Spring MVC -- Spring MVC入门

本篇博客首先介绍Spring MVC的优点，然后介绍Spring MVC的基本组件，包括DispatcherServlet，并学习如何开发一个“传统风格”的控制器，这是在Spring 2.5版本之前开发控制器的唯一方式。之所以介绍传统方式，是因为我们可能不得不在基于旧版Spring的遗留代码上工作。对于新的应用，我们可以采用基于注解的控制器。

此外，还会介绍Sping MVC配置，大部分的Spring MVC应用会采用一个XML文档来定义应用中所用到的bean（Spring管理的对象称为bean）。更多Spring MVC配置文件的信息可以参考博客Spring MVC -- Spring框架入门（IoC、DI以及XML配置文件）。

一 Spring MVC的优点

若采用Spring MVC框架开发一个应用程序，我们通常要负责编写一个DispatcherServlet（实际上就是一个Servlet控制器，实现了抽象类HttpServlet）和控制类（注意这里的控制类不是指的Servlet控制器，而是指实现了Controller接口的类，后面会详细介绍）。其中，DispatcherServlet必须能够做一下事情：

1. 根据URL调用相应的action；
2. 实例化正确的控制器类；
3. 根据页面请求参数值来构造表单bean；
4. 调用控制器对象的相应方法；
5. 转到一个试图（jsp页面）。

幸运的是，Spring MVC是一个包含了DispatcherServlet的MVC框架。它调用控制器方法并转发到视图。使用Spring MVC的第一个好处是，不需要编写DispatcherServlet。以下是Spring MVC具有的能加速开发的功能的列表：

• Spring MVC提供了一个DispatcherServlet，无需额外开发；
• Spring MVC使用了基于XML的配置文件，可以编辑，而无需重新编译应用程序；
• Spring MVC实例化控制器，并根据用户输入来构造bean；
• Spring MVC可以自动绑定用户输入，并正确地转换数据类型。例如，Spring MVC能自动解析字符串，并设置float或decimal类型的属性；
• Spring MVC可以校验用户输入，若校验不通过，则重定向回输入表单。输入校验是可选的，支持编程方式及声明方式。关于这一点，Spring MVC内置了常见的校验器；
• Spring MVC是Spring框架的一部分，可以利用Spring提供的其它能力；
• Spring MVC支持国际化和本地化，支持根据用户区域显示多国语言；
• Spring MVC支持多种视图技术。最常见的jsp技术以及其他技术包括Velocity和FreeMarker。

二 Spring MVC基本组件

1、Spring MVC的DispatcherServlet

在Spring MVC -- MVC设计模式(演示4个基于MVC框架的案例)中我们创建了一个简单的基于MVC框架的Web应用，应用中包括一个充当调度员的控制器(servlet或者是filter)。基于Spring MVC，则无需如此。Spring MVC中自带了一个开箱即用的DispatcherServlet，该servlei全名是org.springframework.web.servlet.DispacterServlet。源码如下，有兴趣可以看一下：

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

    /** Log category to use when no mapped handler is found for a request. */
    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 query = StringUtils.isEmpty(request.getQueryString()) ? "" : "?" + request.getQueryString();
            String dispatchType = (!request.getDispatcherType().equals(DispatcherType.REQUEST) ?
                    """ + request.getDispatcherType().name() + "" dispatch for " : "");
            String message = (dispatchType + request.getMethod() + " "" + getRequestUri(request) +
                    query + "", parameters={" + params + "}");

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

    /**
     * Process the actual dispatching to the handler.
     * <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) {
            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);
            }
            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;
    }

}

要使用这个servlet，需要在部署描述符文件(web.xml)中使用servlet和servlet-mapping元素来配置它，如下所示：

    <servlet>
        <servlet-name>springmvc</servlet-name>
        <servlet-class>
            org.springframework.web.servlet.DispatcherServlet
        </servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>springmvc</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
    

servlet元素内的load-on-startup元素是可选的，如果它存在，则它将在应用程序启动时装载该servlet并调用它的init()方法。若它不存在，则在该servlet第一个请求时加载它。

DispatcherServlet将使用Spring MVC诸多默认的组件。此外，初始化时，它会寻找在应用程序的WEB-INF目录下的一个配置文件，该配置文件的命名规则如下：

servletName-servlet.xml

其中，servletName是部署描述符中的DispatcherServlet的名称（上面配置的 <servlet-name>springmvc</servlet-name>）。如果这个servlet的名称是springmvc，则应在应用程序目录的WEB-INF下对应的文件时springmvc-servlet.xml。

此外，也可以把Spring MVC的配置文件放在应用程序目录中的任何地方，只要告诉DispatcherServlet在哪里可以找到该文件。我们使用servlet声明下的一个init-param元素来做到这一点。init-param元素拥有一个值为contextConfigLocation的param-name元素，其param-value元素则包含配置文件的路径。例如，可以利用init-param元素将默认的文件名和文件路径更改为/WEB-INF/config/simple-config.xml。

    <servlet>
        <servlet-name>springmvc</servlet-name>
        <servlet-class>
            org.springframework.web.servlet.DispatcherServlet
        </servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/config/simple-config.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>springmvc</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

2、Controller接口

在Spring 2.5之前，开发一个控制器的唯一方法是实现org.springframework.web.servlet.mvc.Controller接口。源码如下：

/*
 * Copyright 2002-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      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.mvc;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.lang.Nullable;
import org.springframework.web.servlet.ModelAndView;

/**
 * Base Controller interface, representing a component that receives
 * {@code HttpServletRequest} and {@code HttpServletResponse}
 * instances just like a {@code HttpServlet} but is able to
 * participate in an MVC workflow. Controllers are comparable to the
 * notion of a Struts {@code Action}.
 *
 * <p>Any implementation of the Controller interface should be a
 * <i>reusable, thread-safe</i> class, capable of handling multiple
 * HTTP requests throughout the lifecycle of an application. To be able to
 * configure a Controller easily, Controller implementations are encouraged
 * to be (and usually are) JavaBeans.
 *
 * <h3><a name="workflow">Workflow</a></h3>
 *
 * <p>After a {@code DispatcherServlet} has received a request and has
 * done its work to resolve locales, themes, and suchlike, it then tries
 * to resolve a Controller, using a
 * {@link org.springframework.web.servlet.HandlerMapping HandlerMapping}.
 * When a Controller has been found to handle the request, the
 * {@link #handleRequest(HttpServletRequest, HttpServletResponse) handleRequest}
 * method of the located Controller will be invoked; the located Controller
 * is then responsible for handling the actual request and &mdash; if applicable
 * &mdash; returning an appropriate
 * {@link org.springframework.web.servlet.ModelAndView ModelAndView}.
 * So actually, this method is the main entry point for the
 * {@link org.springframework.web.servlet.DispatcherServlet DispatcherServlet}
 * which delegates requests to controllers.
 *
 * <p>So basically any <i>direct</i> implementation of the {@code Controller} interface
 * just handles HttpServletRequests and should return a ModelAndView, to be further
 * interpreted by the DispatcherServlet. Any additional functionality such as
 * optional validation, form handling, etc. should be obtained through extending
 * {@link org.springframework.web.servlet.mvc.AbstractController AbstractController}
 * or one of its subclasses.
 *
 * <h3>Notes on design and testing</h3>
 *
 * <p>The Controller interface is explicitly designed to operate on HttpServletRequest
 * and HttpServletResponse objects, just like an HttpServlet. It does not aim to
 * decouple itself from the Servlet API, in contrast to, for example, WebWork, JSF or Tapestry.
 * Instead, the full power of the Servlet API is available, allowing Controllers to be
 * general-purpose: a Controller is able to not only handle web user interface
 * requests but also to process remoting protocols or to generate reports on demand.
 *
 * <p>Controllers can easily be tested by passing in mock objects for the
 * HttpServletRequest and HttpServletResponse objects as parameters to the
 * {@link #handleRequest(HttpServletRequest, HttpServletResponse) handleRequest}
 * method. As a convenience, Spring ships with a set of Servlet API mocks
 * that are suitable for testing any kind of web components, but are particularly
 * suitable for testing Spring web controllers. In contrast to a Struts Action,
 * there is no need to mock the ActionServlet or any other infrastructure;
 * mocking HttpServletRequest and HttpServletResponse is sufficient.
 *
 * <p>If Controllers need to be aware of specific environment references, they can
 * choose to implement specific awareness interfaces, just like any other bean in a
 * Spring (web) application context can do, for example:
 * <ul>
 * <li>{@code org.springframework.context.ApplicationContextAware}</li>
 * <li>{@code org.springframework.context.ResourceLoaderAware}</li>
 * <li>{@code org.springframework.web.context.ServletContextAware}</li>
 * </ul>
 *
 * <p>Such environment references can easily be passed in testing environments,
 * through the corresponding setters defined in the respective awareness interfaces.
 * In general, it is recommended to keep the dependencies as minimal as possible:
 * for example, if all you need is resource loading, implement ResourceLoaderAware only.
 * Alternatively, derive from the WebApplicationObjectSupport base class, which gives
 * you all those references through convenient accessors but requires an
 * ApplicationContext reference on initialization.
 *
 * <p>Controllers can optionally implement the {@link LastModified} interface.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see LastModified
 * @see SimpleControllerHandlerAdapter
 * @see AbstractController
 * @see org.springframework.mock.web.MockHttpServletRequest
 * @see org.springframework.mock.web.MockHttpServletResponse
 * @see org.springframework.context.ApplicationContextAware
 * @see org.springframework.context.ResourceLoaderAware
 * @see org.springframework.web.context.ServletContextAware
 * @see org.springframework.web.context.support.WebApplicationObjectSupport
 */
@FunctionalInterface
public interface Controller {

    /**
     * Process the request and return a ModelAndView object which the DispatcherServlet
     * will render. A {@code null} return value is not an error: it indicates that
     * this object completed request processing itself and that there is therefore no
     * ModelAndView to render.
     * @param request current HTTP request
     * @param response current HTTP response
     * @return a ModelAndView to render, or {@code null} if handled directly
     * @throws Exception in case of errors
     */
    @Nullable
    ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception;

}

这个接口公开了一个handleRequest()方法，下面是该方法的签名：

ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception;

其实现类可以访问对应请求的HttpServletRequest 和HttpServletResponse 还必须返回一个ModelAndView 对象，它包含视图路径或视图路径和模型。

Controller接口的实现类只能处理一个单一动作(action)，而一个基于注解的控制器可以同时支持多个请求处理动作，并且无需实现任何接口（下一篇博客会介绍）。

三 第一个Spring MVC应用

本节的示例应用程序springmvc-intro1展示了基本的Spring MVC应用。该应用程序和Spring MVC -- MVC设计模式(演示4个基于MVC框架的案例)中的appdesign1应用非常相似，专用于展示Spring MVC是如何工作的。springmvc-intro1包含两个控制器类，类似于appdesign1中的控制器类。

1、目录结构

目录结构如下：

注意：WEB-INF/lib目录包含了Spring MVC所需要的所有jar文件。特别需要注意的是spring-webmvc-5.1.6.RELEASE.jar包含了DispacterServlet类。还要注意Spring MVC依赖于Apache Commons Logging组件，没有它，Spring MVC应用程序就无法正常工作。这些jar包的下载可以参考博客Spring MVC -- Spring框架入门（IoC、DI以及XML配置文件）。

该示例应用的所有jsp页面都存放在/WEB-INF/jsp目录下，这样就可以避免直接通过浏览器访问，但是控制器仍然可以转发请求到这些页面。

2、部署描述符(web.xml文件)和Spring MVC配置文件

部署描述符(web.xml文件)：

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.1" 
        xmlns="http://xmlns.jcp.org/xml/ns/javaee" 
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
        xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee 
            http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"> 
    <servlet>
        <servlet-name>springmvc</servlet-name>
        <servlet-class>
            org.springframework.web.servlet.DispatcherServlet
        </servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>springmvc</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
    
</web-app>

这里告诉了Servlet/JSP容器，我们将使用Spring MVC的DispatcherServlet，并通过url-pattern元素值配置为“/”，将所有的URL映射到该servlet。由于servlet元素下没有init-param元素，所以Spring MVC的配置文件在/WEB-INF文件夹下，并按照通常的命名约定：

Spring MVC配置文件(springmvc-servlet.xml)：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd">
       
    <bean name="/input-product" class="controller.InputProductController"/>
    <bean name="/save-product" class="controller.SaveProductController"/>

</beans>

这里声明了InputProductController和SaveProductController两个控制器，并分别映射到/input-product和/save-product。

3、Controller类

springmvc-intro1应用程序有InputProductController和SaveProductController这两个控制器，分别实现了Controller接口。

InputProductController类：

package controller;

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.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.Controller;

public class InputProductController implements Controller {

    private static final Log logger = LogFactory
            .getLog(InputProductController.class);

    @Override
    public ModelAndView handleRequest(HttpServletRequest request,
            HttpServletResponse response) throws Exception {
        logger.info("InputProductController called");
        return new ModelAndView("/WEB-INF/jsp/ProductForm.jsp");
    }

}

InputProductController类的handleRequest()方法只是返回一个ModelAndView ，包含一个视图，但没有模型。因此，该请求将被转发到/WEB-INF/jsp/ProductForm.jsp页面。

SaveProductController类：

package controller;

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.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.Controller;

import domain.Product;
import form.ProductForm;

public class SaveProductController implements Controller {

    private static final Log logger = LogFactory
            .getLog(SaveProductController.class);

    @Override
    public ModelAndView handleRequest(HttpServletRequest request,
            HttpServletResponse response) throws Exception {
        logger.info("SaveProductController called");
        //创建表单类 保存表单提交的信息
        ProductForm productForm = new ProductForm();
        // populate action properties
        productForm.setName(request.getParameter("name"));
        productForm.setDescription(request.getParameter("description"));
        productForm.setPrice(request.getParameter("price"));

        // create model  创建Product模型对象
        Product product = new Product();
        product.setName(productForm.getName());
        product.setDescription(productForm.getDescription());
        try {
            product.setPrice(Float.parseFloat(productForm.getPrice()));
        } catch (NumberFormatException e) {
        }

        // insert code to save Product

        return new ModelAndView("/WEB-INF/jsp/ProductDetails.jsp", "product",
                product);
    }

}

SaveProductController类的handleRequest()方法中，首先用请求参数创建一个ProductForm对象，然后它根据ProductForm对象创建Product对象。由于ProductForm的price属性是一个字符串，而其在Product类对应的是一个float，此处类型转换是必要的。

SaveProductController类的handleRequest()方法最后返回的ModelAndView模型包含了视图的路径、模型名称以及模型（Product对象）。该模型将提供给目标视图，用于界面显示。

其中ProductForm类如下：

package form;

public class ProductForm {
    private String name;
    private String description;
    private String price;

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }
    public String getPrice() {
        return price;
    }
    public void setPrice(String price) {
        this.price = price;
    }
}

Product类如下：

package domain;
import java.io.Serializable;

public class Product implements Serializable {
    private static final long serialVersionUID = 748392348L;
    private String name;
    private String description;
    private float price;

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }
    public float getPrice() {
        return price;
    }
    public void setPrice(float price) {
        this.price = price;
    }
}

4、视图

springmvc-intro1应用程序包含两个jsp页面：ProductForm.jsp页面和ProductDetails页面：

ProductForm.jsp：

<!DOCTYPE html>
<html>
<head>
<title>Add Product Form</title>
<style type="text/css">@import url(css/main.css);</style>
</head>
<body>

<div id="global">
<form action="save-product" method="post">
    <fieldset>
        <legend>Add a product</legend>
            <p>
                <label for="name">Product Name: </label>
                <input type="text" id="name" name="name" 
                    tabindex="1">
            </p>
            <p>
                <label for="description">Description: </label>
                <input type="text" id="description" 
                    name="description" tabindex="2">
            </p>
            <p>
                <label for="price">Price: </label>
                <input type="text" id="price" name="price" 
                    tabindex="3">
            </p>
            <p id="buttons">
                <input id="reset" type="reset" tabindex="4">
                <input id="submit" type="submit" tabindex="5" 
                    value="Add Product">
            </p>
    </fieldset>
</form>
</div>
</body>
</html>

ProductDetails.jsp：

<!DOCTYPE html>
<html>
<head>
<title>Save Product</title>
<style type="text/css">@import url(css/main.css);</style>
</head>
<body>
<div id="global">
    <h4>The product has been saved.</h4>
    <p>
        <h5>Details:</h5>
        Product Name: ${product.name}<br/>
        Description: ${product.description}<br/>
        Price: $${product.price}
    </p>
</div>
</body>
</html>

ProductDetails页面通过EL表达式语言访问product对象的各种属性。

main.css：

#global {
    text-align: left;
    border: 1px solid #dedede;
    background: #efefef;
    width: 560px;
    padding: 20px;
    margin: 100px auto;
}

form {
  font:100% verdana;
  min-width: 500px;
  max-width: 600px;
  width: 560px;
}

form fieldset {
  border-color: #bdbebf;
  border-width: 3px;
  margin: 0;
}

legend {
    font-size: 1.3em;
}

form label { 
    width: 250px;
    display: block;
    float: left;
    text-align: right;
    padding: 2px;
}

#buttons {
    text-align: right;
}
#errors, li {
    color: red;
}

5、测试应用

将项目部署到tomcat服务器，然后启动服务器，假设示例应用运行在本机的8000端口上，则可以通过如下URL访问应用：

http://localhost:8008/springmvc-intro1/input-product

会看到如下产品表单页面：

 

在表单中输入相应的值后单击Add Product按钮，会在下一页中看到产品属性：

注意：price应该输入一个合法数字，不然就会设置为float型默认值0.0。

四 视图解析器

Spring MVC中的视图解析器复制解析视图。可以通过在XML配置文件中定义一个ViewResolver来配置视图解析器，如下：

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean name="/input-product" class="controller.InputProductController"/>
    <bean name="/save-product" class="controller.SaveProductController"/>
    <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <property name="suffix" value=".jsp"/>
    </bean>
</beans>

视图解析器配置有前缀和后缀两个属性。这样一来，view路径将缩短。例如：仅需提供“myPage”，而不必再将视图路径设置为/WEB-INF/jsp/myPage.jsp，视图解析器将会自动增加前缀和后缀。

以springmvc-intro2应用为例，该例子和springmvc-intro1应用类似，只是调整了配置文件的名称和路径。此外，它还配置了默认的视图解析器，为所有视图路径增加前缀和后缀：

我们可以看一下InputProductController的代码：

package controller;

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.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.Controller;

public class InputProductController implements Controller {
    
    private static final Log logger = LogFactory.getLog(InputProductController.class);
    
    @Override
    public ModelAndView handleRequest(HttpServletRequest request,
            HttpServletResponse response) throws Exception {
        logger.info("InputProductController called");
        return new ModelAndView("ProductForm");
    }

}

我们可以看到返回的视图名由springmvc-intro1中的/WEB-INF/jsp/ProductForm.jsp变成了ProductForm。

此外，在springmvc-intro2中，Spring MVC配置文件springmvc-config.xml被移动到/WEB-INF/config目录下。为了让Spring MVC可以正确加载到该配置文件，需要将文件路径配置到Spring MVC的DispatcherServlet。springmvc-intro2的web.xml配置文件如下：

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.1" 
        xmlns="http://xmlns.jcp.org/xml/ns/javaee" 
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
        xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee 
            http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"> 
    <servlet>
        <servlet-name>springmvc</servlet-name>
        <servlet-class>
            org.springframework.web.servlet.DispatcherServlet
        </servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/config/springmvc-config.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>    
    </servlet>

    <servlet-mapping>
        <servlet-name>springmvc</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
</web-app>

需要特别注意的是web.xml文件中的init-param元素。如果要使用非默认配置文件的命名和路径，需要使用名为contextConfigLocation的init-param，其值应为配置文件在应用中的相对路径。

五 总结

下面我们来总结一下使用Spring MVC框架的Web应用，用户通过浏览器请求服务器的响应流程，我们以URL：http://localhost:8008/springmvc-intro1/input-product为例：

• 请求首先被应用程序的web.xml文件拦截，通过url-pattern元素值配置为“/”，将所有的URL映射到Spring MVC的DispatcherServlet；

      <servlet>
          <servlet-name>springmvc</servlet-name>
          <servlet-class>
              org.springframework.web.servlet.DispatcherServlet
          </servlet-class>
          <load-on-startup>1</load-on-startup>
      </servlet>
  
      <servlet-mapping>
          <servlet-name>springmvc</servlet-name>
          <url-pattern>/</url-pattern>
      </servlet-mapping>

• DispatcherServlet在第一次加载时会调用init()方法进行初始化，会寻找Spring MVC配置文件；

• 通过配置文件中的bean元素，将URL映射到控制器类；

   <bean name="/input-product" class="controller.InputProductController"/>

• 执行控制器的handleRequest方法，并返回一个ModelAndView。

      public ModelAndView handleRequest(HttpServletRequest request,
              HttpServletResponse response) throws Exception {
          logger.info("InputProductController called");
          return new ModelAndView("/WEB-INF/jsp/ProductForm.jsp");
      }

本篇博客是Spring MVC的入门介绍，我们学习了一个简单的Spring MVC应用。在Srping MVC中，我们无需编写自己的DispatcherServlet，并通过实现控制器接口来编写控制器，这是传统风格的控制器。从Spring 2.5版本开始，Spring提供了一个更好的开发控制器的方式，如采用注解。下一篇博客将会详细介绍。

参考文章

[1]Spring MVC学习指南