/*
 * Copyright 2002-2018 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.servlet;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
import java.util.stream.Collectors;
import javax.servlet.DispatcherType;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.beans.factory.BeanFactoryUtils;
import org.springframework.beans.factory.BeanInitializationException;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.i18n.LocaleContext;
import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.support.PropertiesLoaderUtils;
import org.springframework.core.log.LogFormatUtils;
import org.springframework.http.server.ServletServerHttpRequest;
import org.springframework.lang.Nullable;
import org.springframework.ui.context.ThemeSource;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.request.ServletWebRequest;
import org.springframework.web.context.request.async.WebAsyncManager;
import org.springframework.web.context.request.async.WebAsyncUtils;
import org.springframework.web.multipart.MultipartException;
import org.springframework.web.multipart.MultipartHttpServletRequest;
import org.springframework.web.multipart.MultipartResolver;
import org.springframework.web.util.NestedServletException;
import org.springframework.web.util.WebUtils;

Central dispatcher for HTTP request handlers/controllers, e.g. for web UI controllers
or HTTP-based remote service exporters. Dispatches to registered handlers for processing
a web request, providing convenient mapping and exception handling facilities.
This servlet is very flexible: It can be used with just about any workflow, with the
installation of the appropriate adapter classes. It offers the following functionality
that distinguishes it from other request-driven web MVC frameworks:

It is based around a JavaBeans configuration mechanism.
It can use any HandlerMapping implementation - pre-built or provided as part of an application - to control the routing of requests to handler objects. Default is BeanNameUrlHandlerMapping and RequestMappingHandlerMapping. HandlerMapping objects can be defined as beans in the servlet's application context, implementing the HandlerMapping interface, overriding the default HandlerMapping if present. HandlerMappings can be given any bean name (they are tested by type). 
It can use any HandlerAdapter; this allows for using any handler interface. Default adapters are HttpRequestHandlerAdapter, SimpleControllerHandlerAdapter, for Spring's HttpRequestHandler and Controller interfaces, respectively. A default RequestMappingHandlerAdapter will be registered as well. HandlerAdapter objects can be added as beans in the application context, overriding the default HandlerAdapters. Like HandlerMappings, HandlerAdapters can be given any bean name (they are tested by type). 
The dispatcher's exception resolution strategy can be specified via a HandlerExceptionResolver, for example mapping certain exceptions to error pages. Default are ExceptionHandlerExceptionResolver, ResponseStatusExceptionResolver, and DefaultHandlerExceptionResolver. These HandlerExceptionResolvers can be overridden through the application context. HandlerExceptionResolver can be given any bean name (they are tested by type). 
Its view resolution strategy can be specified via a ViewResolver implementation, resolving symbolic view names into View objects. Default is InternalResourceViewResolver. ViewResolver objects can be added as beans in the application context, overriding the default ViewResolver. ViewResolvers can be given any bean name (they are tested by type). 
If a View or view name is not supplied by the user, then the configured RequestToViewNameTranslator will translate the current request into a view name. The corresponding bean name is "viewNameTranslator"; the default is DefaultRequestToViewNameTranslator. 
The dispatcher's strategy for resolving multipart requests is determined by a MultipartResolver implementation. Implementations for Apache Commons FileUpload and Servlet 3 are included; the typical choice is CommonsMultipartResolver. The MultipartResolver bean name is "multipartResolver"; default is none. 
Its locale resolution strategy is determined by a LocaleResolver. Out-of-the-box implementations work via HTTP accept header, cookie, or session. The LocaleResolver bean name is "localeResolver"; default is AcceptHeaderLocaleResolver. 
Its theme resolution strategy is determined by a ThemeResolver. Implementations for a fixed theme and for cookie and session storage are included. The ThemeResolver bean name is "themeResolver"; default is FixedThemeResolver. 
NOTE: The @RequestMapping annotation will only be processed if a corresponding HandlerMapping (for type-level annotations) and/or HandlerAdapter (for method-level annotations) is present in the dispatcher. This is the case by default. However, if you are defining custom HandlerMappings or HandlerAdapters, then you need to make sure that a corresponding custom RequestMappingHandlerMapping and/or RequestMappingHandlerAdapter is defined as well - provided that you intend to use @RequestMapping. 
A web application can define any number of DispatcherServlets. Each servlet will operate in its own namespace, loading its own application context with mappings, handlers, etc. Only the root application context as loaded by ContextLoaderListener, if any, will be shared. 
As of Spring 3.1, DispatcherServlet may now be injected with a web application context, rather than creating its own internally. This is useful in Servlet 3.0+ environments, which support programmatic registration of servlet instances. See the DispatcherServlet(WebApplicationContext) javadoc for details. 
Author:
Rod Johnson, Juergen Hoeller, Rob Harrop, Chris Beams, Rossen Stoyanchev
See Also:
HttpRequestHandler
Controller
ContextLoaderListener/**
 * Central dispatcher for HTTP request handlers/controllers, e.g. for web UI controllers
 * or HTTP-based remote service exporters. Dispatches to registered handlers for processing
 * a web request, providing convenient mapping and exception handling facilities.
 *
 * <p>This servlet is very flexible: It can be used with just about any workflow, with the
 * installation of the appropriate adapter classes. It offers the following functionality
 * that distinguishes it from other request-driven web MVC frameworks:
 *
 * <ul>
 * <li>It is based around a JavaBeans configuration mechanism.
 *
 * <li>It can use any {@link HandlerMapping} implementation - pre-built or provided as part
 * of an application - to control the routing of requests to handler objects. Default is
 * {@link org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping} and
 * {@link org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping}.
 * HandlerMapping objects can be defined as beans in the servlet's application context,
 * implementing the HandlerMapping interface, overriding the default HandlerMapping if
 * present. HandlerMappings can be given any bean name (they are tested by type).
 *
 * <li>It can use any {@link HandlerAdapter}; this allows for using any handler interface.
 * Default adapters are {@link org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter},
 * {@link org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter}, for Spring's
 * {@link org.springframework.web.HttpRequestHandler} and
 * {@link org.springframework.web.servlet.mvc.Controller} interfaces, respectively. A default
 * {@link org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter}
 * will be registered as well. HandlerAdapter objects can be added as beans in the
 * application context, overriding the default HandlerAdapters. Like HandlerMappings,
 * HandlerAdapters can be given any bean name (they are tested by type).
 *
 * <li>The dispatcher's exception resolution strategy can be specified via a
 * {@link HandlerExceptionResolver}, for example mapping certain exceptions to error pages.
 * Default are
 * {@link org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver},
 * {@link org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver}, and
 * {@link org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver}.
 * These HandlerExceptionResolvers can be overridden through the application context.
 * HandlerExceptionResolver can be given any bean name (they are tested by type).
 *
 * <li>Its view resolution strategy can be specified via a {@link ViewResolver}
 * implementation, resolving symbolic view names into View objects. Default is
 * {@link org.springframework.web.servlet.view.InternalResourceViewResolver}.
 * ViewResolver objects can be added as beans in the application context, overriding the
 * default ViewResolver. ViewResolvers can be given any bean name (they are tested by type).
 *
 * <li>If a {@link View} or view name is not supplied by the user, then the configured
 * {@link RequestToViewNameTranslator} will translate the current request into a view name.
 * The corresponding bean name is "viewNameTranslator"; the default is
 * {@link org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator}.
 *
 * <li>The dispatcher's strategy for resolving multipart requests is determined by a
 * {@link org.springframework.web.multipart.MultipartResolver} implementation.
 * Implementations for Apache Commons FileUpload and Servlet 3 are included; the typical
 * choice is {@link org.springframework.web.multipart.commons.CommonsMultipartResolver}.
 * The MultipartResolver bean name is "multipartResolver"; default is none.
 *
 * <li>Its locale resolution strategy is determined by a {@link LocaleResolver}.
 * Out-of-the-box implementations work via HTTP accept header, cookie, or session.
 * The LocaleResolver bean name is "localeResolver"; default is
 * {@link org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver}.
 *
 * <li>Its theme resolution strategy is determined by a {@link ThemeResolver}.
 * Implementations for a fixed theme and for cookie and session storage are included.
 * The ThemeResolver bean name is "themeResolver"; default is
 * {@link org.springframework.web.servlet.theme.FixedThemeResolver}.
 * </ul>
 *
 * <p><b>NOTE: The {@code @RequestMapping} annotation will only be processed if a
 * corresponding {@code HandlerMapping} (for type-level annotations) and/or
 * {@code HandlerAdapter} (for method-level annotations) is present in the dispatcher.</b>
 * This is the case by default. However, if you are defining custom {@code HandlerMappings}
 * or {@code HandlerAdapters}, then you need to make sure that a corresponding custom
 * {@code RequestMappingHandlerMapping} and/or {@code RequestMappingHandlerAdapter}
 * is defined as well - provided that you intend to use {@code @RequestMapping}.
 *
 * <p><b>A web application can define any number of DispatcherServlets.</b>
 * Each servlet will operate in its own namespace, loading its own application context
 * with mappings, handlers, etc. Only the root application context as loaded by
 * {@link org.springframework.web.context.ContextLoaderListener}, if any, will be shared.
 *
 * <p>As of Spring 3.1, {@code DispatcherServlet} may now be injected with a web
 * application context, rather than creating its own internally. This is useful in Servlet
 * 3.0+ environments, which support programmatic registration of servlet instances.
 * See the {@link #DispatcherServlet(WebApplicationContext)} javadoc for details.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @author Chris Beams
 * @author Rossen Stoyanchev
 * @see org.springframework.web.HttpRequestHandler
 * @see org.springframework.web.servlet.mvc.Controller
 * @see org.springframework.web.context.ContextLoaderListener
 */
@SuppressWarnings("serial")
public class DispatcherServlet extends FrameworkServlet {

	
Well-known name for the MultipartResolver object in the bean factory for this namespace. /** Well-known name for the MultipartResolver object in the bean factory for this namespace. */
	public static final String MULTIPART_RESOLVER_BEAN_NAME = "multipartResolver";

	
Well-known name for the LocaleResolver object in the bean factory for this namespace. /** Well-known name for the LocaleResolver object in the bean factory for this namespace. */
	public static final String LOCALE_RESOLVER_BEAN_NAME = "localeResolver";

	
Well-known name for the ThemeResolver object in the bean factory for this namespace. /** Well-known name for the ThemeResolver object in the bean factory for this namespace. */
	public static final String THEME_RESOLVER_BEAN_NAME = "themeResolver";

	
Well-known name for the HandlerMapping object in the bean factory for this namespace.
Only used when "detectAllHandlerMappings" is turned off.
See Also:
setDetectAllHandlerMappings/**
	 * Well-known name for the HandlerMapping object in the bean factory for this namespace.
	 * Only used when "detectAllHandlerMappings" is turned off.
	 * @see #setDetectAllHandlerMappings
	 */
	public static final String HANDLER_MAPPING_BEAN_NAME = "handlerMapping";

	
Well-known name for the HandlerAdapter object in the bean factory for this namespace.
Only used when "detectAllHandlerAdapters" is turned off.
See Also:
setDetectAllHandlerAdapters/**
	 * Well-known name for the HandlerAdapter object in the bean factory for this namespace.
	 * Only used when "detectAllHandlerAdapters" is turned off.
	 * @see #setDetectAllHandlerAdapters
	 */
	public static final String HANDLER_ADAPTER_BEAN_NAME = "handlerAdapter";

	
Well-known name for the HandlerExceptionResolver object in the bean factory for this namespace.
Only used when "detectAllHandlerExceptionResolvers" is turned off.
See Also:
setDetectAllHandlerExceptionResolvers/**
	 * Well-known name for the HandlerExceptionResolver object in the bean factory for this namespace.
	 * Only used when "detectAllHandlerExceptionResolvers" is turned off.
	 * @see #setDetectAllHandlerExceptionResolvers
	 */
	public static final String HANDLER_EXCEPTION_RESOLVER_BEAN_NAME = "handlerExceptionResolver";

	
Well-known name for the RequestToViewNameTranslator object in the bean factory for this namespace.
/**
	 * Well-known name for the RequestToViewNameTranslator object in the bean factory for this namespace.
	 */
	public static final String REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME = "viewNameTranslator";

	
Well-known name for the ViewResolver object in the bean factory for this namespace.
Only used when "detectAllViewResolvers" is turned off.
See Also:
setDetectAllViewResolvers/**
	 * Well-known name for the ViewResolver object in the bean factory for this namespace.
	 * Only used when "detectAllViewResolvers" is turned off.
	 * @see #setDetectAllViewResolvers
	 */
	public static final String VIEW_RESOLVER_BEAN_NAME = "viewResolver";

	
Well-known name for the FlashMapManager object in the bean factory for this namespace.
/**
	 * Well-known name for the FlashMapManager object in the bean factory for this namespace.
	 */
	public static final String FLASH_MAP_MANAGER_BEAN_NAME = "flashMapManager";

	
Request attribute to hold the current web application context.
Otherwise only the global web app context is obtainable by tags etc.
See Also:
findWebApplicationContext.findWebApplicationContext/**
	 * Request attribute to hold the current web application context.
	 * Otherwise only the global web app context is obtainable by tags etc.
	 * @see org.springframework.web.servlet.support.RequestContextUtils#findWebApplicationContext
	 */
	public static final String WEB_APPLICATION_CONTEXT_ATTRIBUTE = DispatcherServlet.class.getName() + ".CONTEXT";

	
Request attribute to hold the current LocaleResolver, retrievable by views.
See Also:
getLocaleResolver.getLocaleResolver/**
	 * Request attribute to hold the current LocaleResolver, retrievable by views.
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getLocaleResolver
	 */
	public static final String LOCALE_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() + ".LOCALE_RESOLVER";

	
Request attribute to hold the current ThemeResolver, retrievable by views.
See Also:
getThemeResolver.getThemeResolver/**
	 * Request attribute to hold the current ThemeResolver, retrievable by views.
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getThemeResolver
	 */
	public static final String THEME_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() + ".THEME_RESOLVER";

	
Request attribute to hold the current ThemeSource, retrievable by views.
See Also:
getThemeSource.getThemeSource/**
	 * Request attribute to hold the current ThemeSource, retrievable by views.
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getThemeSource
	 */
	public static final String THEME_SOURCE_ATTRIBUTE = DispatcherServlet.class.getName() + ".THEME_SOURCE";

	
Name of request attribute that holds a read-only Map<String,?> with "input" flash attributes saved by a previous request, if any. 
See Also:
RequestContextUtils.getInputFlashMap(HttpServletRequest)/**
	 * Name of request attribute that holds a read-only {@code Map<String,?>}
	 * with "input" flash attributes saved by a previous request, if any.
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getInputFlashMap(HttpServletRequest)
	 */
	public static final String INPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() + ".INPUT_FLASH_MAP";

	
Name of request attribute that holds the "output" FlashMap with attributes to save for a subsequent request. 
See Also:
RequestContextUtils.getOutputFlashMap(HttpServletRequest)/**
	 * Name of request attribute that holds the "output" {@link FlashMap} with
	 * attributes to save for a subsequent request.
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getOutputFlashMap(HttpServletRequest)
	 */
	public static final String OUTPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() + ".OUTPUT_FLASH_MAP";

	
Name of request attribute that holds the FlashMapManager. 
See Also:
RequestContextUtils.getFlashMapManager(HttpServletRequest)/**
	 * Name of request attribute that holds the {@link FlashMapManager}.
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getFlashMapManager(HttpServletRequest)
	 */
	public static final String FLASH_MAP_MANAGER_ATTRIBUTE = DispatcherServlet.class.getName() + ".FLASH_MAP_MANAGER";

	
Name of request attribute that exposes an Exception resolved with an HandlerExceptionResolver but where no view was rendered (e.g. setting the status code). /**
	 * Name of request attribute that exposes an Exception resolved with an
	 * {@link HandlerExceptionResolver} but where no view was rendered
	 * (e.g. setting the status code).
	 */
	public static final String EXCEPTION_ATTRIBUTE = DispatcherServlet.class.getName() + ".EXCEPTION";

	
Log category to use when no mapped handler is found for a request. /** Log category to use when no mapped handler is found for a request. */
	public static final String PAGE_NOT_FOUND_LOG_CATEGORY = "org.springframework.web.servlet.PageNotFound";

	
Name of the class path resource (relative to the DispatcherServlet class)
that defines DispatcherServlet's default strategy names.
/**
	 * Name of the class path resource (relative to the DispatcherServlet class)
	 * that defines DispatcherServlet's default strategy names.
	 */
	private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";

	
Common prefix that DispatcherServlet's default strategy attributes start with.
/**
	 * Common prefix that DispatcherServlet's default strategy attributes start with.
	 */
	private static final String DEFAULT_STRATEGIES_PREFIX = "org.springframework.web.servlet";

	
Additional logger to use when no mapped handler is found for a request. /** Additional logger to use when no mapped handler is found for a request. */
	protected static final Log pageNotFoundLogger = LogFactory.getLog(PAGE_NOT_FOUND_LOG_CATEGORY);

	private static final Properties defaultStrategies;

	static {
		// Load default strategy implementations from properties file.
		// This is currently strictly internal and not meant to be customized
		// by application developers.
		try {
			ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
			defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
		}
		catch (IOException ex) {
			throw new IllegalStateException("Could not load '" + DEFAULT_STRATEGIES_PATH + "': " + ex.getMessage());
		}
	}

	
Detect all HandlerMappings or just expect "handlerMapping" bean?. /** Detect all HandlerMappings or just expect "handlerMapping" bean?. */
	private boolean detectAllHandlerMappings = true;

	
Detect all HandlerAdapters or just expect "handlerAdapter" bean?. /** Detect all HandlerAdapters or just expect "handlerAdapter" bean?. */
	private boolean detectAllHandlerAdapters = true;

	
Detect all HandlerExceptionResolvers or just expect "handlerExceptionResolver" bean?. /** Detect all HandlerExceptionResolvers or just expect "handlerExceptionResolver" bean?. */
	private boolean detectAllHandlerExceptionResolvers = true;

	
Detect all ViewResolvers or just expect "viewResolver" bean?. /** Detect all ViewResolvers or just expect "viewResolver" bean?. */
	private boolean detectAllViewResolvers = true;

	
Throw a NoHandlerFoundException if no Handler was found to process this request? *./** Throw a NoHandlerFoundException if no Handler was found to process this request? *.*/
	private boolean throwExceptionIfNoHandlerFound = false;

	
Perform cleanup of request attributes after include request?. /** Perform cleanup of request attributes after include request?. */
	private boolean cleanupAfterInclude = true;

	
MultipartResolver used by this servlet. /** MultipartResolver used by this servlet. */
	@Nullable
	private MultipartResolver multipartResolver;

	
LocaleResolver used by this servlet. /** LocaleResolver used by this servlet. */
	@Nullable
	private LocaleResolver localeResolver;

	
ThemeResolver used by this servlet. /** ThemeResolver used by this servlet. */
	@Nullable
	private ThemeResolver themeResolver;

	
List of HandlerMappings used by this servlet. /** List of HandlerMappings used by this servlet. */
	@Nullable
	private List<HandlerMapping> handlerMappings;

	
List of HandlerAdapters used by this servlet. /** List of HandlerAdapters used by this servlet. */
	@Nullable
	private List<HandlerAdapter> handlerAdapters;

	
List of HandlerExceptionResolvers used by this servlet. /** List of HandlerExceptionResolvers used by this servlet. */
	@Nullable
	private List<HandlerExceptionResolver> handlerExceptionResolvers;

	
RequestToViewNameTranslator used by this servlet. /** RequestToViewNameTranslator used by this servlet. */
	@Nullable
	private RequestToViewNameTranslator viewNameTranslator;

	
FlashMapManager used by this servlet. /** FlashMapManager used by this servlet. */
	@Nullable
	private FlashMapManager flashMapManager;

	
List of ViewResolvers used by this servlet. /** List of ViewResolvers used by this servlet. */
	@Nullable
	private List<ViewResolver> viewResolvers;


	
Create a new DispatcherServlet that will create its own internal web application context based on defaults and values provided through servlet init-params. Typically used in Servlet 2.5 or earlier environments, where the only option for servlet registration is through web.xml which requires the use of a no-arg constructor. 
Calling FrameworkServlet.setContextConfigLocation (init-param 'contextConfigLocation') will dictate which XML files will be loaded by the default XmlWebApplicationContext 
Calling FrameworkServlet.setContextClass (init-param 'contextClass') overrides the default XmlWebApplicationContext and allows for specifying an alternative class, such as AnnotationConfigWebApplicationContext. 
Calling FrameworkServlet.setContextInitializerClasses (init-param 'contextInitializerClasses') indicates which ApplicationContextInitializer classes should be used to further configure the internal application context prior to refresh(). 
See Also:
DispatcherServlet(WebApplicationContext)/**
	 * Create a new {@code DispatcherServlet} that will create its own internal web
	 * application context based on defaults and values provided through servlet
	 * init-params. Typically used in Servlet 2.5 or earlier environments, where the only
	 * option for servlet registration is through {@code web.xml} which requires the use
	 * of a no-arg constructor.
	 * <p>Calling {@link #setContextConfigLocation} (init-param 'contextConfigLocation')
	 * will dictate which XML files will be loaded by the
	 * {@linkplain #DEFAULT_CONTEXT_CLASS default XmlWebApplicationContext}
	 * <p>Calling {@link #setContextClass} (init-param 'contextClass') overrides the
	 * default {@code XmlWebApplicationContext} and allows for specifying an alternative class,
	 * such as {@code AnnotationConfigWebApplicationContext}.
	 * <p>Calling {@link #setContextInitializerClasses} (init-param 'contextInitializerClasses')
	 * indicates which {@code ApplicationContextInitializer} classes should be used to
	 * further configure the internal application context prior to refresh().
	 * @see #DispatcherServlet(WebApplicationContext)
	 */
	public DispatcherServlet() {
		super();
		setDispatchOptionsRequest(true);
	}

	
Create a new DispatcherServlet with the given web application context. This constructor is useful in Servlet 3.0+ environments where instance-based registration of servlets is possible through the ServletContext.addServlet API. 
Using this constructor indicates that the following properties / init-params
will be ignored:

FrameworkServlet.setContextClass(Class<?>) / 'contextClass'
FrameworkServlet.setContextConfigLocation(String) / 'contextConfigLocation'
FrameworkServlet.setContextAttribute(String) / 'contextAttribute'
FrameworkServlet.setNamespace(String) / 'namespace'

The given web application context may or may not yet be refreshed. If it has not
already been refreshed (the recommended approach), then the following will occur:

If the given context does not already have a parent, the root application context will be set as the parent.
If the given context has not already been assigned an id, one will be assigned to it
ServletContext and ServletConfig objects will be delegated to the application context
FrameworkServlet.postProcessWebApplicationContext will be called
Any ApplicationContextInitializers specified through the "contextInitializerClasses" init-param or through the FrameworkServlet.setContextInitializers property will be applied.
refresh() will be called if the context implements ConfigurableApplicationContext

If the context has already been refreshed, none of the above will occur, under the
assumption that the user has performed these actions (or not) per their specific
needs.
See WebApplicationInitializer for usage examples. 
Params:
webApplicationContext – the context to use
See Also:
FrameworkServlet.initWebApplicationContext
FrameworkServlet.configureAndRefreshWebApplicationContext
WebApplicationInitializer/**
	 * Create a new {@code DispatcherServlet} with the given web application context. This
	 * constructor is useful in Servlet 3.0+ environments where instance-based registration
	 * of servlets is possible through the {@link ServletContext#addServlet} API.
	 * <p>Using this constructor indicates that the following properties / init-params
	 * will be ignored:
	 * <ul>
	 * <li>{@link #setContextClass(Class)} / 'contextClass'</li>
	 * <li>{@link #setContextConfigLocation(String)} / 'contextConfigLocation'</li>
	 * <li>{@link #setContextAttribute(String)} / 'contextAttribute'</li>
	 * <li>{@link #setNamespace(String)} / 'namespace'</li>
	 * </ul>
	 * <p>The given web application context may or may not yet be {@linkplain
	 * ConfigurableApplicationContext#refresh() refreshed}. If it has <strong>not</strong>
	 * already been refreshed (the recommended approach), then the following will occur:
	 * <ul>
	 * <li>If the given context does not already have a {@linkplain
	 * ConfigurableApplicationContext#setParent parent}, the root application context
	 * will be set as the parent.</li>
	 * <li>If the given context has not already been assigned an {@linkplain
	 * ConfigurableApplicationContext#setId id}, one will be assigned to it</li>
	 * <li>{@code ServletContext} and {@code ServletConfig} objects will be delegated to
	 * the application context</li>
	 * <li>{@link #postProcessWebApplicationContext} will be called</li>
	 * <li>Any {@code ApplicationContextInitializer}s specified through the
	 * "contextInitializerClasses" init-param or through the {@link
	 * #setContextInitializers} property will be applied.</li>
	 * <li>{@link ConfigurableApplicationContext#refresh refresh()} will be called if the
	 * context implements {@link ConfigurableApplicationContext}</li>
	 * </ul>
	 * If the context has already been refreshed, none of the above will occur, under the
	 * assumption that the user has performed these actions (or not) per their specific
	 * needs.
	 * <p>See {@link org.springframework.web.WebApplicationInitializer} for usage examples.
	 * @param webApplicationContext the context to use
	 * @see #initWebApplicationContext
	 * @see #configureAndRefreshWebApplicationContext
	 * @see org.springframework.web.WebApplicationInitializer
	 */
	public DispatcherServlet(WebApplicationContext webApplicationContext) {
		super(webApplicationContext);
		setDispatchOptionsRequest(true);
	}


	
Set whether to detect all HandlerMapping beans in this servlet's context. Otherwise,
just a single bean with name "handlerMapping" will be expected.
Default is "true". Turn this off if you want this servlet to use a single
HandlerMapping, despite multiple HandlerMapping beans being defined in the context.
/**
	 * Set whether to detect all HandlerMapping beans in this servlet's context. Otherwise,
	 * just a single bean with name "handlerMapping" will be expected.
	 * <p>Default is "true". Turn this off if you want this servlet to use a single
	 * HandlerMapping, despite multiple HandlerMapping beans being defined in the context.
	 */
	public void setDetectAllHandlerMappings(boolean detectAllHandlerMappings) {
		this.detectAllHandlerMappings = detectAllHandlerMappings;
	}

	
Set whether to detect all HandlerAdapter beans in this servlet's context. Otherwise,
just a single bean with name "handlerAdapter" will be expected.
Default is "true". Turn this off if you want this servlet to use a single
HandlerAdapter, despite multiple HandlerAdapter beans being defined in the context.
/**
	 * Set whether to detect all HandlerAdapter beans in this servlet's context. Otherwise,
	 * just a single bean with name "handlerAdapter" will be expected.
	 * <p>Default is "true". Turn this off if you want this servlet to use a single
	 * HandlerAdapter, despite multiple HandlerAdapter beans being defined in the context.
	 */
	public void setDetectAllHandlerAdapters(boolean detectAllHandlerAdapters) {
		this.detectAllHandlerAdapters = detectAllHandlerAdapters;
	}

	
Set whether to detect all HandlerExceptionResolver beans in this servlet's context. Otherwise,
just a single bean with name "handlerExceptionResolver" will be expected.
Default is "true". Turn this off if you want this servlet to use a single
HandlerExceptionResolver, despite multiple HandlerExceptionResolver beans being defined in the context.
/**
	 * Set whether to detect all HandlerExceptionResolver beans in this servlet's context. Otherwise,
	 * just a single bean with name "handlerExceptionResolver" will be expected.
	 * <p>Default is "true". Turn this off if you want this servlet to use a single
	 * HandlerExceptionResolver, despite multiple HandlerExceptionResolver beans being defined in the context.
	 */
	public void setDetectAllHandlerExceptionResolvers(boolean detectAllHandlerExceptionResolvers) {
		this.detectAllHandlerExceptionResolvers = detectAllHandlerExceptionResolvers;
	}

	
Set whether to detect all ViewResolver beans in this servlet's context. Otherwise,
just a single bean with name "viewResolver" will be expected.
Default is "true". Turn this off if you want this servlet to use a single
ViewResolver, despite multiple ViewResolver beans being defined in the context.
/**
	 * Set whether to detect all ViewResolver beans in this servlet's context. Otherwise,
	 * just a single bean with name "viewResolver" will be expected.
	 * <p>Default is "true". Turn this off if you want this servlet to use a single
	 * ViewResolver, despite multiple ViewResolver beans being defined in the context.
	 */
	public void setDetectAllViewResolvers(boolean detectAllViewResolvers) {
		this.detectAllViewResolvers = detectAllViewResolvers;
	}

	
Set whether to throw a NoHandlerFoundException when no Handler was found for this request. This exception can then be caught with a HandlerExceptionResolver or an @ExceptionHandler controller method. 
Note that if DefaultServletHttpRequestHandler is used, then requests will always be forwarded to the default servlet and a NoHandlerFoundException would never be thrown in that case. 
Default is "false", meaning the DispatcherServlet sends a NOT_FOUND error through the
Servlet response.
Since:
4.0/**
	 * Set whether to throw a NoHandlerFoundException when no Handler was found for this request.
	 * This exception can then be caught with a HandlerExceptionResolver or an
	 * {@code @ExceptionHandler} controller method.
	 * <p>Note that if {@link org.springframework.web.servlet.resource.DefaultServletHttpRequestHandler}
	 * is used, then requests will always be forwarded to the default servlet and a
	 * NoHandlerFoundException would never be thrown in that case.
	 * <p>Default is "false", meaning the DispatcherServlet sends a NOT_FOUND error through the
	 * Servlet response.
	 * @since 4.0
	 */
	public void setThrowExceptionIfNoHandlerFound(boolean throwExceptionIfNoHandlerFound) {
		this.throwExceptionIfNoHandlerFound = throwExceptionIfNoHandlerFound;
	}

	
Set whether to perform cleanup of request attributes after an include request, that is,
whether to reset the original state of all request attributes after the DispatcherServlet
has processed within an include request. Otherwise, just the DispatcherServlet's own
request attributes will be reset, but not model attributes for JSPs or special attributes
set by views (for example, JSTL's).
Default is "true", which is strongly recommended. Views should not rely on request attributes
having been set by (dynamic) includes. This allows JSP views rendered by an included controller
to use any model attributes, even with the same names as in the main JSP, without causing side
effects. Only turn this off for special needs, for example to deliberately allow main JSPs to
access attributes from JSP views rendered by an included controller.
/**
	 * Set whether to perform cleanup of request attributes after an include request, that is,
	 * whether to reset the original state of all request attributes after the DispatcherServlet
	 * has processed within an include request. Otherwise, just the DispatcherServlet's own
	 * request attributes will be reset, but not model attributes for JSPs or special attributes
	 * set by views (for example, JSTL's).
	 * <p>Default is "true", which is strongly recommended. Views should not rely on request attributes
	 * having been set by (dynamic) includes. This allows JSP views rendered by an included controller
	 * to use any model attributes, even with the same names as in the main JSP, without causing side
	 * effects. Only turn this off for special needs, for example to deliberately allow main JSPs to
	 * access attributes from JSP views rendered by an included controller.
	 */
	public void setCleanupAfterInclude(boolean cleanupAfterInclude) {
		this.cleanupAfterInclude = cleanupAfterInclude;
	}


	
This implementation calls initStrategies. /**
	 * This implementation calls {@link #initStrategies}.
	 */
	@Override
	protected void onRefresh(ApplicationContext context) {
		initStrategies(context);
	}

	
Initialize the strategy objects that this servlet uses.
May be overridden in subclasses in order to initialize further strategy objects.
/**
	 * Initialize the strategy objects that this servlet uses.
	 * <p>May be overridden in subclasses in order to initialize further strategy objects.
	 */
	protected void initStrategies(ApplicationContext context) {
		initMultipartResolver(context);
		initLocaleResolver(context);
		initThemeResolver(context);
		initHandlerMappings(context);
		initHandlerAdapters(context);
		initHandlerExceptionResolvers(context);
		initRequestToViewNameTranslator(context);
		initViewResolvers(context);
		initFlashMapManager(context);
	}

	
Initialize the MultipartResolver used by this class.
If no bean is defined with the given name in the BeanFactory for this namespace,
no multipart handling is provided.
/**
	 * Initialize the MultipartResolver used by this class.
	 * <p>If no bean is defined with the given name in the BeanFactory for this namespace,
	 * no multipart handling is provided.
	 */
	private void initMultipartResolver(ApplicationContext context) {
		try {
			this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);
			if (logger.isTraceEnabled()) {
				logger.trace("Detected " + this.multipartResolver);
			}
			else if (logger.isDebugEnabled()) {
				logger.debug("Detected " + this.multipartResolver.getClass().getSimpleName());
			}
		}
		catch (NoSuchBeanDefinitionException ex) {
			// Default is no multipart resolver.
			this.multipartResolver = null;
			if (logger.isTraceEnabled()) {
				logger.trace("No MultipartResolver '" + MULTIPART_RESOLVER_BEAN_NAME + "' declared");
			}
		}
	}

	
Initialize the LocaleResolver used by this class.
If no bean is defined with the given name in the BeanFactory for this namespace,
we default to AcceptHeaderLocaleResolver.
/**
	 * Initialize the LocaleResolver used by this class.
	 * <p>If no bean is defined with the given name in the BeanFactory for this namespace,
	 * we default to AcceptHeaderLocaleResolver.
	 */
	private void initLocaleResolver(ApplicationContext context) {
		try {
			this.localeResolver = context.getBean(LOCALE_RESOLVER_BEAN_NAME, LocaleResolver.class);
			if (logger.isTraceEnabled()) {
				logger.trace("Detected " + this.localeResolver);
			}
			else if (logger.isDebugEnabled()) {
				logger.debug("Detected " + this.localeResolver.getClass().getSimpleName());
			}
		}
		catch (NoSuchBeanDefinitionException ex) {
			// We need to use the default.
			this.localeResolver = getDefaultStrategy(context, LocaleResolver.class);
			if (logger.isTraceEnabled()) {
				logger.trace("No LocaleResolver '" + LOCALE_RESOLVER_BEAN_NAME +
						"': using default [" + this.localeResolver.getClass().getSimpleName() + "]");
			}
		}
	}

	
Initialize the ThemeResolver used by this class.
If no bean is defined with the given name in the BeanFactory for this namespace,
we default to a FixedThemeResolver.
/**
	 * Initialize the ThemeResolver used by this class.
	 * <p>If no bean is defined with the given name in the BeanFactory for this namespace,
	 * we default to a FixedThemeResolver.
	 */
	private void initThemeResolver(ApplicationContext context) {
		try {
			this.themeResolver = context.getBean(THEME_RESOLVER_BEAN_NAME, ThemeResolver.class);
			if (logger.isTraceEnabled()) {
				logger.trace("Detected " + this.themeResolver);
			}
			else if (logger.isDebugEnabled()) {
				logger.debug("Detected " + this.themeResolver.getClass().getSimpleName());
			}
		}
		catch (NoSuchBeanDefinitionException ex) {
			// We need to use the default.
			this.themeResolver = getDefaultStrategy(context, ThemeResolver.class);
			if (logger.isTraceEnabled()) {
				logger.trace("No ThemeResolver '" + THEME_RESOLVER_BEAN_NAME +
						"': using default [" + this.themeResolver.getClass().getSimpleName() + "]");
			}
		}
	}

	
Initialize the HandlerMappings used by this class.
If no HandlerMapping beans are defined in the BeanFactory for this namespace,
we default to BeanNameUrlHandlerMapping.
/**
	 * Initialize the HandlerMappings used by this class.
	 * <p>If no HandlerMapping beans are defined in the BeanFactory for this namespace,
	 * we default to BeanNameUrlHandlerMapping.
	 */
	private void initHandlerMappings(ApplicationContext context) {
		this.handlerMappings = null;

		if (this.detectAllHandlerMappings) {
			// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
			Map<String, HandlerMapping> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerMappings = new ArrayList<>(matchingBeans.values());
				// We keep HandlerMappings in sorted order.
				AnnotationAwareOrderComparator.sort(this.handlerMappings);
			}
		}
		else {
			try {
				HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
				this.handlerMappings = Collections.singletonList(hm);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Ignore, we'll add a default HandlerMapping later.
			}
		}

		// Ensure we have at least one HandlerMapping, by registering
		// a default HandlerMapping if no other mappings are found.
		if (this.handlerMappings == null) {
			this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
			if (logger.isTraceEnabled()) {
				logger.trace("No HandlerMappings declared for servlet '" + getServletName() +
						"': using default strategies from DispatcherServlet.properties");
			}
		}
	}

	
Initialize the HandlerAdapters used by this class.
If no HandlerAdapter beans are defined in the BeanFactory for this namespace,
we default to SimpleControllerHandlerAdapter.
/**
	 * Initialize the HandlerAdapters used by this class.
	 * <p>If no HandlerAdapter beans are defined in the BeanFactory for this namespace,
	 * we default to SimpleControllerHandlerAdapter.
	 */
	private void initHandlerAdapters(ApplicationContext context) {
		this.handlerAdapters = null;

		if (this.detectAllHandlerAdapters) {
			// Find all HandlerAdapters in the ApplicationContext, including ancestor contexts.
			Map<String, HandlerAdapter> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerAdapters = new ArrayList<>(matchingBeans.values());
				// We keep HandlerAdapters in sorted order.
				AnnotationAwareOrderComparator.sort(this.handlerAdapters);
			}
		}
		else {
			try {
				HandlerAdapter ha = context.getBean(HANDLER_ADAPTER_BEAN_NAME, HandlerAdapter.class);
				this.handlerAdapters = Collections.singletonList(ha);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Ignore, we'll add a default HandlerAdapter later.
			}
		}

		// Ensure we have at least some HandlerAdapters, by registering
		// default HandlerAdapters if no other adapters are found.
		if (this.handlerAdapters == null) {
			this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);
			if (logger.isTraceEnabled()) {
				logger.trace("No HandlerAdapters declared for servlet '" + getServletName() +
						"': using default strategies from DispatcherServlet.properties");
			}
		}
	}

	
Initialize the HandlerExceptionResolver used by this class.
If no bean is defined with the given name in the BeanFactory for this namespace,
we default to no exception resolver.
/**
	 * Initialize the HandlerExceptionResolver used by this class.
	 * <p>If no bean is defined with the given name in the BeanFactory for this namespace,
	 * we default to no exception resolver.
	 */
	private void initHandlerExceptionResolvers(ApplicationContext context) {
		this.handlerExceptionResolvers = null;

		if (this.detectAllHandlerExceptionResolvers) {
			// Find all HandlerExceptionResolvers in the ApplicationContext, including ancestor contexts.
			Map<String, HandlerExceptionResolver> matchingBeans = BeanFactoryUtils
					.beansOfTypeIncludingAncestors(context, HandlerExceptionResolver.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerExceptionResolvers = new ArrayList<>(matchingBeans.values());
				// We keep HandlerExceptionResolvers in sorted order.
				AnnotationAwareOrderComparator.sort(this.handlerExceptionResolvers);
			}
		}
		else {
			try {
				HandlerExceptionResolver her =
						context.getBean(HANDLER_EXCEPTION_RESOLVER_BEAN_NAME, HandlerExceptionResolver.class);
				this.handlerExceptionResolvers = Collections.singletonList(her);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Ignore, no HandlerExceptionResolver is fine too.
			}
		}

		// Ensure we have at least some HandlerExceptionResolvers, by registering
		// default HandlerExceptionResolvers if no other resolvers are found.
		if (this.handlerExceptionResolvers == null) {
			this.handlerExceptionResolvers = getDefaultStrategies(context, HandlerExceptionResolver.class);
			if (logger.isTraceEnabled()) {
				logger.trace("No HandlerExceptionResolvers declared in servlet '" + getServletName() +
						"': using default strategies from DispatcherServlet.properties");
			}
		}
	}

	
Initialize the RequestToViewNameTranslator used by this servlet instance.
If no implementation is configured then we default to DefaultRequestToViewNameTranslator.
/**
	 * Initialize the RequestToViewNameTranslator used by this servlet instance.
	 * <p>If no implementation is configured then we default to DefaultRequestToViewNameTranslator.
	 */
	private void initRequestToViewNameTranslator(ApplicationContext context) {
		try {
			this.viewNameTranslator =
					context.getBean(REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME, RequestToViewNameTranslator.class);
			if (logger.isTraceEnabled()) {
				logger.trace("Detected " + this.viewNameTranslator.getClass().getSimpleName());
			}
			else if (logger.isDebugEnabled()) {
				logger.debug("Detected " + this.viewNameTranslator);
			}
		}
		catch (NoSuchBeanDefinitionException ex) {
			// We need to use the default.
			this.viewNameTranslator = getDefaultStrategy(context, RequestToViewNameTranslator.class);
			if (logger.isTraceEnabled()) {
				logger.trace("No RequestToViewNameTranslator '" + REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME +
						"': using default [" + this.viewNameTranslator.getClass().getSimpleName() + "]");
			}
		}
	}

	
Initialize the ViewResolvers used by this class.
If no ViewResolver beans are defined in the BeanFactory for this
namespace, we default to InternalResourceViewResolver.
/**
	 * Initialize the ViewResolvers used by this class.
	 * <p>If no ViewResolver beans are defined in the BeanFactory for this
	 * namespace, we default to InternalResourceViewResolver.
	 */
	private void initViewResolvers(ApplicationContext context) {
		this.viewResolvers = null;

		if (this.detectAllViewResolvers) {
			// Find all ViewResolvers in the ApplicationContext, including ancestor contexts.
			Map<String, ViewResolver> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.viewResolvers = new ArrayList<>(matchingBeans.values());
				// We keep ViewResolvers in sorted order.
				AnnotationAwareOrderComparator.sort(this.viewResolvers);
			}
		}
		else {
			try {
				ViewResolver vr = context.getBean(VIEW_RESOLVER_BEAN_NAME, ViewResolver.class);
				this.viewResolvers = Collections.singletonList(vr);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Ignore, we'll add a default ViewResolver later.
			}
		}

		// Ensure we have at least one ViewResolver, by registering
		// a default ViewResolver if no other resolvers are found.
		if (this.viewResolvers == null) {
			this.viewResolvers = getDefaultStrategies(context, ViewResolver.class);
			if (logger.isTraceEnabled()) {
				logger.trace("No ViewResolvers declared for servlet '" + getServletName() +
						"': using default strategies from DispatcherServlet.properties");
			}
		}
	}

	
Initialize the FlashMapManager used by this servlet instance. 
If no implementation is configured then we default to org.springframework.web.servlet.support.DefaultFlashMapManager. /**
	 * Initialize the {@link FlashMapManager} used by this servlet instance.
	 * <p>If no implementation is configured then we default to
	 * {@code org.springframework.web.servlet.support.DefaultFlashMapManager}.
	 */
	private void initFlashMapManager(ApplicationContext context) {
		try {
			this.flashMapManager = context.getBean(FLASH_MAP_MANAGER_BEAN_NAME, FlashMapManager.class);
			if (logger.isTraceEnabled()) {
				logger.trace("Detected " + this.flashMapManager.getClass().getSimpleName());
			}
			else if (logger.isDebugEnabled()) {
				logger.debug("Detected " + this.flashMapManager);
			}
		}
		catch (NoSuchBeanDefinitionException ex) {
			// We need to use the default.
			this.flashMapManager = getDefaultStrategy(context, FlashMapManager.class);
			if (logger.isTraceEnabled()) {
				logger.trace("No FlashMapManager '" + FLASH_MAP_MANAGER_BEAN_NAME +
						"': using default [" + this.flashMapManager.getClass().getSimpleName() + "]");
			}
		}
	}

	
Return this servlet's ThemeSource, if any; else return null. 
Default is to return the WebApplicationContext as ThemeSource,
provided that it implements the ThemeSource interface.
See Also:
FrameworkServlet.getWebApplicationContext()
Returns:
the ThemeSource, if any/**
	 * Return this servlet's ThemeSource, if any; else return {@code null}.
	 * <p>Default is to return the WebApplicationContext as ThemeSource,
	 * provided that it implements the ThemeSource interface.
	 * @return the ThemeSource, if any
	 * @see #getWebApplicationContext()
	 */
	@Nullable
	public final ThemeSource getThemeSource() {
		return (getWebApplicationContext() instanceof ThemeSource ? (ThemeSource) getWebApplicationContext() : null);
	}

	
Obtain this servlet's MultipartResolver, if any.
Returns:
the MultipartResolver used by this servlet, or null if none (indicating that no multipart support is available)/**
	 * Obtain this servlet's MultipartResolver, if any.
	 * @return the MultipartResolver used by this servlet, or {@code null} if none
	 * (indicating that no multipart support is available)
	 */
	@Nullable
	public final MultipartResolver getMultipartResolver() {
		return this.multipartResolver;
	}

	
Return the configured HandlerMapping beans that were detected by type in the WebApplicationContext or initialized based on the default set of strategies from DispatcherServlet.properties. 
Note: This method may return null if invoked prior to onRefresh(ApplicationContext). 
Returns:
an immutable list with the configured mappings, or null if not initialized yet
Since:
5.0/**
	 * Return the configured {@link HandlerMapping} beans that were detected by
	 * type in the {@link WebApplicationContext} or initialized based on the
	 * default set of strategies from {@literal DispatcherServlet.properties}.
	 * <p><strong>Note:</strong> This method may return {@code null} if invoked
	 * prior to {@link #onRefresh(ApplicationContext)}.
	 * @return an immutable list with the configured mappings, or {@code null}
	 * if not initialized yet
	 * @since 5.0
	 */
	@Nullable
	public final List<HandlerMapping> getHandlerMappings() {
		return (this.handlerMappings != null ? Collections.unmodifiableList(this.handlerMappings) : null);
	}

	
Return the default strategy object for the given strategy interface.
The default implementation delegates to getDefaultStrategies, expecting a single object in the list. 
Params:
context – the current WebApplicationContext
strategyInterface – the strategy interface
See Also:
getDefaultStrategies
Returns:
the corresponding strategy object/**
	 * Return the default strategy object for the given strategy interface.
	 * <p>The default implementation delegates to {@link #getDefaultStrategies},
	 * expecting a single object in the list.
	 * @param context the current WebApplicationContext
	 * @param strategyInterface the strategy interface
	 * @return the corresponding strategy object
	 * @see #getDefaultStrategies
	 */
	protected <T> T getDefaultStrategy(ApplicationContext context, Class<T> strategyInterface) {
		List<T> strategies = getDefaultStrategies(context, strategyInterface);
		if (strategies.size() != 1) {
			throw new BeanInitializationException(
					"DispatcherServlet needs exactly 1 strategy for interface [" + strategyInterface.getName() + "]");
		}
		return strategies.get(0);
	}

	
Create a List of default strategy objects for the given strategy interface.
The default implementation uses the "DispatcherServlet.properties" file (in the same
package as the DispatcherServlet class) to determine the class names. It instantiates
the strategy objects through the context's BeanFactory.
Params:
context – the current WebApplicationContext
strategyInterface – the strategy interface
Returns:
the List of corresponding strategy objects/**
	 * Create a List of default strategy objects for the given strategy interface.
	 * <p>The default implementation uses the "DispatcherServlet.properties" file (in the same
	 * package as the DispatcherServlet class) to determine the class names. It instantiates
	 * the strategy objects through the context's BeanFactory.
	 * @param context the current WebApplicationContext
	 * @param strategyInterface the strategy interface
	 * @return the List of corresponding strategy objects
	 */
	@SuppressWarnings("unchecked")
	protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
		String key = strategyInterface.getName();
		String value = defaultStrategies.getProperty(key);
		if (value != null) {
			String[] classNames = StringUtils.commaDelimitedListToStringArray(value);
			List<T> strategies = new ArrayList<>(classNames.length);
			for (String className : classNames) {
				try {
					Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());
					Object strategy = createDefaultStrategy(context, clazz);
					strategies.add((T) strategy);
				}
				catch (ClassNotFoundException ex) {
					throw new BeanInitializationException(
							"Could not find DispatcherServlet's default strategy class [" + className +
							"] for interface [" + key + "]", ex);
				}
				catch (LinkageError err) {
					throw new BeanInitializationException(
							"Unresolvable class definition for DispatcherServlet's default strategy class [" +
							className + "] for interface [" + key + "]", err);
				}
			}
			return strategies;
		}
		else {
			return new LinkedList<>();
		}
	}

	
Create a default strategy.
The default implementation uses AutowireCapableBeanFactory.createBean. 
Params:
context – the current WebApplicationContext
clazz – the strategy implementation class to instantiate
See Also:
ApplicationContext.getAutowireCapableBeanFactory()
AutowireCapableBeanFactory.createBean
Returns:
the fully configured strategy instance/**
	 * Create a default strategy.
	 * <p>The default implementation uses
	 * {@link org.springframework.beans.factory.config.AutowireCapableBeanFactory#createBean}.
	 * @param context the current WebApplicationContext
	 * @param clazz the strategy implementation class to instantiate
	 * @return the fully configured strategy instance
	 * @see org.springframework.context.ApplicationContext#getAutowireCapableBeanFactory()
	 * @see org.springframework.beans.factory.config.AutowireCapableBeanFactory#createBean
	 */
	protected Object createDefaultStrategy(ApplicationContext context, Class<?> clazz) {
		return context.getAutowireCapableBeanFactory().createBean(clazz);
	}


	
Exposes the DispatcherServlet-specific request attributes and delegates to doDispatch for the actual dispatching. /**
	 * Exposes the DispatcherServlet-specific request attributes and delegates to {@link #doDispatch}
	 * for the actual dispatching.
	 */
	@Override
	protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
		logRequest(request);

		// Keep a snapshot of the request attributes in case of an include,
		// to be able to restore the original attributes after the include.
		Map<String, Object> attributesSnapshot = null;
		if (WebUtils.isIncludeRequest(request)) {
			attributesSnapshot = new HashMap<>();
			Enumeration<?> attrNames = request.getAttributeNames();
			while (attrNames.hasMoreElements()) {
				String attrName = (String) attrNames.nextElement();
				if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
					attributesSnapshot.put(attrName, request.getAttribute(attrName));
				}
			}
		}

		// Make framework objects available to handlers and view objects.
		request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
		request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
		request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
		request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());

		if (this.flashMapManager != null) {
			FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
			if (inputFlashMap != null) {
				request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
			}
			request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
			request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
		}

		try {
			doDispatch(request, response);
		}
		finally {
			if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
				// Restore the original attribute snapshot, in case of an include.
				if (attributesSnapshot != null) {
					restoreAttributesAfterInclude(request, attributesSnapshot);
				}
			}
		}
	}

	private void logRequest(HttpServletRequest request) {
		LogFormatUtils.traceDebug(logger, traceOn -> {
			String params;
			if (isEnableLoggingRequestDetails()) {
				params = request.getParameterMap().entrySet().stream()
						.map(entry -> entry.getKey() + ":" + Arrays.toString(entry.getValue()))
						.collect(Collectors.joining(", "));
			}
			else {
				params = (request.getParameterMap().isEmpty() ? "" :  "masked");
			}

			String query = StringUtils.isEmpty(request.getQueryString()) ? "" : "?" + request.getQueryString();
			String dispatchType = (!request.getDispatcherType().equals(DispatcherType.REQUEST) ?
					"\"" + request.getDispatcherType().name() + "\" dispatch for " : "");
			String message = (dispatchType + request.getMethod() + " \"" + getRequestUri(request) +
					query + "\", parameters={" + params + "}");

			if (traceOn) {
				List<String> values = Collections.list(request.getHeaderNames());
				String headers = values.size() > 0 ? "masked" : "";
				if (isEnableLoggingRequestDetails()) {
					headers = values.stream().map(name -> name + ":" + Collections.list(request.getHeaders(name)))
							.collect(Collectors.joining(", "));
				}
				return message + ", headers={" + headers + "} in DispatcherServlet '" + getServletName() + "'";
			}
			else {
				return message;
			}
		});
	}

	
Process the actual dispatching to the handler.
The handler will be obtained by applying the servlet's HandlerMappings in order.
The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters
to find the first that supports the handler class.
All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers
themselves to decide which methods are acceptable.
Params:
request – current HTTP request
response – current HTTP response
Throws:
Exception – in case of any kind of processing failure/**
	 * Process the actual dispatching to the handler.
	 * <p>The handler will be obtained by applying the servlet's HandlerMappings in order.
	 * The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters
	 * to find the first that supports the handler class.
	 * <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers
	 * themselves to decide which methods are acceptable.
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @throws Exception in case of any kind of processing failure
	 */
	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HttpServletRequest processedRequest = request;
		HandlerExecutionChain mappedHandler = null;
		boolean multipartRequestParsed = false;

		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

		try {
			ModelAndView mv = null;
			Exception dispatchException = null;

			try {
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);

				// Determine handler for the current request.
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null) {
					noHandlerFound(processedRequest, response);
					return;
				}

				// Determine handler adapter for the current request.
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				// Process last-modified header, if supported by the handler.
				String method = request.getMethod();
				boolean isGet = "GET".equals(method);
				if (isGet || "HEAD".equals(method)) {
					long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
					if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
						return;
					}
				}

				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

				// Actually invoke the handler.
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				if (asyncManager.isConcurrentHandlingStarted()) {
					return;
				}

				applyDefaultViewName(processedRequest, mv);
				mappedHandler.applyPostHandle(processedRequest, response, mv);
			}
			catch (Exception ex) {
				dispatchException = ex;
			}
			catch (Throwable err) {
				// As of 4.3, we're processing Errors thrown from handler methods as well,
				// making them available for @ExceptionHandler methods and other scenarios.
				dispatchException = new NestedServletException("Handler dispatch failed", err);
			}
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
		catch (Exception ex) {
			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
		}
		catch (Throwable err) {
			triggerAfterCompletion(processedRequest, response, mappedHandler,
					new NestedServletException("Handler processing failed", err));
		}
		finally {
			if (asyncManager.isConcurrentHandlingStarted()) {
				// Instead of postHandle and afterCompletion
				if (mappedHandler != null) {
					mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
				}
			}
			else {
				// Clean up any resources used by a multipart request.
				if (multipartRequestParsed) {
					cleanupMultipart(processedRequest);
				}
			}
		}
	}

	
Do we need view name translation?
/**
	 * Do we need view name translation?
	 */
	private void applyDefaultViewName(HttpServletRequest request, @Nullable ModelAndView mv) throws Exception {
		if (mv != null && !mv.hasView()) {
			String defaultViewName = getDefaultViewName(request);
			if (defaultViewName != null) {
				mv.setViewName(defaultViewName);
			}
		}
	}

	
Handle the result of handler selection and handler invocation, which is
either a ModelAndView or an Exception to be resolved to a ModelAndView.
/**
	 * Handle the result of handler selection and handler invocation, which is
	 * either a ModelAndView or an Exception to be resolved to a ModelAndView.
	 */
	private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
			@Nullable Exception exception) throws Exception {

		boolean errorView = false;

		if (exception != null) {
			if (exception instanceof ModelAndViewDefiningException) {
				logger.debug("ModelAndViewDefiningException encountered", exception);
				mv = ((ModelAndViewDefiningException) exception).getModelAndView();
			}
			else {
				Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
				mv = processHandlerException(request, response, handler, exception);
				errorView = (mv != null);
			}
		}

		// Did the handler return a view to render?
		if (mv != null && !mv.wasCleared()) {
			render(mv, request, response);
			if (errorView) {
				WebUtils.clearErrorRequestAttributes(request);
			}
		}
		else {
			if (logger.isTraceEnabled()) {
				logger.trace("No view rendering, null ModelAndView returned.");
			}
		}

		if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
			// Concurrent handling started during a forward
			return;
		}

		if (mappedHandler != null) {
			mappedHandler.triggerAfterCompletion(request, response, null);
		}
	}

	
Build a LocaleContext for the given request, exposing the request's primary locale as current locale.
The default implementation uses the dispatcher's LocaleResolver to obtain the current locale,
which might change during a request.
Params:
request – current HTTP request
Returns:
the corresponding LocaleContext/**
	 * Build a LocaleContext for the given request, exposing the request's primary locale as current locale.
	 * <p>The default implementation uses the dispatcher's LocaleResolver to obtain the current locale,
	 * which might change during a request.
	 * @param request current HTTP request
	 * @return the corresponding LocaleContext
	 */
	@Override
	protected LocaleContext buildLocaleContext(final HttpServletRequest request) {
		LocaleResolver lr = this.localeResolver;
		if (lr instanceof LocaleContextResolver) {
			return ((LocaleContextResolver) lr).resolveLocaleContext(request);
		}
		else {
			return () -> (lr != null ? lr.resolveLocale(request) : request.getLocale());
		}
	}

	
Convert the request into a multipart request, and make multipart resolver available.
If no multipart resolver is set, simply use the existing request.
Params:
request – current HTTP request
See Also:
MultipartResolver.resolveMultipart
Returns:
the processed request (multipart wrapper if necessary)/**
	 * Convert the request into a multipart request, and make multipart resolver available.
	 * <p>If no multipart resolver is set, simply use the existing request.
	 * @param request current HTTP request
	 * @return the processed request (multipart wrapper if necessary)
	 * @see MultipartResolver#resolveMultipart
	 */
	protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
		if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) {
			if (WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class) != null) {
				if (request.getDispatcherType().equals(DispatcherType.REQUEST)) {
					logger.trace("Request already resolved to MultipartHttpServletRequest, e.g. by MultipartFilter");
				}
			}
			else if (hasMultipartException(request) ) {
				logger.debug("Multipart resolution previously failed for current request - " +
						"skipping re-resolution for undisturbed error rendering");
			}
			else {
				try {
					return this.multipartResolver.resolveMultipart(request);
				}
				catch (MultipartException ex) {
					if (request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) != null) {
						logger.debug("Multipart resolution failed for error dispatch", ex);
						// Keep processing error dispatch with regular request handle below
					}
					else {
						throw ex;
					}
				}
			}
		}
		// If not returned before: return original request.
		return request;
	}

	
Check "javax.servlet.error.exception" attribute for a multipart exception.
/**
	 * Check "javax.servlet.error.exception" attribute for a multipart exception.
	 */
	private boolean hasMultipartException(HttpServletRequest request) {
		Throwable error = (Throwable) request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE);
		while (error != null) {
			if (error instanceof MultipartException) {
				return true;
			}
			error = error.getCause();
		}
		return false;
	}

	
Clean up any resources used by the given multipart request (if any).
Params:
request – current HTTP request
See Also:
MultipartResolver.cleanupMultipart/**
	 * Clean up any resources used by the given multipart request (if any).
	 * @param request current HTTP request
	 * @see MultipartResolver#cleanupMultipart
	 */
	protected void cleanupMultipart(HttpServletRequest request) {
		if (this.multipartResolver != null) {
			MultipartHttpServletRequest multipartRequest =
					WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class);
			if (multipartRequest != null) {
				this.multipartResolver.cleanupMultipart(multipartRequest);
			}
		}
	}

	
Return the HandlerExecutionChain for this request.
Tries all handler mappings in order.
Params:
request – current HTTP request
Returns:
the HandlerExecutionChain, or null if no handler could be found/**
	 * Return the HandlerExecutionChain for this request.
	 * <p>Tries all handler mappings in order.
	 * @param request current HTTP request
	 * @return the HandlerExecutionChain, or {@code null} if no handler could be found
	 */
	@Nullable
	protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
		if (this.handlerMappings != null) {
			for (HandlerMapping mapping : this.handlerMappings) {
				HandlerExecutionChain handler = mapping.getHandler(request);
				if (handler != null) {
					return handler;
				}
			}
		}
		return null;
	}

	
No handler found -> set appropriate HTTP response status.
Params:
request – current HTTP request
response – current HTTP response
Throws:
Exception – if preparing the response failed/**
	 * No handler found -> set appropriate HTTP response status.
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @throws Exception if preparing the response failed
	 */
	protected void noHandlerFound(HttpServletRequest request, HttpServletResponse response) throws Exception {
		if (pageNotFoundLogger.isWarnEnabled()) {
			pageNotFoundLogger.warn("No mapping for " + request.getMethod() + " " + getRequestUri(request));
		}
		if (this.throwExceptionIfNoHandlerFound) {
			throw new NoHandlerFoundException(request.getMethod(), getRequestUri(request),
					new ServletServerHttpRequest(request).getHeaders());
		}
		else {
			response.sendError(HttpServletResponse.SC_NOT_FOUND);
		}
	}

	
Return the HandlerAdapter for this handler object.
Params:
handler – the handler object to find an adapter for
Throws:
ServletException – if no HandlerAdapter can be found for the handler. This is a fatal error./**
	 * Return the HandlerAdapter for this handler object.
	 * @param handler the handler object to find an adapter for
	 * @throws ServletException if no HandlerAdapter can be found for the handler. This is a fatal error.
	 */
	protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
		if (this.handlerAdapters != null) {
			for (HandlerAdapter adapter : this.handlerAdapters) {
				if (adapter.supports(handler)) {
					return adapter;
				}
			}
		}
		throw new ServletException("No adapter for handler [" + handler +
				"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
	}

	
Determine an error ModelAndView via the registered HandlerExceptionResolvers.
Params:
request – current HTTP request
response – current HTTP response
handler – the executed handler, or null if none chosen at the time of the exception (for example, if multipart resolution failed)
ex – the exception that got thrown during handler execution
Throws:
Exception – if no error ModelAndView found
Returns:
a corresponding ModelAndView to forward to/**
	 * Determine an error ModelAndView via the registered HandlerExceptionResolvers.
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @param handler the executed handler, or {@code null} if none chosen at the time of the exception
	 * (for example, if multipart resolution failed)
	 * @param ex the exception that got thrown during handler execution
	 * @return a corresponding ModelAndView to forward to
	 * @throws Exception if no error ModelAndView found
	 */
	@Nullable
	protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
			@Nullable Object handler, Exception ex) throws Exception {

		// Success and error responses may use different content types
		request.removeAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);

		// Check registered HandlerExceptionResolvers...
		ModelAndView exMv = null;
		if (this.handlerExceptionResolvers != null) {
			for (HandlerExceptionResolver resolver : this.handlerExceptionResolvers) {
				exMv = resolver.resolveException(request, response, handler, ex);
				if (exMv != null) {
					break;
				}
			}
		}
		if (exMv != null) {
			if (exMv.isEmpty()) {
				request.setAttribute(EXCEPTION_ATTRIBUTE, ex);
				return null;
			}
			// We might still need view name translation for a plain error model...
			if (!exMv.hasView()) {
				String defaultViewName = getDefaultViewName(request);
				if (defaultViewName != null) {
					exMv.setViewName(defaultViewName);
				}
			}
			if (logger.isTraceEnabled()) {
				logger.trace("Using resolved error view: " + exMv, ex);
			}
			if (logger.isDebugEnabled()) {
				logger.debug("Using resolved error view: " + exMv);
			}
			WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());
			return exMv;
		}

		throw ex;
	}

	
Render the given ModelAndView.
This is the last stage in handling a request. It may involve resolving the view by name.
Params:
mv – the ModelAndView to render
request – current HTTP servlet request
response – current HTTP servlet response
Throws:
ServletException – if view is missing or cannot be resolved
Exception – if there's a problem rendering the view/**
	 * Render the given ModelAndView.
	 * <p>This is the last stage in handling a request. It may involve resolving the view by name.
	 * @param mv the ModelAndView to render
	 * @param request current HTTP servlet request
	 * @param response current HTTP servlet response
	 * @throws ServletException if view is missing or cannot be resolved
	 * @throws Exception if there's a problem rendering the view
	 */
	protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
		// Determine locale for request and apply it to the response.
		Locale locale =
				(this.localeResolver != null ? this.localeResolver.resolveLocale(request) : request.getLocale());
		response.setLocale(locale);

		View view;
		String viewName = mv.getViewName();
		if (viewName != null) {
			// We need to resolve the view name.
			view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
			if (view == null) {
				throw new ServletException("Could not resolve view with name '" + mv.getViewName() +
						"' in servlet with name '" + getServletName() + "'");
			}
		}
		else {
			// No need to lookup: the ModelAndView object contains the actual View object.
			view = mv.getView();
			if (view == null) {
				throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +
						"View object in servlet with name '" + getServletName() + "'");
			}
		}

		// Delegate to the View object for rendering.
		if (logger.isTraceEnabled()) {
			logger.trace("Rendering view [" + view + "] ");
		}
		try {
			if (mv.getStatus() != null) {
				response.setStatus(mv.getStatus().value());
			}
			view.render(mv.getModelInternal(), request, response);
		}
		catch (Exception ex) {
			if (logger.isDebugEnabled()) {
				logger.debug("Error rendering view [" + view + "]", ex);
			}
			throw ex;
		}
	}

	
Translate the supplied request into a default view name.
Params:
request – current HTTP servlet request
Throws:
Exception – if view name translation failed
Returns:
the view name (or null if no default found)/**
	 * Translate the supplied request into a default view name.
	 * @param request current HTTP servlet request
	 * @return the view name (or {@code null} if no default found)
	 * @throws Exception if view name translation failed
	 */
	@Nullable
	protected String getDefaultViewName(HttpServletRequest request) throws Exception {
		return (this.viewNameTranslator != null ? this.viewNameTranslator.getViewName(request) : null);
	}

	
Resolve the given view name into a View object (to be rendered).
The default implementations asks all ViewResolvers of this dispatcher.
Can be overridden for custom resolution strategies, potentially based on
specific model attributes or request parameters.
Params:
viewName – the name of the view to resolve
model – the model to be passed to the view
locale – the current locale
request – current HTTP servlet request
Throws:
Exception – if the view cannot be resolved
(typically in case of problems creating an actual View object)
See Also:
ViewResolver.resolveViewName
Returns:
the View object, or null if none found/**
	 * Resolve the given view name into a View object (to be rendered).
	 * <p>The default implementations asks all ViewResolvers of this dispatcher.
	 * Can be overridden for custom resolution strategies, potentially based on
	 * specific model attributes or request parameters.
	 * @param viewName the name of the view to resolve
	 * @param model the model to be passed to the view
	 * @param locale the current locale
	 * @param request current HTTP servlet request
	 * @return the View object, or {@code null} if none found
	 * @throws Exception if the view cannot be resolved
	 * (typically in case of problems creating an actual View object)
	 * @see ViewResolver#resolveViewName
	 */
	@Nullable
	protected View resolveViewName(String viewName, @Nullable Map<String, Object> model,
			Locale locale, HttpServletRequest request) throws Exception {

		if (this.viewResolvers != null) {
			for (ViewResolver viewResolver : this.viewResolvers) {
				View view = viewResolver.resolveViewName(viewName, locale);
				if (view != null) {
					return view;
				}
			}
		}
		return null;
	}

	private void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response,
			@Nullable HandlerExecutionChain mappedHandler, Exception ex) throws Exception {

		if (mappedHandler != null) {
			mappedHandler.triggerAfterCompletion(request, response, ex);
		}
		throw ex;
	}

	
Restore the request attributes after an include.
Params:
request – current HTTP request
attributesSnapshot – the snapshot of the request attributes before the include/**
	 * Restore the request attributes after an include.
	 * @param request current HTTP request
	 * @param attributesSnapshot the snapshot of the request attributes before the include
	 */
	@SuppressWarnings("unchecked")
	private void restoreAttributesAfterInclude(HttpServletRequest request, Map<?,?> attributesSnapshot) {
		// Need to copy into separate Collection here, to avoid side effects
		// on the Enumeration when removing attributes.
		Set<String> attrsToCheck = new HashSet<>();
		Enumeration<?> attrNames = request.getAttributeNames();
		while (attrNames.hasMoreElements()) {
			String attrName = (String) attrNames.nextElement();
			if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
				attrsToCheck.add(attrName);
			}
		}

		// Add attributes that may have been removed
		attrsToCheck.addAll((Set<String>) attributesSnapshot.keySet());

		// Iterate over the attributes to check, restoring the original value
		// or removing the attribute, respectively, if appropriate.
		for (String attrName : attrsToCheck) {
			Object attrValue = attributesSnapshot.get(attrName);
			if (attrValue == null){
				request.removeAttribute(attrName);
			}
			else if (attrValue != request.getAttribute(attrName)) {
				request.setAttribute(attrName, attrValue);
			}
		}
	}

	private static String getRequestUri(HttpServletRequest request) {
		String uri = (String) request.getAttribute(WebUtils.INCLUDE_REQUEST_URI_ATTRIBUTE);
		if (uri == null) {
			uri = request.getRequestURI();
		}
		return uri;
	}

}