Add AbstractReactiveWebInitializer

This commit introduces a new AbstractReactiveWebInitializer in
spring-web that relies on WebHttpHandlerBuilder to detect request
processing infrastructure beans from an ApplicationContext.

This eliminates the need to create a DispatcherHandler, since it is
expected to be a Spring bean, and as a result the initializers in
spring-webflux have been deprecated.

Issue: SPR-16144

Author: rstoyanchev

spring-web/src/main/java/org/springframework/web/server/adapter/AbstractReactiveWebInitializer.java

@@ -0,0 +1,96 @@
+/*
+ * Copyright 2002-2017 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.web.server.adapter;
+
+import javax.servlet.ServletContext;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRegistration;
+
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.http.server.reactive.HttpHandler;
+import org.springframework.http.server.reactive.ServletHttpHandlerAdapter;
+import org.springframework.util.Assert;
+import org.springframework.web.WebApplicationInitializer;
+
+/**
+ * Base class for a {@link org.springframework.web.WebApplicationInitializer}
+ * that installs a Spring Reactive Web Application on a Servlet container.
+ *
+ * <p>Spring configuration is loaded and given to
+ * {@link WebHttpHandlerBuilder#applicationContext WebHttpHandlerBuilder}
+ * which scans the context looking for specific beans and creates a reactive
+ * {@link HttpHandler}. The resulting handler is installed as a Servlet through
+ * the {@link ServletHttpHandlerAdapter}.
+ *
+ * @author Rossen Stoyanchev
+ * @since 5.0.2
+ */
+public abstract class AbstractReactiveWebInitializer implements WebApplicationInitializer {
+
+	/**
+	 * The default servlet name to use. See {@link #getServletName}.
+	 */
+	public static final String DEFAULT_SERVLET_NAME = "http-handler-adapter";
+
+
+	@Override
+	public void onStartup(ServletContext servletContext) throws ServletException {
+		String servletName = getServletName();
+		Assert.hasLength(servletName, "getServletName() must not return empty or null");
+
+		ApplicationContext applicationContext = createApplicationContext();
+		Assert.notNull(applicationContext, "createApplicationContext() must not return null.");
+
+		HttpHandler httpHandler = WebHttpHandlerBuilder.applicationContext(applicationContext).build();
+		ServletHttpHandlerAdapter servlet = new ServletHttpHandlerAdapter(httpHandler);
+
+		ServletRegistration.Dynamic registration = servletContext.addServlet(servletName, servlet);
+		Assert.notNull(registration, "Failed to register servlet '" + servletName + "'.");
+
+		registration.setLoadOnStartup(1);
+		registration.addMapping("/");
+		registration.setAsyncSupported(true);
+	}
+
+	/**
+	 * Return the name to use to register the {@link ServletHttpHandlerAdapter}.
+	 * <p>By default this is {@link #DEFAULT_SERVLET_NAME}.
+	 */
+	protected String getServletName() {
+		return DEFAULT_SERVLET_NAME;
+	}
+
+	/**
+	 * Return the Spring configuration that contains application beans including
+	 * the ones detected by {@link WebHttpHandlerBuilder#applicationContext}.
+	 */
+	protected ApplicationContext createApplicationContext() {
+		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
+		Class<?>[] configClasses = getConfigClasses();
+		Assert.notEmpty(configClasses, "No Spring configuration provided.");
+		return context;
+	}
+
+	/**
+	 * Specify {@link org.springframework.context.annotation.Configuration @Configuration} and/or
+	 * {@link org.springframework.stereotype.Component @Component} classes that
+	 * make up the application configuration. The config classes are given to
+	 * {@linkplain #createApplicationContext()}.
+	 */
+	protected abstract Class<?>[] getConfigClasses();
+
+}

spring-webflux/src/main/java/org/springframework/web/reactive/support/AbstractAnnotationConfigDispatcherHandlerInitializer.java

@@ -26,13 +26,12 @@
  * to register a {@code DispatcherHandler}, wrapping it in a
  * {@link ServletHttpHandlerAdapter}, and use Java-based Spring configuration.
  *
- * <p>Concrete implementations are required to implement {@link #getConfigClasses()}.
- * Further template and customization methods are provided by
- * {@link AbstractDispatcherHandlerInitializer}.
- *
  * @author Arjen Poutsma
- * @since 5.0
+ * @deprecated in favor of
+ * {@link org.springframework.web.server.adapter.AbstractReactiveWebInitializer
+ * AbstractReactiveWebInitializer}
  */
+@Deprecated
 public abstract class AbstractAnnotationConfigDispatcherHandlerInitializer
 		extends AbstractDispatcherHandlerInitializer {
 

spring-webflux/src/main/java/org/springframework/web/reactive/support/AbstractDispatcherHandlerInitializer.java

@@ -37,13 +37,13 @@
  * implementations that register a {@link DispatcherHandler} in the servlet
  * context, wrapping it in a {@link ServletHttpHandlerAdapter}.
  *
- * <p>Most applications should consider extending the Spring Java config, sub-class
- * {@link AbstractAnnotationConfigDispatcherHandlerInitializer}.
- *
  * @author Arjen Poutsma
  * @since 5.0
- * @see AbstractServletHttpHandlerAdapterInitializer
+ * @deprecated in favor of
+ * {@link org.springframework.web.server.adapter.AbstractReactiveWebInitializer
+ * AbstractReactiveWebInitializer}
  */
+@Deprecated
 public abstract class AbstractDispatcherHandlerInitializer implements WebApplicationInitializer {
 
 	/**

spring-webflux/src/main/java/org/springframework/web/reactive/support/AbstractServletHttpHandlerAdapterInitializer.java

@@ -30,13 +30,13 @@
  * implementations that register a {@link ServletHttpHandlerAdapter} in the
  * servlet context.
  *
- * <p>See {@link AbstractDispatcherHandlerInitializer} if registering a
- * {@link org.springframework.web.reactive.DispatcherHandler DispatcherHandler}.
- *
  * @author Arjen Poutsma
  * @since 5.0
- * @see AbstractDispatcherHandlerInitializer
+ * @deprecated in favor of
+ * {@link org.springframework.web.server.adapter.AbstractReactiveWebInitializer
+ * AbstractReactiveWebInitializer}
  */
+@Deprecated
 public abstract class AbstractServletHttpHandlerAdapterInitializer implements WebApplicationInitializer {
 
 	/**

src/docs/asciidoc/web/webflux.adoc

@@ -361,9 +361,9 @@ server.start();
 [NOTE]
 ====
 To deploy as a WAR to a Servlet 3.1+ container, wrap `HttpHandler` with
-`ServletHttpHandlerAdapter` and register that as a `Servlet`. Use
-{api-spring-framework}/web/reactive/support/AbstractServletHttpHandlerAdapterInitializer.html[AbstractServletHttpHandlerAdapterInitializer]
-to automate the required Servlet container configuration.
+`ServletHttpHandlerAdapter` and register that as a `Servlet`.
+This can be automated through the use of
+{api-spring-framework}/web/server/adapter/AbstractReactiveWebInitializer.html[AbstractReactiveWebInitializer].
 ====