber.onError(error);
+					}
+
+					@Override
+					public void onComplete() {
+						// do nothing
+					}
+				});
+			}
+		};
+	}
+
+	protected Object getHandler(ServerHttpRequest request) {
+		Object handler = null;
+		for (HandlerMapping handlerMapping : this.handlerMappings) {
+			handler = handlerMapping.getHandler(request);
+			if (handler != null) {
+				break;
+			}
+		}
+		return handler;
+	}
+
+	protected HandlerAdapter getHandlerAdapter(Object handler) {
+		for (HandlerAdapter handlerAdapter : this.handlerAdapters) {
+			if (handlerAdapter.supports(handler)) {
+				return handlerAdapter;
+			}
+		}
+		// more specific exception
+		throw new IllegalStateException("No HandlerAdapter for " + handler);
+	}
+
+
+	private static class Publishers {
+
+
+		public static Publisher<Void> complete() {
+			return subscriber -> {
+				subscriber.onSubscribe(new NoopSubscription());
+				subscriber.onComplete();
+			};
+		}
+	}
+
+	private static class NoopSubscription implements Subscription {
+
+		@Override
+		public void request(long n) {
+		}
+
+		@Override
+		public void cancel() {
+		}
+	}
+
+}

spring-web-reactive/src/main/java/org/springframework/reactive/web/HandlerAdapter.java

@@ -0,0 +1,29 @@
+/*
+ * 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.
+ * 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.reactive.web;
+
+import org.reactivestreams.Publisher;
+
+/**
+ * @author Rossen Stoyanchev
+ */
+public interface HandlerAdapter {
+
+	boolean supports(Object handler);
+
+	Publisher<HandlerResult> handle(ServerHttpRequest request, ServerHttpResponse response, Object handler);
+
+}

spring-web-reactive/src/main/java/org/springframework/reactive/web/HandlerMapping.java

@@ -0,0 +1,25 @@
+/*
+ * 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.
+ * 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.reactive.web;
+
+/**
+ * @author Rossen Stoyanchev
+ */
+public interface HandlerMapping {
+
+	Object getHandler(ServerHttpRequest request);
+
+}

spring-web-reactive/src/main/java/org/springframework/reactive/web/HandlerResult.java

@@ -0,0 +1,35 @@
+/*
+ * 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.
+ * 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.reactive.web;
+
+/**
+ * @author Rossen Stoyanchev
+ */
+public class HandlerResult {
+
+	private final Object returnValue;
+
+
+	public HandlerResult(Object returnValue) {
+		this.returnValue = returnValue;
+	}
+
+
+	public Object getReturnValue() {
+		return this.returnValue;
+	}
+
+}

spring-web-reactive/src/main/java/org/springframework/reactive/web/HandlerResultHandler.java

@@ -0,0 +1,29 @@
+/*
+ * 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.
+ * 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.reactive.web;
+
+import org.reactivestreams.Publisher;
+
+/**
+ * @author Rossen Stoyanchev
+ */
+public interface HandlerResultHandler {
+
+	boolean supports(HandlerResult result);
+
+	Publisher<Void> handleResult(ServerHttpRequest request, ServerHttpResponse response, HandlerResult result);
+
+}