Servlet和springMVC

来源:https://www.cnblogs.com/july7/archive/2023/03/25/17255981.html
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什麼是Servlet? Servlet是使用Java語言編寫的運行在伺服器端的程式。狹義的Servlet是指Java語言實現的一個介面，廣義的Servlet是指任何實現了這個Servlet介面的類，一般情況下，人們將Servlet理解為後者。Servlet 主要用於處理客戶端傳來的 HTTP 請求， ...


什麼是Servlet?

  1. Servlet是使用Java語言編寫的運行在伺服器端的程式。狹義的Servlet是指Java語言實現的一個介面，廣義的Servlet是指任何實現了這個Servlet介面的類，一般情況下，人們將Servlet理解為後者。Servlet 主要用於處理客戶端傳來的 HTTP 請求，並返回一個響應，它能夠處理的請求有doGet()和doPost()等方法
  2. Servlet由Servlet容器提供，所謂的Servlet容器是指提供了Servlet 功能的伺服器（本書中指Tomcat）,Servlet容器將Servlet動態地載入到伺服器上。與HTTP 協議相關的Servlet使用HTTP請求和HTTP響應與客戶端進行交互。因此，Servlet容器支持所有HTTP協議的請求和響應。Servlet應用程式的體繫結構如圖所示。<<javaWeb程式設計教程>>

什麼是SpringMVC?

  1. Spring MVC一開始就定位於一個較為鬆散的組合，展示給用戶的視圖（View）、控制器返回的數據模型（Model）、定位視圖的視圖解析器（ViewResolver）和處理適配器（HandlerAdapter）等內容都是獨立的。換句話說，通過Spring MVC很容易把後臺的數據轉換為各種類型的數據，以滿足移動互聯網數據多樣化的要求。例如，Spring MVC可以十分方便地轉換為目前最常用的JSON數據集，也可以轉換為PDF、Excel和XML等。加之Spring MVC是基於Spring基礎框架派生出來的Web框架，所以它天然就可以十分方便地整合到Spring框架中，而Spring整合Struts2還是比較繁複的.
  2. mvc架構設計:處理請求先到達控制器（Controller），控制器的作用是進行請求分發，這樣它會根據請求的內容去訪問模型層（Model）；在現今互聯網系統中，數據主要從資料庫和NoSQL中來，而且對於資料庫而言往往還存在事務的機制，為了適應這樣的變化，設計者會把模型層再細分為兩層，即服務層（Service）和數據訪問層（DAO）；當控制器獲取到由模型層返回的數據後，就將數據渲染到視圖中，這樣就能夠展現給用戶了

  3.  

     圖取自於<<深入淺出springboot2.x>>書籍

 

思考和疑問

早些年的時候,使用servlet開發web程式, 一般都是繼承HttpServlet介面,請求訪問時直接根據類名調用.但這樣寫的結果是,一個類只能處理一個請求.項目結構大概長這樣

使用SpringMVC框架後,只需要配置簡單的@RequestMapping("")就可以找到對應的方法,原來的servlet呢? 對springMVC的瞭解還是不夠詳細,所以

繼續探討以下幾個問題

1.SpringMVC如何代替Servlet?

 

 

 可以看到DispatcherServlet繼承自HttpServlet,  前端控制器其實就相當於一個Servlet.

 2. SpringMVC的工作流程?

 

圖取自於<<深入淺出springboot2.x>>書籍

基於springboot開發使得SpringMVC的使用更為簡便,可以通過Spring Boot的配置來定製這些組件的初始化

  1. /*
 * 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.
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