/*
 * Copyright 2002-2019 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
 *
 *      https://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.
 *
 * <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. */
        public static final String MULTIPART_RESOLVER_BEAN_NAME = "multipartResolver";

        /** 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. */
        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 #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 #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 #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.
         */
        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 #setDetectAllViewResolvers
         */
        public static final String VIEW_RESOLVER_BEAN_NAME = "viewResolver";

        /**
         * 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 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 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 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 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 {@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" {@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 {@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 a
         * {@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. */
        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.
         */
        private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";

        /**
         * 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. */
        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?. */
        private boolean detectAllHandlerMappings = true;

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

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

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

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

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

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

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

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

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

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

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

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

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

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


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

        /**
         * 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.
         * <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.
         * <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.
         * <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.
         * <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.
         * <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.
         * <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.
         * <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.
         * <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 {@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 {@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.
         * @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 {@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.
         * <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.
         * <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.
         * <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 {@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 queryString = request.getQueryString();
                        String queryClause = (StringUtils.hasLength(queryString) ? "?" + queryString : "");
                        String dispatchType = (!request.getDispatcherType().equals(DispatcherType.REQUEST) ?
                                        "\"" + request.getDispatcherType().name() + "\" dispatch for " : "");
                        String message = (dispatchType + request.getMethod() + " \"" + getRequestUri(request) +
                                        queryClause + "\", 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.
         * <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?
         */
        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.
         */
        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) {
                        // Exception (if any) is already handled..
                        mappedHandler.triggerAfterCompletion(request, response, null);
                }
        }

        /**
         * 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.
         * <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.
         */
        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).
         * @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.
         * <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.
         * @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.
         * @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.
         * @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);
                        }
                        else if (logger.isDebugEnabled()) {
                                logger.debug("Using resolved error view: " + exMv);
                        }
                        WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());
                        return exMv;
                }

                throw ex;
        }

        /**
         * 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.
         * @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).
         * <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.
         * @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;
        }

}