Provide support for filter registrations

The AbstractDispatcherServletInitializer now provides support for
the registration of filters to be mapped to the DispatcherServlet.
It also sets the asyncSupported flag by default on the
DispatcherServlet and all registered filters.

Issue: SPR-9696

spring-webmvc/src/main/java/org/springframework/web/servlet/support/AbstractDispatcherServletInitializer.java

@@ -16,11 +16,19 @@
 
 package org.springframework.web.servlet.support;
 
+import java.util.EnumSet;
+
+import javax.servlet.DispatcherType;
+import javax.servlet.Filter;
+import javax.servlet.FilterRegistration;
+import javax.servlet.FilterRegistration.Dynamic;
 import javax.servlet.ServletContext;
 import javax.servlet.ServletException;
 import javax.servlet.ServletRegistration;
 
+import org.springframework.core.Conventions;
 import org.springframework.util.Assert;
+import org.springframework.util.ObjectUtils;
 import org.springframework.web.context.AbstractContextLoaderInitializer;
 import org.springframework.web.context.WebApplicationContext;
 import org.springframework.web.servlet.DispatcherServlet;
@@ -44,6 +52,7 @@ import org.springframework.web.servlet.DispatcherServlet;
  *
  * @author Arjen Poutsma
  * @author Chris Beams
+ * @author Rossen Stoyanchev
  * @since 3.2
  */
 public abstract class AbstractDispatcherServletInitializer
@@ -87,6 +96,14 @@ public abstract class AbstractDispatcherServletInitializer
 				servletContext.addServlet(servletName, dispatcherServlet);
 		registration.setLoadOnStartup(1);
 		registration.addMapping(getServletMappings());
+		registration.setAsyncSupported(isAsyncSupported());
+
+		Filter[] filters = getServletFilters();
+		if (!ObjectUtils.isEmpty(filters)) {
+			for (Filter filter : filters) {
+				registerServletFilter(servletContext, filter);
+			}
+		}
 
 		this.customizeRegistration(registration);
 	}
@@ -111,12 +128,63 @@ public abstract class AbstractDispatcherServletInitializer
 	protected abstract WebApplicationContext createServletApplicationContext();
 
 	/**
-	 * Specify the servlet mapping(s) for the {@code DispatcherServlet}, e.g. '/', '/app',
-	 * etc.
+	 * Specify the servlet mapping(s) for the {@code DispatcherServlet}, e.g. '/', '/app', etc.
 	 * @see #registerDispatcherServlet(ServletContext)
 	 */
 	protected abstract String[] getServletMappings();
 
+	/**
+	 * Specify filters to add and also map to the {@code DispatcherServlet}.
+	 *
+	 * @return an array of filters or {@code null}
+	 * @see #registerServletFilters(ServletContext, String, Filter...)
+	 */
+	protected Filter[] getServletFilters() {
+		return null;
+	}
+
+	/**
+	 * Add the given filter to the ServletContext and map it to the
+	 * {@code DispatcherServlet} as follows:
+	 * <ul>
+	 * <li>a default filter name is chosen based on its concrete type
+	 * <li>the {@code asyncSupported} flag is set depending on the
+	 * return value of {@link #isAsyncSupported() asyncSupported}
+	 * <li>a filter mapping is created with dispatcher types {@code REQUEST},
+	 * {@code FORWARD}, {@code INCLUDE}, and conditionally {@code ASYNC} depending
+	 * on the return value of {@link #isAsyncSupported() asyncSupported}
+	 * </ul>
+	 * <p>If the above defaults are not suitable or insufficient, register
+	 * filters directly with the {@code ServletContext}.
+	 *
+	 * @param servletContext the servlet context to register filters with
+	 * @param servletName the name of the servlet to map the filters to
+	 * @param filters the filters to be registered
+	 * @return the filter registration
+	 */
+	protected FilterRegistration.Dynamic registerServletFilter(ServletContext servletContext, Filter filter) {
+		String filterName = Conventions.getVariableName(filter);
+		Dynamic registration = servletContext.addFilter(filterName, filter);
+		registration.setAsyncSupported(isAsyncSupported());
+		registration.addMappingForServletNames(getDispatcherTypes(), false, getServletName());
+		return registration;
+	}
+
+	private EnumSet<DispatcherType> getDispatcherTypes() {
+		return isAsyncSupported() ?
+			EnumSet.of(DispatcherType.REQUEST, DispatcherType.FORWARD, DispatcherType.INCLUDE, DispatcherType.ASYNC) :
+			EnumSet.of(DispatcherType.REQUEST, DispatcherType.FORWARD, DispatcherType.INCLUDE);
+	}
+
+	/**
+	 * A single place to control the {@code asyncSupported} flag for the
+	 * {@code DispatcherServlet} and all filters added via {@link #getServletFilters()}.
+	 * <p>The default value is "true".
+	 */
+	protected boolean isAsyncSupported() {
+		return true;
+	}
+
 	/**
 	 * Optionally perform further registration customization once
 	 * {@link #registerDispatcherServlet(ServletContext)} has completed.