Make ErrorPageRegistry first class concern

Create ErrorPageRegistry and ErrorPageRegistrar interfaces that allow
error page registration to be a first class concern.

Prior to this commit ErrorPageFilter needed to implement
ConfigurableEmbeddedServletContainer in order to receive ErrorPage
registrations.

Closes gh-5789

spring-boot/src/main/java/org/springframework/boot/context/embedded/ConfigurableEmbeddedServletContainer.java

@@ -23,6 +23,7 @@ import java.util.Set;
 import java.util.concurrent.TimeUnit;
 
 import org.springframework.boot.web.servlet.ErrorPage;
+import org.springframework.boot.web.servlet.ErrorPageRegistry;
 import org.springframework.boot.web.servlet.ServletContextInitializer;
 
 /**
@@ -36,7 +37,7 @@ import org.springframework.boot.web.servlet.ServletContextInitializer;
  * @see EmbeddedServletContainerFactory
  * @see EmbeddedServletContainerCustomizer
  */
-public interface ConfigurableEmbeddedServletContainer {
+public interface ConfigurableEmbeddedServletContainer extends ErrorPageRegistry {
 
 	/**
 	 * Sets the context path for the embedded servlet container. The context should start
@@ -102,12 +103,6 @@ public interface ConfigurableEmbeddedServletContainer {
 	 */
 	void setRegisterDefaultServlet(boolean registerDefaultServlet);
 
-	/**
-	 * Adds error pages that will be used when handling exceptions.
-	 * @param errorPages the error pages
-	 */
-	void addErrorPages(ErrorPage... errorPages);
-
 	/**
 	 * Sets the error pages that will be used when handling exceptions.
 	 * @param errorPages the error pages

spring-boot/src/main/java/org/springframework/boot/context/web/ErrorPageFilter.java

@@ -18,8 +18,8 @@ package org.springframework.boot.context.web;
 
 import javax.servlet.Filter;
 
-import org.springframework.boot.context.embedded.ErrorPageRegistrar;
-import org.springframework.boot.context.embedded.ErrorPageRegistry;
+import org.springframework.boot.web.servlet.ErrorPageRegistrar;
+import org.springframework.boot.web.servlet.ErrorPageRegistry;
 import org.springframework.core.Ordered;
 import org.springframework.core.annotation.Order;
 import org.springframework.stereotype.Component;

spring-boot/src/main/java/org/springframework/boot/context/web/NonEmbeddedServletContainerFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2013 the original author or authors.
+ * Copyright 2012-2016 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.
@@ -17,13 +17,16 @@
 package org.springframework.boot.context.web;
 
 import org.springframework.boot.context.embedded.EmbeddedServletContainerFactory;
+import org.springframework.boot.web.servlet.ErrorPageRegistry;
 
 /**
  * Marker interface for {@link EmbeddedServletContainerFactory} types that are actually
  * safe to run in a non-embedded container.
  *
  * @author Dave Syer
+ * @deprecated as of 1.4 in favor of {@link ErrorPageRegistry}
  */
+@Deprecated
 public interface NonEmbeddedServletContainerFactory {
 
 }

spring-boot/src/main/java/org/springframework/boot/web/servlet/ErrorPageRegistrar.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2012-2016 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.boot.web.servlet;
+
+/**
+ * Interface to be implemented by types that register {@link ErrorPage ErrorPages}.
+ *
+ * @author Phillip Webb
+ * @since 1.4.0
+ */
+public interface ErrorPageRegistrar {
+
+	/**
+	 * Register pages as required with the given registry.
+	 * @param registry the error page registry
+	 */
+	void registerErrorPages(ErrorPageRegistry registry);
+
+}

spring-boot/src/main/java/org/springframework/boot/web/servlet/ErrorPageRegistrarBeanPostProcessor.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2012-2016 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.boot.web.servlet;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.config.BeanPostProcessor;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.ApplicationContextAware;
+import org.springframework.core.annotation.AnnotationAwareOrderComparator;
+
+/**
+ * {@link BeanPostProcessor} that apply all {@link ErrorPageRegistrar}s from the bean
+ * factory to {@link ErrorPageRegistry} beans.
+ *
+ * @author Phillip Webb
+ * @since 1.4.0
+ */
+public class ErrorPageRegistrarBeanPostProcessor
+		implements BeanPostProcessor, ApplicationContextAware {
+
+	private ApplicationContext applicationContext;
+
+	private List<ErrorPageRegistrar> registrars;
+
+	@Override
+	public void setApplicationContext(ApplicationContext applicationContext)
+			throws BeansException {
+		this.applicationContext = applicationContext;
+	}
+
+	@Override
+	public Object postProcessBeforeInitialization(Object bean, String beanName)
+			throws BeansException {
+		if (bean instanceof ErrorPageRegistry) {
+			postProcessBeforeInitialization((ErrorPageRegistry) bean);
+		}
+		return bean;
+	}
+
+	@Override
+	public Object postProcessAfterInitialization(Object bean, String beanName)
+			throws BeansException {
+		return bean;
+	}
+
+	private void postProcessBeforeInitialization(ErrorPageRegistry registry) {
+		for (ErrorPageRegistrar registrar : getRegistrars()) {
+			registrar.registerErrorPages(registry);
+		}
+	}
+
+	private Collection<ErrorPageRegistrar> getRegistrars() {
+		if (this.registrars == null) {
+			// Look up does not include the parent context
+			this.registrars = new ArrayList<ErrorPageRegistrar>(this.applicationContext
+					.getBeansOfType(ErrorPageRegistrar.class, false, false).values());
+			Collections.sort(this.registrars, AnnotationAwareOrderComparator.INSTANCE);
+			this.registrars = Collections.unmodifiableList(this.registrars);
+		}
+		return this.registrars;
+	}
+
+}

spring-boot/src/main/java/org/springframework/boot/web/servlet/ErrorPageRegistry.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2012-2016 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.boot.web.servlet;
+
+/**
+ * Interface for a registry that holds {@link ErrorPage ErrorPages}.
+ *
+ * @author Phillip Webb
+ * @since 1.4.0
+ */
+public interface ErrorPageRegistry {
+
+	/**
+	 * Adds error pages that will be used when handling exceptions.
+	 * @param errorPages the error pages
+	 */
+	void addErrorPages(ErrorPage... errorPages);
+
+}

spring-boot/src/main/java/org/springframework/boot/web/support/ErrorPageFilter.java

@@ -33,10 +33,9 @@ import javax.servlet.http.HttpServletResponseWrapper;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
-import org.springframework.boot.context.embedded.AbstractConfigurableEmbeddedServletContainer;
-import org.springframework.boot.context.embedded.EmbeddedServletContainerCustomizer;
-import org.springframework.boot.context.web.NonEmbeddedServletContainerFactory;
 import org.springframework.boot.web.servlet.ErrorPage;
+import org.springframework.boot.web.servlet.ErrorPageRegistrar;
+import org.springframework.boot.web.servlet.ErrorPageRegistry;
 import org.springframework.core.Ordered;
 import org.springframework.core.annotation.Order;
 import org.springframework.stereotype.Component;
@@ -44,14 +43,13 @@ import org.springframework.web.filter.OncePerRequestFilter;
 import org.springframework.web.util.NestedServletException;
 
 /**
- * A special {@link AbstractConfigurableEmbeddedServletContainer} for non-embedded
+ * A Servlet {@link Filter} that provides an {@link ErrorPageRegistry} for non-embedded
  * applications (i.e. deployed WAR files). It registers error pages and handles
  * application errors by filtering requests and forwarding to the error pages instead of
  * letting the container handle them. Error pages are a feature of the servlet spec but
  * there is no Java API for registering them in the spec. This filter works around that by
- * accepting error page registrations from Spring Boot's
- * {@link EmbeddedServletContainerCustomizer} (any beans of that type in the context will
- * be applied to this container).
+ * accepting error page registrations from Spring Boot's {@link ErrorPageRegistrar} (any
+ * beans of that type in the context will be applied to this container).
  *
  * @author Dave Syer
  * @author Phillip Webb
@@ -60,8 +58,7 @@ import org.springframework.web.util.NestedServletException;
  */
 @Component
 @Order(Ordered.HIGHEST_PRECEDENCE)
-public class ErrorPageFilter extends AbstractConfigurableEmbeddedServletContainer
-		implements Filter, NonEmbeddedServletContainerFactory {
+public class ErrorPageFilter implements Filter, ErrorPageRegistry {
 
 	private static final Log logger = LogFactory.getLog(ErrorPageFilter.class);