DispatcherServlet源码注解分析

 1 /*
   2  * Copyright 2002-2017 the original author or authors.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  *      http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16 
  17 package org.springframework.web.servlet;
  18 
  19 import java.io.IOException;
  20 import java.util.ArrayList;
  21 import java.util.Collections;
  22 import java.util.Enumeration;
  23 import java.util.HashMap;
  24 import java.util.HashSet;
  25 import java.util.LinkedList;
  26 import java.util.List;
  27 import java.util.Locale;
  28 import java.util.Map;
  29 import java.util.Properties;
  30 import java.util.Set;
  31 import javax.servlet.ServletContext;
  32 import javax.servlet.ServletException;
  33 import javax.servlet.http.HttpServletRequest;
  34 import javax.servlet.http.HttpServletResponse;
  35 
  36 import org.apache.commons.logging.Log;
  37 import org.apache.commons.logging.LogFactory;
  38 
  39 import org.springframework.beans.factory.BeanFactoryUtils;
  40 import org.springframework.beans.factory.BeanInitializationException;
  41 import org.springframework.beans.factory.NoSuchBeanDefinitionException;
  42 import org.springframework.context.ApplicationContext;
  43 import org.springframework.context.ConfigurableApplicationContext;
  44 import org.springframework.context.i18n.LocaleContext;
  45 import org.springframework.core.annotation.AnnotationAwareOrderComparator;
  46 import org.springframework.core.io.ClassPathResource;
  47 import org.springframework.core.io.support.PropertiesLoaderUtils;
  48 import org.springframework.http.server.ServletServerHttpRequest;
  49 import org.springframework.ui.context.ThemeSource;
  50 import org.springframework.util.ClassUtils;
  51 import org.springframework.util.StringUtils;
  52 import org.springframework.web.context.WebApplicationContext;
  53 import org.springframework.web.context.request.ServletWebRequest;
  54 import org.springframework.web.context.request.async.WebAsyncManager;
  55 import org.springframework.web.context.request.async.WebAsyncUtils;
  56 import org.springframework.web.multipart.MultipartException;
  57 import org.springframework.web.multipart.MultipartHttpServletRequest;
  58 import org.springframework.web.multipart.MultipartResolver;
  59 import org.springframework.web.util.NestedServletException;
  60 import org.springframework.web.util.WebUtils;
  61 
  62 /**
  63  * Central dispatcher for HTTP request handlers/controllers, e.g. for web UI controllers
  64  * or HTTP-based remote service exporters. Dispatches to registered handlers for processing
  65  * a web request, providing convenient mapping and exception handling facilities.
  66  *
  67  * <p>This servlet is very flexible: It can be used with just about any workflow, with the
  68  * installation of the appropriate adapter classes. It offers the following functionality
  69  * that distinguishes it from other request-driven web MVC frameworks:
  70  *
  71  * <ul>
  72  * <li>It is based around a JavaBeans configuration mechanism.
  73  *
  74  * <li>It can use any {@link HandlerMapping} implementation - pre-built or provided as part
  75  * of an application - to control the routing of requests to handler objects. Default is
  76  * {@link org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping} and
  77  * {@link org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping}.
  78  * HandlerMapping objects can be defined as beans in the servlet's application context,
  79  * implementing the HandlerMapping interface, overriding the default HandlerMapping if
  80  * present. HandlerMappings can be given any bean name (they are tested by type).
  81  *
  82  * <li>It can use any {@link HandlerAdapter}; this allows for using any handler interface.
  83  * Default adapters are {@link org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter},
  84  * {@link org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter}, for Spring's
  85  * {@link org.springframework.web.HttpRequestHandler} and
  86  * {@link org.springframework.web.servlet.mvc.Controller} interfaces, respectively. A default
  87  * {@link org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter}
  88  * will be registered as well. HandlerAdapter objects can be added as beans in the
  89  * application context, overriding the default HandlerAdapters. Like HandlerMappings,
  90  * HandlerAdapters can be given any bean name (they are tested by type).
  91  *
  92  * <li>The dispatcher's exception resolution strategy can be specified via a
  93  * {@link HandlerExceptionResolver}, for example mapping certain exceptions to error pages.
  94  * Default are
  95  * {@link org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver},
  96  * {@link org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver}, and
  97  * {@link org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver}.
  98  * These HandlerExceptionResolvers can be overridden through the application context.
  99  * HandlerExceptionResolver can be given any bean name (they are tested by type).
 100  *
 101  * <li>Its view resolution strategy can be specified via a {@link ViewResolver}
 102  * implementation, resolving symbolic view names into View objects. Default is
 103  * {@link org.springframework.web.servlet.view.InternalResourceViewResolver}.
 104  * ViewResolver objects can be added as beans in the application context, overriding the
 105  * default ViewResolver. ViewResolvers can be given any bean name (they are tested by type).
 106  *
 107  * <li>If a {@link View} or view name is not supplied by the user, then the configured
 108  * {@link RequestToViewNameTranslator} will translate the current request into a view name.
 109  * The corresponding bean name is "viewNameTranslator"; the default is
 110  * {@link org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator}.
 111  *
 112  * <li>The dispatcher's strategy for resolving multipart requests is determined by a
 113  * {@link org.springframework.web.multipart.MultipartResolver} implementation.
 114  * Implementations for Apache Commons FileUpload and Servlet 3 are included; the typical
 115  * choice is {@link org.springframework.web.multipart.commons.CommonsMultipartResolver}.
 116  * The MultipartResolver bean name is "multipartResolver"; default is none.
 117  *
 118  * <li>Its locale resolution strategy is determined by a {@link LocaleResolver}.
 119  * Out-of-the-box implementations work via HTTP accept header, cookie, or session.
 120  * The LocaleResolver bean name is "localeResolver"; default is
 121  * {@link org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver}.
 122  *
 123  * <li>Its theme resolution strategy is determined by a {@link ThemeResolver}.
 124  * Implementations for a fixed theme and for cookie and session storage are included.
 125  * The ThemeResolver bean name is "themeResolver"; default is
 126  * {@link org.springframework.web.servlet.theme.FixedThemeResolver}.
 127  * </ul>
 128  *
 129  * <p><b>NOTE: The {@code @RequestMapping} annotation will only be processed if a
 130  * corresponding {@code HandlerMapping} (for type-level annotations) and/or
 131  * {@code HandlerAdapter} (for method-level annotations) is present in the dispatcher.</b>
 132  * This is the case by default. However, if you are defining custom {@code HandlerMappings}
 133  * or {@code HandlerAdapters}, then you need to make sure that a corresponding custom
 134  * {@code DefaultAnnotationHandlerMapping} and/or {@code AnnotationMethodHandlerAdapter}
 135  * is defined as well - provided that you intend to use {@code @RequestMapping}.
 136  *
 137  * <p><b>A web application can define any number of DispatcherServlets.</b>
 138  * Each servlet will operate in its own namespace, loading its own application context
 139  * with mappings, handlers, etc. Only the root application context as loaded by
 140  * {@link org.springframework.web.context.ContextLoaderListener}, if any, will be shared.
 141  *
 142  * <p>As of Spring 3.1, {@code DispatcherServlet} may now be injected with a web
 143  * application context, rather than creating its own internally. This is useful in Servlet
 144  * 3.0+ environments, which support programmatic registration of servlet instances.
 145  * See the {@link #DispatcherServlet(WebApplicationContext)} javadoc for details.
 146  *
 147  * @author Rod Johnson
 148  * @author Juergen Hoeller
 149  * @author Rob Harrop
 150  * @author Chris Beams
 151  * @author Rossen Stoyanchev
 152  * @see org.springframework.web.HttpRequestHandler
 153  * @see org.springframework.web.servlet.mvc.Controller
 154  * @see org.springframework.web.context.ContextLoaderListener
 155  */
 156 @SuppressWarnings("serial")
 157 public class DispatcherServlet extends FrameworkServlet {
 158 
 159     /** Well-known name for the MultipartResolver object in the bean factory for this namespace. */
 160     public static final String MULTIPART_RESOLVER_BEAN_NAME = "multipartResolver";
 161 
 162     /** Well-known name for the LocaleResolver object in the bean factory for this namespace. */
 163     public static final String LOCALE_RESOLVER_BEAN_NAME = "localeResolver";
 164 
 165     /** Well-known name for the ThemeResolver object in the bean factory for this namespace. */
 166     public static final String THEME_RESOLVER_BEAN_NAME = "themeResolver";
 167 
 168     /**
 169      * Well-known name for the HandlerMapping object in the bean factory for this namespace.
 170      * Only used when "detectAllHandlerMappings" is turned off.
 171      * @see #setDetectAllHandlerMappings
 172      */
 173     public static final String HANDLER_MAPPING_BEAN_NAME = "handlerMapping";
 174 
 175     /**
 176      * Well-known name for the HandlerAdapter object in the bean factory for this namespace.
 177      * Only used when "detectAllHandlerAdapters" is turned off.
 178      * @see #setDetectAllHandlerAdapters
 179      */
 180     public static final String HANDLER_ADAPTER_BEAN_NAME = "handlerAdapter";
 181 
 182     /**
 183      * Well-known name for the HandlerExceptionResolver object in the bean factory for this namespace.
 184      * Only used when "detectAllHandlerExceptionResolvers" is turned off.
 185      * @see #setDetectAllHandlerExceptionResolvers
 186      */
 187     public static final String HANDLER_EXCEPTION_RESOLVER_BEAN_NAME = "handlerExceptionResolver";
 188 
 189     /**
 190      * Well-known name for the RequestToViewNameTranslator object in the bean factory for this namespace.
 191      */
 192     public static final String REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME = "viewNameTranslator";
 193 
 194     /**
 195      * Well-known name for the ViewResolver object in the bean factory for this namespace.
 196      * Only used when "detectAllViewResolvers" is turned off.
 197      * @see #setDetectAllViewResolvers
 198      */
 199     public static final String VIEW_RESOLVER_BEAN_NAME = "viewResolver";
 200 
 201     /**
 202      * Well-known name for the FlashMapManager object in the bean factory for this namespace.
 203      */
 204     public static final String FLASH_MAP_MANAGER_BEAN_NAME = "flashMapManager";
 205 
 206     /**
 207      * Request attribute to hold the current web application context.
 208      * Otherwise only the global web app context is obtainable by tags etc.
 209      * @see org.springframework.web.servlet.support.RequestContextUtils#findWebApplicationContext
 210      */
 211     public static final String WEB_APPLICATION_CONTEXT_ATTRIBUTE = DispatcherServlet.class.getName() + ".CONTEXT";
 212 
 213     /**
 214      * Request attribute to hold the current LocaleResolver, retrievable by views.
 215      * @see org.springframework.web.servlet.support.RequestContextUtils#getLocaleResolver
 216      */
 217     public static final String LOCALE_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() + ".LOCALE_RESOLVER";
 218 
 219     /**
 220      * Request attribute to hold the current ThemeResolver, retrievable by views.
 221      * @see org.springframework.web.servlet.support.RequestContextUtils#getThemeResolver
 222      */
 223     public static final String THEME_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() + ".THEME_RESOLVER";
 224 
 225     /**
 226      * Request attribute to hold the current ThemeSource, retrievable by views.
 227      * @see org.springframework.web.servlet.support.RequestContextUtils#getThemeSource
 228      */
 229     public static final String THEME_SOURCE_ATTRIBUTE = DispatcherServlet.class.getName() + ".THEME_SOURCE";
 230 
 231     /**
 232      * Name of request attribute that holds a read-only {@code Map<String,?>}
 233      * with "input" flash attributes saved by a previous request, if any.
 234      * @see org.springframework.web.servlet.support.RequestContextUtils#getInputFlashMap(HttpServletRequest)
 235      */
 236     public static final String INPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() + ".INPUT_FLASH_MAP";
 237 
 238     /**
 239      * Name of request attribute that holds the "output" {@link FlashMap} with
 240      * attributes to save for a subsequent request.
 241      * @see org.springframework.web.servlet.support.RequestContextUtils#getOutputFlashMap(HttpServletRequest)
 242      */
 243     public static final String OUTPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() + ".OUTPUT_FLASH_MAP";
 244 
 245     /**
 246      * Name of request attribute that holds the {@link FlashMapManager}.
 247      * @see org.springframework.web.servlet.support.RequestContextUtils#getFlashMapManager(HttpServletRequest)
 248      */
 249     public static final String FLASH_MAP_MANAGER_ATTRIBUTE = DispatcherServlet.class.getName() + ".FLASH_MAP_MANAGER";
 250 
 251     /**
 252      * Name of request attribute that exposes an Exception resolved with an
 253      * {@link HandlerExceptionResolver} but where no view was rendered
 254      * (e.g. setting the status code).
 255      */
 256     public static final String EXCEPTION_ATTRIBUTE = DispatcherServlet.class.getName() + ".EXCEPTION";
 257 
 258     /** Log category to use when no mapped handler is found for a request. */
 259     public static final String PAGE_NOT_FOUND_LOG_CATEGORY = "org.springframework.web.servlet.PageNotFound";
 260 
 261     /**
 262      * Name of the class path resource (relative to the DispatcherServlet class)
 263      * that defines DispatcherServlet's default strategy names.
 264      */
 265     private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";
 266 
 267     /**
 268      * Common prefix that DispatcherServlet's default strategy attributes start with.
 269      */
 270     private static final String DEFAULT_STRATEGIES_PREFIX = "org.springframework.web.servlet";
 271 
 272     /** Additional logger to use when no mapped handler is found for a request. */
 273     protected static final Log pageNotFoundLogger = LogFactory.getLog(PAGE_NOT_FOUND_LOG_CATEGORY);
 274 
 275     private static final Properties defaultStrategies;
 276 
 277     static {
 278         // Load default strategy implementations from properties file.
 279         // This is currently strictly internal and not meant to be customized
 280         // by application developers.
 281         try {
 282             ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
 283             defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
 284         }
 285         catch (IOException ex) {
 286             throw new IllegalStateException("Could not load '" + DEFAULT_STRATEGIES_PATH + "': " + ex.getMessage());
 287         }
 288     }
 289 
 290     /** Detect all HandlerMappings or just expect "handlerMapping" bean? */
 291     private boolean detectAllHandlerMappings = true;
 292 
 293     /** Detect all HandlerAdapters or just expect "handlerAdapter" bean? */
 294     private boolean detectAllHandlerAdapters = true;
 295 
 296     /** Detect all HandlerExceptionResolvers or just expect "handlerExceptionResolver" bean? */
 297     private boolean detectAllHandlerExceptionResolvers = true;
 298 
 299     /** Detect all ViewResolvers or just expect "viewResolver" bean? */
 300     private boolean detectAllViewResolvers = true;
 301 
 302     /** Throw a NoHandlerFoundException if no Handler was found to process this request? **/
 303     private boolean throwExceptionIfNoHandlerFound = false;
 304 
 305     /** Perform cleanup of request attributes after include request? */
 306     private boolean cleanupAfterInclude = true;
 307 
 308     /** MultipartResolver used by this servlet */
 309     private MultipartResolver multipartResolver;
 310 
 311     /** LocaleResolver used by this servlet */
 312     private LocaleResolver localeResolver;
 313 
 314     /** ThemeResolver used by this servlet */
 315     private ThemeResolver themeResolver;
 316 
 317     /** List of HandlerMappings used by this servlet */
 318     private List<HandlerMapping> handlerMappings;
 319 
 320     /** List of HandlerAdapters used by this servlet */
 321     private List<HandlerAdapter> handlerAdapters;
 322 
 323     /** List of HandlerExceptionResolvers used by this servlet */
 324     private List<HandlerExceptionResolver> handlerExceptionResolvers;
 325 
 326     /** RequestToViewNameTranslator used by this servlet */
 327     private RequestToViewNameTranslator viewNameTranslator;
 328 
 329     /** FlashMapManager used by this servlet */
 330     private FlashMapManager flashMapManager;
 331 
 332     /** List of ViewResolvers used by this servlet */
 333     private List<ViewResolver> viewResolvers;
 334 
 335 
 336     /**
 337      * Create a new {@code DispatcherServlet} that will create its own internal web
 338      * application context based on defaults and values provided through servlet
 339      * init-params. Typically used in Servlet 2.5 or earlier environments, where the only
 340      * option for servlet registration is through {@code web.xml} which requires the use
 341      * of a no-arg constructor.
 342      * <p>Calling {@link #setContextConfigLocation} (init-param 'contextConfigLocation')
 343      * will dictate which XML files will be loaded by the
 344      * {@linkplain #DEFAULT_CONTEXT_CLASS default XmlWebApplicationContext}
 345      * <p>Calling {@link #setContextClass} (init-param 'contextClass') overrides the
 346      * default {@code XmlWebApplicationContext} and allows for specifying an alternative class,
 347      * such as {@code AnnotationConfigWebApplicationContext}.
 348      * <p>Calling {@link #setContextInitializerClasses} (init-param 'contextInitializerClasses')
 349      * indicates which {@code ApplicationContextInitializer} classes should be used to
 350      * further configure the internal application context prior to refresh().
 351      * @see #DispatcherServlet(WebApplicationContext)
 352      */
 353     public DispatcherServlet() {
 354         super();
 355         setDispatchOptionsRequest(true);
 356     }
 357 
 358     /**
 359      * Create a new {@code DispatcherServlet} with the given web application context. This
 360      * constructor is useful in Servlet 3.0+ environments where instance-based registration
 361      * of servlets is possible through the {@link ServletContext#addServlet} API.
 362      * <p>Using this constructor indicates that the following properties / init-params
 363      * will be ignored:
 364      * <ul>
 365      * <li>{@link #setContextClass(Class)} / 'contextClass'</li>
 366      * <li>{@link #setContextConfigLocation(String)} / 'contextConfigLocation'</li>
 367      * <li>{@link #setContextAttribute(String)} / 'contextAttribute'</li>
 368      * <li>{@link #setNamespace(String)} / 'namespace'</li>
 369      * </ul>
 370      * <p>The given web application context may or may not yet be {@linkplain
 371      * ConfigurableApplicationContext#refresh() refreshed}. If it has <strong>not</strong>
 372      * already been refreshed (the recommended approach), then the following will occur:
 373      * <ul>
 374      * <li>If the given context does not already have a {@linkplain
 375      * ConfigurableApplicationContext#setParent parent}, the root application context
 376      * will be set as the parent.</li>
 377      * <li>If the given context has not already been assigned an {@linkplain
 378      * ConfigurableApplicationContext#setId id}, one will be assigned to it</li>
 379      * <li>{@code ServletContext} and {@code ServletConfig} objects will be delegated to
 380      * the application context</li>
 381      * <li>{@link #postProcessWebApplicationContext} will be called</li>
 382      * <li>Any {@code ApplicationContextInitializer}s specified through the
 383      * "contextInitializerClasses" init-param or through the {@link
 384      * #setContextInitializers} property will be applied.</li>
 385      * <li>{@link ConfigurableApplicationContext#refresh refresh()} will be called if the
 386      * context implements {@link ConfigurableApplicationContext}</li>
 387      * </ul>
 388      * If the context has already been refreshed, none of the above will occur, under the
 389      * assumption that the user has performed these actions (or not) per their specific
 390      * needs.
 391      * <p>See {@link org.springframework.web.WebApplicationInitializer} for usage examples.
 392      * @param webApplicationContext the context to use
 393      * @see #initWebApplicationContext
 394      * @see #configureAndRefreshWebApplicationContext
 395      * @see org.springframework.web.WebApplicationInitializer
 396      */
 397     public DispatcherServlet(WebApplicationContext webApplicationContext) {
 398         super(webApplicationContext);
 399         setDispatchOptionsRequest(true);
 400     }
 401 
 402 
 403     /**
 404      * Set whether to detect all HandlerMapping beans in this servlet's context. Otherwise,
 405      * just a single bean with name "handlerMapping" will be expected.
 406      * <p>Default is "true". Turn this off if you want this servlet to use a single
 407      * HandlerMapping, despite multiple HandlerMapping beans being defined in the context.
 408      */
 409     public void setDetectAllHandlerMappings(boolean detectAllHandlerMappings) {
 410         this.detectAllHandlerMappings = detectAllHandlerMappings;
 411     }
 412 
 413     /**
 414      * Set whether to detect all HandlerAdapter beans in this servlet's context. Otherwise,
 415      * just a single bean with name "handlerAdapter" will be expected.
 416      * <p>Default is "true". Turn this off if you want this servlet to use a single
 417      * HandlerAdapter, despite multiple HandlerAdapter beans being defined in the context.
 418      */
 419     public void setDetectAllHandlerAdapters(boolean detectAllHandlerAdapters) {
 420         this.detectAllHandlerAdapters = detectAllHandlerAdapters;
 421     }
 422 
 423     /**
 424      * Set whether to detect all HandlerExceptionResolver beans in this servlet's context. Otherwise,
 425      * just a single bean with name "handlerExceptionResolver" will be expected.
 426      * <p>Default is "true". Turn this off if you want this servlet to use a single
 427      * HandlerExceptionResolver, despite multiple HandlerExceptionResolver beans being defined in the context.
 428      */
 429     public void setDetectAllHandlerExceptionResolvers(boolean detectAllHandlerExceptionResolvers) {
 430         this.detectAllHandlerExceptionResolvers = detectAllHandlerExceptionResolvers;
 431     }
 432 
 433     /**
 434      * Set whether to detect all ViewResolver beans in this servlet's context. Otherwise,
 435      * just a single bean with name "viewResolver" will be expected.
 436      * <p>Default is "true". Turn this off if you want this servlet to use a single
 437      * ViewResolver, despite multiple ViewResolver beans being defined in the context.
 438      */
 439     public void setDetectAllViewResolvers(boolean detectAllViewResolvers) {
 440         this.detectAllViewResolvers = detectAllViewResolvers;
 441     }
 442 
 443     /**
 444      * Set whether to throw a NoHandlerFoundException when no Handler was found for this request.
 445      * This exception can then be caught with a HandlerExceptionResolver or an
 446      * {@code @ExceptionHandler} controller method.
 447      * <p>Note that if {@link org.springframework.web.servlet.resource.DefaultServletHttpRequestHandler}
 448      * is used, then requests will always be forwarded to the default servlet and a
 449      * NoHandlerFoundException would never be thrown in that case.
 450      * <p>Default is "false", meaning the DispatcherServlet sends a NOT_FOUND error through the
 451      * Servlet response.
 452      * @since 4.0
 453      */
 454     public void setThrowExceptionIfNoHandlerFound(boolean throwExceptionIfNoHandlerFound) {
 455         this.throwExceptionIfNoHandlerFound = throwExceptionIfNoHandlerFound;
 456     }
 457 
 458     /**
 459      * Set whether to perform cleanup of request attributes after an include request, that is,
 460      * whether to reset the original state of all request attributes after the DispatcherServlet
 461      * has processed within an include request. Otherwise, just the DispatcherServlet's own
 462      * request attributes will be reset, but not model attributes for JSPs or special attributes
 463      * set by views (for example, JSTL's).
 464      * <p>Default is "true", which is strongly recommended. Views should not rely on request attributes
 465      * having been set by (dynamic) includes. This allows JSP views rendered by an included controller
 466      * to use any model attributes, even with the same names as in the main JSP, without causing side
 467      * effects. Only turn this off for special needs, for example to deliberately allow main JSPs to
 468      * access attributes from JSP views rendered by an included controller.
 469      */
 470     public void setCleanupAfterInclude(boolean cleanupAfterInclude) {
 471         this.cleanupAfterInclude = cleanupAfterInclude;
 472     }
 473 
 474 
 475     /**
 476      * This implementation calls {@link #initStrategies}.
 477      */
 478     @Override
 479     protected void onRefresh(ApplicationContext context) {
 480         initStrategies(context);
 481     }
 482 
 483     /**
 484      * Initialize the strategy objects that this servlet uses.
 485      * <p>May be overridden in subclasses in order to initialize further strategy objects.
 486      */
 487     protected void initStrategies(ApplicationContext context) {
 488         initMultipartResolver(context);
 489         initLocaleResolver(context);
 490         initThemeResolver(context);
 491         initHandlerMappings(context);
 492         initHandlerAdapters(context);
 493         initHandlerExceptionResolvers(context);
 494         initRequestToViewNameTranslator(context);
 495         initViewResolvers(context);
 496         initFlashMapManager(context);
 497     }
 498 
 499     /**
 500      * Initialize the MultipartResolver used by this class.
 501      * <p>If no bean is defined with the given name in the BeanFactory for this namespace,
 502      * no multipart handling is provided.
 503      */
 504     private void initMultipartResolver(ApplicationContext context) {
 505         try {
 506             this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);
 507             if (logger.isDebugEnabled()) {
 508                 logger.debug("Using MultipartResolver [" + this.multipartResolver + "]");
 509             }
 510         }
 511         catch (NoSuchBeanDefinitionException ex) {
 512             // Default is no multipart resolver.
 513             this.multipartResolver = null;
 514             if (logger.isDebugEnabled()) {
 515                 logger.debug("Unable to locate MultipartResolver with name '" + MULTIPART_RESOLVER_BEAN_NAME +
 516                         "': no multipart request handling provided");
 517             }
 518         }
 519     }
 520 
 521     /**
 522      * Initialize the LocaleResolver used by this class.
 523      * <p>If no bean is defined with the given name in the BeanFactory for this namespace,
 524      * we default to AcceptHeaderLocaleResolver.
 525      */
 526     private void initLocaleResolver(ApplicationContext context) {
 527         try {
 528             this.localeResolver = context.getBean(LOCALE_RESOLVER_BEAN_NAME, LocaleResolver.class);
 529             if (logger.isDebugEnabled()) {
 530                 logger.debug("Using LocaleResolver [" + this.localeResolver + "]");
 531             }
 532         }
 533         catch (NoSuchBeanDefinitionException ex) {
 534             // We need to use the default.
 535             this.localeResolver = getDefaultStrategy(context, LocaleResolver.class);
 536             if (logger.isDebugEnabled()) {
 537                 logger.debug("Unable to locate LocaleResolver with name '" + LOCALE_RESOLVER_BEAN_NAME +
 538                         "': using default [" + this.localeResolver + "]");
 539             }
 540         }
 541     }
 542 
 543     /**
 544      * Initialize the ThemeResolver used by this class.
 545      * <p>If no bean is defined with the given name in the BeanFactory for this namespace,
 546      * we default to a FixedThemeResolver.
 547      */
 548     private void initThemeResolver(ApplicationContext context) {
 549         try {
 550             this.themeResolver = context.getBean(THEME_RESOLVER_BEAN_NAME, ThemeResolver.class);
 551             if (logger.isDebugEnabled()) {
 552                 logger.debug("Using ThemeResolver [" + this.themeResolver + "]");
 553             }
 554         }
 555         catch (NoSuchBeanDefinitionException ex) {
 556             // We need to use the default.
 557             this.themeResolver = getDefaultStrategy(context, ThemeResolver.class);
 558             if (logger.isDebugEnabled()) {
 559                 logger.debug("Unable to locate ThemeResolver with name '" + THEME_RESOLVER_BEAN_NAME +
 560                         "': using default [" + this.themeResolver + "]");
 561             }
 562         }
 563     }
 564 
 565     /**
 566      * Initialize the HandlerMappings used by this class.
 567      * <p>If no HandlerMapping beans are defined in the BeanFactory for this namespace,
 568      * we default to BeanNameUrlHandlerMapping.
 569      */
 570     private void initHandlerMappings(ApplicationContext context) {
 571         this.handlerMappings = null;
 572 
 573         if (this.detectAllHandlerMappings) {
 574             // Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
 575             Map<String, HandlerMapping> matchingBeans =
 576                     BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
 577             if (!matchingBeans.isEmpty()) {
 578                 this.handlerMappings = new ArrayList<HandlerMapping>(matchingBeans.values());
 579                 // We keep HandlerMappings in sorted order.
 580                 AnnotationAwareOrderComparator.sort(this.handlerMappings);
 581             }
 582         }
 583         else {
 584             try {
 585                 HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
 586                 this.handlerMappings = Collections.singletonList(hm);
 587             }
 588             catch (NoSuchBeanDefinitionException ex) {
 589                 // Ignore, we'll add a default HandlerMapping later.
 590             }
 591         }
 592 
 593         // Ensure we have at least one HandlerMapping, by registering
 594         // a default HandlerMapping if no other mappings are found.
 595         if (this.handlerMappings == null) {
 596             this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
 597             if (logger.isDebugEnabled()) {
 598                 logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
 599             }
 600         }
 601     }
 602 
 603     /**
 604      * Initialize the HandlerAdapters used by this class.
 605      * <p>If no HandlerAdapter beans are defined in the BeanFactory for this namespace,
 606      * we default to SimpleControllerHandlerAdapter.
 607      */
 608     private void initHandlerAdapters(ApplicationContext context) {
 609         this.handlerAdapters = null;
 610 
 611         if (this.detectAllHandlerAdapters) {
 612             // Find all HandlerAdapters in the ApplicationContext, including ancestor contexts.
 613             Map<String, HandlerAdapter> matchingBeans =
 614                     BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
 615             if (!matchingBeans.isEmpty()) {
 616                 this.handlerAdapters = new ArrayList<HandlerAdapter>(matchingBeans.values());
 617                 // We keep HandlerAdapters in sorted order.
 618                 AnnotationAwareOrderComparator.sort(this.handlerAdapters);
 619             }
 620         }
 621         else {
 622             try {
 623                 HandlerAdapter ha = context.getBean(HANDLER_ADAPTER_BEAN_NAME, HandlerAdapter.class);
 624                 this.handlerAdapters = Collections.singletonList(ha);
 625             }
 626             catch (NoSuchBeanDefinitionException ex) {
 627                 // Ignore, we'll add a default HandlerAdapter later.
 628             }
 629         }
 630 
 631         // Ensure we have at least some HandlerAdapters, by registering
 632         // default HandlerAdapters if no other adapters are found.
 633         if (this.handlerAdapters == null) {
 634             this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);
 635             if (logger.isDebugEnabled()) {
 636                 logger.debug("No HandlerAdapters found in servlet '" + getServletName() + "': using default");
 637             }
 638         }
 639     }
 640 
 641     /**
 642      * Initialize the HandlerExceptionResolver used by this class.
 643      * <p>If no bean is defined with the given name in the BeanFactory for this namespace,
 644      * we default to no exception resolver.
 645      */
 646     private void initHandlerExceptionResolvers(ApplicationContext context) {
 647         this.handlerExceptionResolvers = null;
 648 
 649         if (this.detectAllHandlerExceptionResolvers) {
 650             // Find all HandlerExceptionResolvers in the ApplicationContext, including ancestor contexts.
 651             Map<String, HandlerExceptionResolver> matchingBeans = BeanFactoryUtils
 652                     .beansOfTypeIncludingAncestors(context, HandlerExceptionResolver.class, true, false);
 653             if (!matchingBeans.isEmpty()) {
 654                 this.handlerExceptionResolvers = new ArrayList<HandlerExceptionResolver>(matchingBeans.values());
 655                 // We keep HandlerExceptionResolvers in sorted order.
 656                 AnnotationAwareOrderComparator.sort(this.handlerExceptionResolvers);
 657             }
 658         }
 659         else {
 660             try {
 661                 HandlerExceptionResolver her =
 662                         context.getBean(HANDLER_EXCEPTION_RESOLVER_BEAN_NAME, HandlerExceptionResolver.class);
 663                 this.handlerExceptionResolvers = Collections.singletonList(her);
 664             }
 665             catch (NoSuchBeanDefinitionException ex) {
 666                 // Ignore, no HandlerExceptionResolver is fine too.
 667             }
 668         }
 669 
 670         // Ensure we have at least some HandlerExceptionResolvers, by registering
 671         // default HandlerExceptionResolvers if no other resolvers are found.
 672         if (this.handlerExceptionResolvers == null) {
 673             this.handlerExceptionResolvers = getDefaultStrategies(context, HandlerExceptionResolver.class);
 674             if (logger.isDebugEnabled()) {
 675                 logger.debug("No HandlerExceptionResolvers found in servlet '" + getServletName() + "': using default");
 676             }
 677         }
 678     }
 679 
 680     /**
 681      * Initialize the RequestToViewNameTranslator used by this servlet instance.
 682      * <p>If no implementation is configured then we default to DefaultRequestToViewNameTranslator.
 683      */
 684     private void initRequestToViewNameTranslator(ApplicationContext context) {
 685         try {
 686             this.viewNameTranslator =
 687                     context.getBean(REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME, RequestToViewNameTranslator.class);
 688             if (logger.isDebugEnabled()) {
 689                 logger.debug("Using RequestToViewNameTranslator [" + this.viewNameTranslator + "]");
 690             }
 691         }
 692         catch (NoSuchBeanDefinitionException ex) {
 693             // We need to use the default.
 694             this.viewNameTranslator = getDefaultStrategy(context, RequestToViewNameTranslator.class);
 695             if (logger.isDebugEnabled()) {
 696                 logger.debug("Unable to locate RequestToViewNameTranslator with name '" +
 697                         REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME + "': using default [" + this.viewNameTranslator +
 698                         "]");
 699             }
 700         }
 701     }
 702 
 703     /**
 704      * Initialize the ViewResolvers used by this class.
 705      * <p>If no ViewResolver beans are defined in the BeanFactory for this
 706      * namespace, we default to InternalResourceViewResolver.
 707      * 通过该类初始化ViewResolvers，若BeanFactory里面未定义ViewResolver的beans，
 708      * 则默认使用InternalResourceViewResolver。
 709      */
 710     private void initViewResolvers(ApplicationContext context) {
 711         //初始化viewResolvers
 712         this.viewResolvers = null;
 713         //查找ApplicationContext（包括祖先上下文）中所有的ViewResolvers
 714         if (this.detectAllViewResolvers) {
 715             // Find all ViewResolvers in the ApplicationContext, including ancestor contexts.
 716             Map<String, ViewResolver> matchingBeans =
 717                     BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false);
 718             //若ViewResolvers存在，则将其放入ArrayList中并进行排序操作
 719             if (!matchingBeans.isEmpty()) {
 720                 this.viewResolvers = new ArrayList<ViewResolver>(matchingBeans.values());
 721                 // We keep ViewResolvers in sorted order.
 722                 AnnotationAwareOrderComparator.sort(this.viewResolvers);
 723             }
 724         }
 725         else {   //若ApplicationContext（包括祖先上下文）中没有ViewResolvers，则使用viewResolver
 726             try {
 727                 ViewResolver vr = context.getBean(VIEW_RESOLVER_BEAN_NAME, ViewResolver.class);
 728                 this.viewResolvers = Collections.singletonList(vr);
 729             }
 730             catch (NoSuchBeanDefinitionException ex) {
 731                 // Ignore, we'll add a default ViewResolver later.
 732             }
 733         }
 734         // Ensure we have at least one ViewResolver, by registering
 735         // a default ViewResolver if no other resolvers are found.
 736         //确保至少有一个ViewResolver，若果没有resolvers查到的话就注册一个默认的ViewResolver
 737         if (this.viewResolvers == null) {
 738             this.viewResolvers = getDefaultStrategies(context, ViewResolver.class);
 739             if (logger.isDebugEnabled()) {
 740                 logger.debug("No ViewResolvers found in servlet '" + getServletName() + "': using default");
 741             }
 742         }
 743     }
 744 
 745     /**
 746      * Initialize the {@link FlashMapManager} used by this servlet instance.
 747      * <p>If no implementation is configured then we default to
 748      * {@code org.springframework.web.servlet.support.DefaultFlashMapManager}.
 749      */
 750     private void initFlashMapManager(ApplicationContext context) {
 751         try {
 752             this.flashMapManager = context.getBean(FLASH_MAP_MANAGER_BEAN_NAME, FlashMapManager.class);
 753             if (logger.isDebugEnabled()) {
 754                 logger.debug("Using FlashMapManager [" + this.flashMapManager + "]");
 755             }
 756         }
 757         catch (NoSuchBeanDefinitionException ex) {
 758             // We need to use the default.
 759             this.flashMapManager = getDefaultStrategy(context, FlashMapManager.class);
 760             if (logger.isDebugEnabled()) {
 761                 logger.debug("Unable to locate FlashMapManager with name '" +
 762                         FLASH_MAP_MANAGER_BEAN_NAME + "': using default [" + this.flashMapManager + "]");
 763             }
 764         }
 765     }
 766 
 767     /**
 768      * Return this servlet's ThemeSource, if any; else return {@code null}.
 769      * <p>Default is to return the WebApplicationContext as ThemeSource,
 770      * provided that it implements the ThemeSource interface.
 771      * @return the ThemeSource, if any
 772      * @see #getWebApplicationContext()
 773      */
 774     public final ThemeSource getThemeSource() {
 775         if (getWebApplicationContext() instanceof ThemeSource) {
 776             return (ThemeSource) getWebApplicationContext();
 777         }
 778         else {
 779             return null;
 780         }
 781     }
 782 
 783     /**
 784      * Obtain this servlet's MultipartResolver, if any.
 785      * @return the MultipartResolver used by this servlet, or {@code null} if none
 786      * (indicating that no multipart support is available)
 787      */
 788     public final MultipartResolver getMultipartResolver() {
 789         return this.multipartResolver;
 790     }
 791 
 792     /**
 793      * Return the default strategy object for the given strategy interface.
 794      * <p>The default implementation delegates to {@link #getDefaultStrategies},
 795      * expecting a single object in the list.
 796      * @param context the current WebApplicationContext
 797      * @param strategyInterface the strategy interface
 798      * @return the corresponding strategy object
 799      * @see #getDefaultStrategies
 800      */
 801     protected <T> T getDefaultStrategy(ApplicationContext context, Class<T> strategyInterface) {
 802         List<T> strategies = getDefaultStrategies(context, strategyInterface);
 803         if (strategies.size() != 1) {
 804             throw new BeanInitializationException(
 805                     "DispatcherServlet needs exactly 1 strategy for interface [" + strategyInterface.getName() + "]");
 806         }
 807         return strategies.get(0);
 808     }
 809 
 810     /**
 811      * Create a List of default strategy objects for the given strategy interface.
 812      * <p>The default implementation uses the "DispatcherServlet.properties" file (in the same
 813      * package as the DispatcherServlet class) to determine the class names. It instantiates
 814      * the strategy objects through the context's BeanFactory.
 815      * @param context the current WebApplicationContext
 816      * @param strategyInterface the strategy interface
 817      * @return the List of corresponding strategy objects
 818      */
 819     @SuppressWarnings("unchecked")
 820     protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
 821         String key = strategyInterface.getName();
 822         String value = defaultStrategies.getProperty(key);
 823         if (value != null) {
 824             String[] classNames = StringUtils.commaDelimitedListToStringArray(value);
 825             List<T> strategies = new ArrayList<T>(classNames.length);
 826             for (String className : classNames) {
 827                 try {
 828                     Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());
 829                     Object strategy = createDefaultStrategy(context, clazz);
 830                     strategies.add((T) strategy);
 831                 }
 832                 catch (ClassNotFoundException ex) {
 833                     throw new BeanInitializationException(
 834                             "Could not find DispatcherServlet's default strategy class [" + className +
 835                                     "] for interface [" + key + "]", ex);
 836                 }
 837                 catch (LinkageError err) {
 838                     throw new BeanInitializationException(
 839                             "Error loading DispatcherServlet's default strategy class [" + className +
 840                                     "] for interface [" + key + "]: problem with class file or dependent class", err);
 841                 }
 842             }
 843             return strategies;
 844         }
 845         else {
 846             return new LinkedList<T>();
 847         }
 848     }
 849 
 850     /**
 851      * Create a default strategy.
 852      * <p>The default implementation uses
 853      * {@link org.springframework.beans.factory.config.AutowireCapableBeanFactory#createBean}.
 854      * @param context the current WebApplicationContext
 855      * @param clazz the strategy implementation class to instantiate
 856      * @return the fully configured strategy instance
 857      * @see org.springframework.context.ApplicationContext#getAutowireCapableBeanFactory()
 858      * @see org.springframework.beans.factory.config.AutowireCapableBeanFactory#createBean
 859      */
 860     protected Object createDefaultStrategy(ApplicationContext context, Class<?> clazz) {
 861         return context.getAutowireCapableBeanFactory().createBean(clazz);
 862     }
 863 
 864 
 865     /**
 866      * Exposes the DispatcherServlet-specific request attributes and delegates to {@link #doDispatch}
 867      * for the actual dispatching.
 868      */
 869     @Override
 870     protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
 871         if (logger.isDebugEnabled()) {
 872             String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
 873             logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +
 874                     " processing " + request.getMethod() + " request for [" + getRequestUri(request) + "]");
 875         }
 876 
 877         // Keep a snapshot of the request attributes in case of an include,
 878         // to be able to restore the original attributes after the include.
 879         Map<String, Object> attributesSnapshot = null;
 880         if (WebUtils.isIncludeRequest(request)) {
 881             attributesSnapshot = new HashMap<String, Object>();
 882             Enumeration<?> attrNames = request.getAttributeNames();
 883             while (attrNames.hasMoreElements()) {
 884                 String attrName = (String) attrNames.nextElement();
 885                 if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
 886                     attributesSnapshot.put(attrName, request.getAttribute(attrName));
 887                 }
 888             }
 889         }
 890 
 891         // Make framework objects available to handlers and view objects.
 892         request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
 893         request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
 894         request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
 895         request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());
 896 
 897         FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
 898         if (inputFlashMap != null) {
 899             request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
 900         }
 901         request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
 902         request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
 903 
 904         try {
 905             doDispatch(request, response);
 906         }
 907         finally {
 908             if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
 909                 // Restore the original attribute snapshot, in case of an include.
 910                 if (attributesSnapshot != null) {
 911                     restoreAttributesAfterInclude(request, attributesSnapshot);
 912                 }
 913             }
 914         }
 915     }
 916 
 917     /**
 918      * Process the actual dispatching to the handler.
 919      * <p>The handler will be obtained by applying the servlet's HandlerMappings in order.
 920      * The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters
 921      * to find the first that supports the handler class.
 922      * <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers
 923      * themselves to decide which methods are acceptable.
 924      * 处理分发请求。处理程序将通过应用servlet的HandlerMappings来获得。HandlerAdapter将通过查询servlet
 925      * 安装的HandlerAdapter获得。所有的HTTP方法都被该方法处理。这取决于handleradapter或handler。
 926      * 自己决定哪些方法是可以接受的。
 927      * @param request current HTTP request
 928      * @param response current HTTP response
 929      * @throws Exception in case of any kind of processing failure
 930      */
 931     protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
 932         HttpServletRequest processedRequest = request;//获取请求
 933         HandlerExecutionChain mappedHandler = null;//初始化Hadler处理链
 934         boolean multipartRequestParsed = false;
 935         //实例化web异步管理类
 936         WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
 937 
 938         try {
 939             ModelAndView mv = null;//初始化ModelAndView
 940             Exception dispatchException = null;//初始化分发异常
 941 
 942             try {
 943                 processedRequest = checkMultipart(request);
 944                 multipartRequestParsed = (processedRequest != request);
 945 
 946                 // Determine handler for the current request.确定当前请求的处理程序
 947                 mappedHandler = getHandler(processedRequest);
 948                 if (mappedHandler == null || mappedHandler.getHandler() == null) {
 949                     noHandlerFound(processedRequest, response);
 950                     return;
 951                 }
 952 
 953                 // Determine handler adapter for the current request.确定当前请求的处理程序适配器
 954                 HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
 955 
 956                 // Process last-modified header, if supported by the handler.
 957                 String method = request.getMethod();
 958                 boolean isGet = "GET".equals(method);
 959                 if (isGet || "HEAD".equals(method)) {
 960                     long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
 961                     if (logger.isDebugEnabled()) {
 962                         logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
 963                     }
 964                     if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
 965                         return;
 966                     }
 967                 }
 968 
 969                 if (!mappedHandler.applyPreHandle(processedRequest, response)) {
 970                     return;
 971                 }
 972 
 973                 // Actually invoke the handler.实际调用处理程序。
 974                 mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
 975                 //当前请求对应的handler选择使用异步的方式处理当前请求
 976                 if (asyncManager.isConcurrentHandlingStarted()) {
 977                     return;
 978                 }
 979 
 980                 applyDefaultViewName(processedRequest, mv);
 981                 mappedHandler.applyPostHandle(processedRequest, response, mv);
 982             }
 983             catch (Exception ex) {
 984                 dispatchException = ex;
 985             }
 986             catch (Throwable err) {
 987                 // As of 4.3, we're processing Errors thrown from handler methods as well,
 988                 // making them available for @ExceptionHandler methods and other scenarios.
 989                 dispatchException = new NestedServletException("Handler dispatch failed", err);
 990             }
 991             processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
 992         }
 993         catch (Exception ex) {
 994             triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
 995         }
 996         catch (Throwable err) {
 997             triggerAfterCompletion(processedRequest, response, mappedHandler,
 998                     new NestedServletException("Handler processing failed", err));
 999         }
1000         finally {
1001             if (asyncManager.isConcurrentHandlingStarted()) {
1002                 // Instead of postHandle and afterCompletion
1003                 if (mappedHandler != null) {
1004                     mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
1005                 }
1006             }
1007             else {
1008                 // Clean up any resources used by a multipart request.清理文件上传用到的任何资源
1009                 if (multipartRequestParsed) {
1010                     cleanupMultipart(processedRequest);
1011                 }
1012             }
1013         }
1014     }
1015 
1016     /**
1017      * Do we need view name translation?
1018      */
1019     private void applyDefaultViewName(HttpServletRequest request, ModelAndView mv) throws Exception {
1020         if (mv != null && !mv.hasView()) {
1021             mv.setViewName(getDefaultViewName(request));
1022         }
1023     }
1024 
1025     /**
1026      * Handle the result of handler selection and handler invocation, which is
1027      * either a ModelAndView or an Exception to be resolved to a ModelAndView.
1028      * 处理选择的handler或者回调的handler的结果，要么是一个ModelAndView，要么是一个异常。
1029      */
1030     private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
1031             HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {
1032 
1033         boolean errorView = false;
1034         //若发生了异常，根据异常的类型做不同处理
1035         if (exception != null) {
1036             if (exception instanceof ModelAndViewDefiningException) {
1037                 logger.debug("ModelAndViewDefiningException encountered", exception);
1038                 mv = ((ModelAndViewDefiningException) exception).getModelAndView();
1039             }
1040             else {
1041                 Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
1042                 mv = processHandlerException(request, response, handler, exception);
1043                 errorView = (mv != null);
1044             }
1045         }
1046 
1047         // Did the handler return a view to render?
1048         //判断handler是否返回了用于渲染的视图
1049         if (mv != null && !mv.wasCleared()) {
1050             render(mv, request, response);//渲染给定的ModelAndView
1051             if (errorView) {
1052                 WebUtils.clearErrorRequestAttributes(request);
1053             }
1054         }
1055         else {  //无ModelAndView返回
1056             if (logger.isDebugEnabled()) {
1057                 logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
1058                         "': assuming HandlerAdapter completed request handling");
1059             }
1060         }
1061         //若handler以异步方式处理请求，则返回
1062         if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
1063             // Concurrent handling started during a forward
1064             return;
1065         }
1066         //handler执行链不为空，则在完成后触发映射的handler拦截器
1067         if (mappedHandler != null) {
1068             mappedHandler.triggerAfterCompletion(request, response, null);
1069         }
1070     }
1071 
1072     /**
1073      * Build a LocaleContext for the given request, exposing the request's primary locale as current locale.
1074      * <p>The default implementation uses the dispatcher's LocaleResolver to obtain the current locale,
1075      * which might change during a request.
1076      * @param request current HTTP request
1077      * @return the corresponding LocaleContext
1078      */
1079     @Override
1080     protected LocaleContext buildLocaleContext(final HttpServletRequest request) {
1081         if (this.localeResolver instanceof LocaleContextResolver) {
1082             return ((LocaleContextResolver) this.localeResolver).resolveLocaleContext(request);
1083         }
1084         else {
1085             return new LocaleContext() {
1086                 @Override
1087                 public Locale getLocale() {
1088                     return localeResolver.resolveLocale(request);
1089                 }
1090             };
1091         }
1092     }
1093 
1094     /**
1095      * Convert the request into a multipart request, and make multipart resolver available.
1096      * <p>If no multipart resolver is set, simply use the existing request.
1097      * 将请求转成文件上传请求并且可以获取文件上传解析器
1098      * 如果没有设置文件上传解析器，那就使用已存在的请求。
1099      * @param request current HTTP request
1100      * @return the processed request (multipart wrapper if necessary)
1101      * @see MultipartResolver#resolveMultipart
1102      */
1103     protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
1104         //存在multipartResolver并且是multipart请求
1105         if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) {
1106             if (WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class) != null) {
1107                 logger.debug("Request is already a MultipartHttpServletRequest - if not in a forward, " +
1108                         "this typically results from an additional MultipartFilter in web.xml");
1109             }
1110             else if (hasMultipartException(request) ) {
1111                 logger.debug("Multipart resolution failed for current request before - " +
1112                         "skipping re-resolution for undisturbed error rendering");
1113             }
1114             else {
1115                 try {
1116                     return this.multipartResolver.resolveMultipart(request);
1117                 }
1118                 catch (MultipartException ex) {
1119                     if (request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) != null) {
1120                         logger.debug("Multipart resolution failed for error dispatch", ex);
1121                         // Keep processing error dispatch with regular request handle below
1122                     }
1123                     else {
1124                         throw ex;
1125                     }
1126                 }
1127             }
1128         }
1129         // If not returned before: return original request.
1130         return request;
1131     }
1132 
1133     /**
1134      * Check "javax.servlet.error.exception" attribute for a multipart exception.
1135      * 检查是否有MultipartException
1136      */
1137     private boolean hasMultipartException(HttpServletRequest request) {
1138         Throwable error = (Throwable) request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE);
1139         while (error != null) {
1140             if (error instanceof MultipartException) {
1141                 return true;
1142             }
1143             error = error.getCause();
1144         }
1145         return false;
1146     }
1147 
1148     /**
1149      * Clean up any resources used by the given multipart request (if any).
1150      * @param request current HTTP request
1151      * @see MultipartResolver#cleanupMultipart
1152      */
1153     protected void cleanupMultipart(HttpServletRequest request) {
1154         MultipartHttpServletRequest multipartRequest =
1155                 WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class);
1156         if (multipartRequest != null) {
1157             this.multipartResolver.cleanupMultipart(multipartRequest);
1158         }
1159     }
1160 
1161     /**
1162      * Return the HandlerExecutionChain for this request.
1163      * 返回请求对应的handler执行链
1164      * <p>Tries all handler mappings in order.
1165      * @param request current HTTP request
1166      * @return the HandlerExecutionChain, or {@code null} if no handler could be found
1167      */
1168     protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
1169         for (HandlerMapping hm : this.handlerMappings) {
1170             if (logger.isTraceEnabled()) {
1171                 logger.trace(
1172                         "Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
1173             }
1174             HandlerExecutionChain handler = hm.getHandler(request);
1175             if (handler != null) {
1176                 return handler;
1177             }
1178         }
1179         return null;
1180     }
1181 
1182     /**
1183      * No handler found -> set appropriate HTTP response status.
1184      * @param request current HTTP request
1185      * @param response current HTTP response
1186      * @throws Exception if preparing the response failed
1187      */
1188     protected void noHandlerFound(HttpServletRequest request, HttpServletResponse response) throws Exception {
1189         if (pageNotFoundLogger.isWarnEnabled()) {
1190             pageNotFoundLogger.warn("No mapping found for HTTP request with URI [" + getRequestUri(request) +
1191                     "] in DispatcherServlet with name '" + getServletName() + "'");
1192         }
1193         if (this.throwExceptionIfNoHandlerFound) {
1194             throw new NoHandlerFoundException(request.getMethod(), getRequestUri(request),
1195                     new ServletServerHttpRequest(request).getHeaders());
1196         }
1197         else {
1198             response.sendError(HttpServletResponse.SC_NOT_FOUND);
1199         }
1200     }
1201 
1202     /**
1203      * Return the HandlerAdapter for this handler object.
1204      * 返回handler对象的handler适配器
1205      * @param handler the handler object to find an adapter for
1206      * @throws ServletException if no HandlerAdapter can be found for the handler. This is a fatal error.
1207      */
1208     protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
1209         for (HandlerAdapter ha : this.handlerAdapters) {
1210             if (logger.isTraceEnabled()) {
1211                 logger.trace("Testing handler adapter [" + ha + "]");
1212             }
1213             if (ha.supports(handler)) {
1214                 return ha;
1215             }
1216         }
1217         throw new ServletException("No adapter for handler [" + handler +
1218                 "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
1219     }
1220 
1221     /**
1222      * Determine an error ModelAndView via the registered HandlerExceptionResolvers.
1223      * @param request current HTTP request
1224      * @param response current HTTP response
1225      * @param handler the executed handler, or {@code null} if none chosen at the time of the exception
1226      * (for example, if multipart resolution failed)
1227      * @param ex the exception that got thrown during handler execution
1228      * @return a corresponding ModelAndView to forward to
1229      * @throws Exception if no error ModelAndView found
1230      */
1231     protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
1232             Object handler, Exception ex) throws Exception {
1233 
1234         // Check registered HandlerExceptionResolvers...
1235         ModelAndView exMv = null;
1236         for (HandlerExceptionResolver handlerExceptionResolver : this.handlerExceptionResolvers) {
1237             exMv = handlerExceptionResolver.resolveException(request, response, handler, ex);
1238             if (exMv != null) {
1239                 break;
1240             }
1241         }
1242         if (exMv != null) {
1243             if (exMv.isEmpty()) {
1244                 request.setAttribute(EXCEPTION_ATTRIBUTE, ex);
1245                 return null;
1246             }
1247             // We might still need view name translation for a plain error model...
1248             if (!exMv.hasView()) {
1249                 exMv.setViewName(getDefaultViewName(request));
1250             }
1251             if (logger.isDebugEnabled()) {
1252                 logger.debug("Handler execution resulted in exception - forwarding to resolved error view: " + exMv, ex);
1253             }
1254             WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());
1255             return exMv;
1256         }
1257 
1258         throw ex;
1259     }
1260 
1261     /**
1262      * Render the given ModelAndView.
1263      * <p>This is the last stage in handling a request. It may involve resolving the view by name.
1264      * 根据给定的ModelAndView进行渲染。这是处理请求的最后一步，涉及到通过名称解析视图。
1265      * @param mv the ModelAndView to render
1266      * @param request current HTTP servlet request
1267      * @param response current HTTP servlet response
1268      * @throws ServletException if view is missing or cannot be resolved
1269      * @throws Exception if there's a problem rendering the view
1270      */
1271     protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
1272         // Determine locale for request and apply it to the response.
1273         Locale locale = this.localeResolver.resolveLocale(request);
1274         response.setLocale(locale);
1275 
1276         View view;
1277         //判断是否是视图引用
1278         if (mv.isReference()) {
1279             // We need to resolve the view name.
1280             //将视图名称解析为一个view对象（等待渲染），为null则抛出无法解析异常
1281             view = resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request);
1282             if (view == null) {
1283                 throw new ServletException("Could not resolve view with name '" + mv.getViewName() +
1284                         "' in servlet with name '" + getServletName() + "'");
1285             }
1286         }
1287         else {
1288             // No need to lookup: the ModelAndView object contains the actual View object.
1289             //若是非视图引用，则直接可以从ModelAndView对象中获取真实的View对象
1290             view = mv.getView();
1291             if (view == null) {
1292                 throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +
1293                         "View object in servlet with name '" + getServletName() + "'");
1294             }
1295         }
1296 
1297         // Delegate to the View object for rendering.
1298         //委托到视图对象进行呈现。
1299         if (logger.isDebugEnabled()) {
1300             logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'");
1301         }
1302         try {
1303             if (mv.getStatus() != null) {
1304                 response.setStatus(mv.getStatus().value());//设置http响应状态
1305             }
1306             /**
1307              * The first step will be preparing the request: In the JSP case, this would mean
1308              * setting model objects as request attributes. The second step will be the actual
1309              * rendering of the view, for example including the JSP via a RequestDispatcher.
1310              * 第一步是准备request：如果是jsp页面，则意味着将model对象设置为request属性。第二步
1311              * 将是真正的渲染视图，举例来说，JSP通过一个RequestDispatcher(RequestDispatcher是一个
1312              * Web资源的包装器，可以用来把当前request传递到该资源，或者把新的资源包括到当前响应中。)。
1313             */
1314             view.render(mv.getModelInternal(), request, response);//根据特定的model渲染视图
1315         }
1316         catch (Exception ex) {
1317             if (logger.isDebugEnabled()) {
1318                 logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name '" +
1319                         getServletName() + "'", ex);
1320             }
1321             throw ex;
1322         }
1323     }
1324 
1325     /**
1326      * Translate the supplied request into a default view name.
1327      * 根据提供的请求得到默认的视图名称
1328      * @param request current HTTP servlet request
1329      * @return the view name (or {@code null} if no default found)
1330      * @throws Exception if view name translation failed
1331      */
1332     protected String getDefaultViewName(HttpServletRequest request) throws Exception {
1333         return this.viewNameTranslator.getViewName(request);
1334     }
1335 
1336     /**
1337      * Resolve the given view name into a View object (to be rendered).
1338      * 根据给定的视图名称将其变成一个view对象（等待渲染）
1339      * <p>The default implementations asks all ViewResolvers of this dispatcher.
1340      * Can be overridden for custom resolution strategies, potentially based on
1341      * specific model attributes or request parameters.
1342      * @param viewName the name of the view to resolve
1343      * @param model the model to be passed to the view
1344      * @param locale the current locale
1345      * @param request current HTTP servlet request
1346      * @return the View object, or {@code null} if none found
1347      * @throws Exception if the view cannot be resolved
1348      * (typically in case of problems creating an actual View object)
1349      * @see ViewResolver#resolveViewName
1350      */
1351     protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale,
1352             HttpServletRequest request) throws Exception {
1353         //遍历所有的视图解析器，解析出视图名称
1354         for (ViewResolver viewResolver : this.viewResolvers) {
1355             View view = viewResolver.resolveViewName(viewName, locale);
1356             if (view != null) {
1357                 return view;
1358             }
1359         }
1360         return null;
1361     }
1362 
1363     private void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response,
1364             HandlerExecutionChain mappedHandler, Exception ex) throws Exception {
1365 
1366         if (mappedHandler != null) {
1367             mappedHandler.triggerAfterCompletion(request, response, ex);
1368         }
1369         throw ex;
1370     }
1371 
1372     /**
1373      * Restore the request attributes after an include.
1374      * 重新存储请求中的属性
1375      * @param request current HTTP request
1376      * @param attributesSnapshot the snapshot of the request attributes before the include
1377      */
1378     @SuppressWarnings("unchecked")
1379     private void restoreAttributesAfterInclude(HttpServletRequest request, Map<?,?> attributesSnapshot) {
1380         // Need to copy into separate Collection here, to avoid side effects
1381         // on the Enumeration when removing attributes.
1382         Set<String> attrsToCheck = new HashSet<String>();
1383         Enumeration<?> attrNames = request.getAttributeNames();
1384         while (attrNames.hasMoreElements()) {
1385             String attrName = (String) attrNames.nextElement();
1386             if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
1387                 attrsToCheck.add(attrName);
1388             }
1389         }
1390 
1391         // Add attributes that may have been removed
1392         attrsToCheck.addAll((Set<String>) attributesSnapshot.keySet());
1393 
1394         // Iterate over the attributes to check, restoring the original value
1395         // or removing the attribute, respectively, if appropriate.
1396         for (String attrName : attrsToCheck) {
1397             Object attrValue = attributesSnapshot.get(attrName);
1398             if (attrValue == null){
1399                 request.removeAttribute(attrName);
1400             }
1401             else if (attrValue != request.getAttribute(attrName)) {
1402                 request.setAttribute(attrName, attrValue);
1403             }
1404         }
1405     }
1406 
1407     private static String getRequestUri(HttpServletRequest request) {
1408         String uri = (String) request.getAttribute(WebUtils.INCLUDE_REQUEST_URI_ATTRIBUTE);
1409         if (uri == null) {
1410             uri = request.getRequestURI();
1411         }
1412         return uri;
1413     }
1414 
1415 }