Spring源碼解析之SpringMVC源碼解析(一)

一、源碼閱讀環境

用idea快速創建一個springboot 項目 ，在項目添加一個controller 方法，這裡就不寫創建過程了。主要需要以下

啟動類

<code>@SpringBootApplication
public class MVCApplication {
    public static void main (String args[]){
        SpringApplication.run(MVCApplication.class, args);
    }
}
/<code>

Controller

<code>@Controller
public class MVCDemoController {

    @RequestMapping(value = "/testMVC",method = RequestMethod.GET )
    public String testMVC(){
        return "test";
    }
}
/<code>

二、源碼分析

SpringMVC自動配置

我們知道在SpringBoot中使用SpringMVC的時候是不需要像傳統Spring中配置web.xml和配置文件等等的。那麼大家知道這是為什麼嗎

答案就在這個類WebMvcAutoConfiguration裡面 以下代碼為了方便閱讀只保留了部分源碼

<code>@Configuration
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class,
      TaskExecutionAutoConfiguration.class, ValidationAutoConfiguration.class })
public class WebMvcAutoConfiguration {

   public static final String DEFAULT_PREFIX = "";

   public static final String DEFAULT_SUFFIX = "";

   private static final String[] SERVLET_LOCATIONS = { "/" };

   @Bean
   @ConditionalOnMissingBean(HiddenHttpMethodFilter.class)
   @ConditionalOnProperty(prefix = "spring.mvc.hiddenmethod.filter", name = "enabled", matchIfMissing = true)
   public OrderedHiddenHttpMethodFilter hiddenHttpMethodFilter() {
      return new OrderedHiddenHttpMethodFilter();
   }

   @Bean
   @ConditionalOnMissingBean(FormContentFilter.class)
   @ConditionalOnProperty(prefix = "spring.mvc.formcontent.filter", name = "enabled", matchIfMissing = true)
   public OrderedFormContentFilter formContentFilter() {
      return new OrderedFormContentFilter();
   }

   // Defined as a nested config to ensure WebMvcConfigurer is not read when not
   // on the classpath
   @Configuration
   @Import(EnableWebMvcConfiguration.class)
   @EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class })
   @Order(0)
   public static class WebMvcAutoConfigurationAdapter
         implements WebMvcConfigurer, ResourceLoaderAware {

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

      private final ResourceProperties resourceProperties;

      private final WebMvcProperties mvcProperties;

      private final ListableBeanFactory beanFactory;

      private final ObjectProvider<httpmessageconverters> messageConvertersProvider;

      final ResourceHandlerRegistrationCustomizer resourceHandlerRegistrationCustomizer; 


      private ResourceLoader resourceLoader;

      public WebMvcAutoConfigurationAdapter(ResourceProperties resourceProperties,
            WebMvcProperties mvcProperties, ListableBeanFactory beanFactory,
            ObjectProvider<httpmessageconverters> messageConvertersProvider,
            ObjectProvider<resourcehandlerregistrationcustomizer> resourceHandlerRegistrationCustomizerProvider) {
         this.resourceProperties = resourceProperties;
         this.mvcProperties = mvcProperties;
         this.beanFactory = beanFactory;
         this.messageConvertersProvider = messageConvertersProvider;
         this.resourceHandlerRegistrationCustomizer = resourceHandlerRegistrationCustomizerProvider
               .getIfAvailable();
      }

      @Bean
      @ConditionalOnMissingBean
      public InternalResourceViewResolver defaultViewResolver() {
         InternalResourceViewResolver resolver = new InternalResourceViewResolver();
         resolver.setPrefix(this.mvcProperties.getView().getPrefix());
         resolver.setSuffix(this.mvcProperties.getView().getSuffix());
         return resolver;
      }

      @Bean
      @ConditionalOnBean(View.class)
      @ConditionalOnMissingBean
      public BeanNameViewResolver beanNameViewResolver() {
         BeanNameViewResolver resolver = new BeanNameViewResolver();
         resolver.setOrder(Ordered.LOWEST_PRECEDENCE - 10);
         return resolver;
      }

      @Bean
      @ConditionalOnBean(ViewResolver.class)
      @ConditionalOnMissingBean(name = "viewResolver", value = ContentNegotiatingViewResolver.class)
      public ContentNegotiatingViewResolver viewResolver(BeanFactory beanFactory) {
         ContentNegotiatingViewResolver resolver = new ContentNegotiatingViewResolver();
         resolver.setContentNegotiationManager(
               beanFactory.getBean(ContentNegotiationManager.class));
         // ContentNegotiatingViewResolver uses all the other view resolvers to locate
         // a view so it should have a high precedence
         resolver.setOrder(Ordered.HIGHEST_PRECEDENCE);
         return resolver;
      }

      @Bean
      @ConditionalOnMissingBean
      @ConditionalOnProperty(prefix = "spring.mvc", name = "locale")
      public LocaleResolver localeResolver() { 

         if (this.mvcProperties
               .getLocaleResolver() == WebMvcProperties.LocaleResolver.FIXED) {
            return new FixedLocaleResolver(this.mvcProperties.getLocale());
         }
         AcceptHeaderLocaleResolver localeResolver = new AcceptHeaderLocaleResolver();
         localeResolver.setDefaultLocale(this.mvcProperties.getLocale());
         return localeResolver;
      }

      @Bean
      public WelcomePageHandlerMapping welcomePageHandlerMapping(
            ApplicationContext applicationContext) {
         return new WelcomePageHandlerMapping(
               new TemplateAvailabilityProviders(applicationContext),
               applicationContext, getWelcomePage(),
               this.mvcProperties.getStaticPathPattern());
      }

      @Bean
      @ConditionalOnMissingBean({ RequestContextListener.class,
            RequestContextFilter.class })
      @ConditionalOnMissingFilterBean(RequestContextFilter.class)
      public static RequestContextFilter requestContextFilter() {
         return new OrderedRequestContextFilter();
      }

      @Configuration
      @ConditionalOnProperty(value = "spring.mvc.favicon.enabled", matchIfMissing = true)
      public static class FaviconConfiguration implements ResourceLoaderAware {

         private final ResourceProperties resourceProperties;

         private ResourceLoader resourceLoader;

         public FaviconConfiguration(ResourceProperties resourceProperties) {
            this.resourceProperties = resourceProperties;
         }

         @Override
         public void setResourceLoader(ResourceLoader resourceLoader) {
            this.resourceLoader = resourceLoader;
         }

         @Bean
         public SimpleUrlHandlerMapping faviconHandlerMapping() {
            SimpleUrlHandlerMapping mapping = new SimpleUrlHandlerMapping();
            mapping.setOrder(Ordered.HIGHEST_PRECEDENCE + 1);
            mapping.setUrlMap(Collections.singletonMap("**/favicon.ico",
                  faviconRequestHandler()));
            return mapping; 

         }

         @Bean
         public ResourceHttpRequestHandler faviconRequestHandler() {
            ResourceHttpRequestHandler requestHandler = new ResourceHttpRequestHandler();
            requestHandler.setLocations(resolveFaviconLocations());
            return requestHandler;
         }

      }

   }

   /**
    * Configuration equivalent to {@code @EnableWebMvc}.
    */
   @Configuration
   public static class EnableWebMvcConfiguration extends DelegatingWebMvcConfiguration {

      private final WebMvcProperties mvcProperties;

      private final ListableBeanFactory beanFactory;

      private final WebMvcRegistrations mvcRegistrations;

      public EnableWebMvcConfiguration(
            ObjectProvider<webmvcproperties> mvcPropertiesProvider,
            ObjectProvider<webmvcregistrations> mvcRegistrationsProvider,
            ListableBeanFactory beanFactory) {
         this.mvcProperties = mvcPropertiesProvider.getIfAvailable();
         this.mvcRegistrations = mvcRegistrationsProvider.getIfUnique();
         this.beanFactory = beanFactory;
      }

      @Bean
      @Override
      public RequestMappingHandlerAdapter requestMappingHandlerAdapter() {
         RequestMappingHandlerAdapter adapter = super.requestMappingHandlerAdapter();
         adapter.setIgnoreDefaultModelOnRedirect(this.mvcProperties == null
               || this.mvcProperties.isIgnoreDefaultModelOnRedirect());
         return adapter;
      }
      @Bean
      @Primary
      @Override
      public RequestMappingHandlerMapping requestMappingHandlerMapping() {
         // Must be @Primary for MvcUriComponentsBuilder to work
         return super.requestMappingHandlerMapping();
      }
 

      @Bean
      @Override
      public FormattingConversionService mvcConversionService() {
         WebConversionService conversionService = new WebConversionService(
               this.mvcProperties.getDateFormat());
         addFormatters(conversionService);
         return conversionService;
      }

      @Bean
      @Override
      public Validator mvcValidator() {
         if (!ClassUtils.isPresent("javax.validation.Validator",
               getClass().getClassLoader())) {
            return super.mvcValidator();
         }
         return ValidatorAdapter.get(getApplicationContext(), getValidator());
      }

      @Bean
      @Override
      public ContentNegotiationManager mvcContentNegotiationManager() {
         ContentNegotiationManager manager = super.mvcContentNegotiationManager();
         List<contentnegotiationstrategy> strategies = manager.getStrategies();
         ListIterator<contentnegotiationstrategy> iterator = strategies.listIterator();
         while (iterator.hasNext()) {
            ContentNegotiationStrategy strategy = iterator.next();
            if (strategy instanceof PathExtensionContentNegotiationStrategy) {
               iterator.set(new OptionalPathExtensionContentNegotiationStrategy(
                     strategy));
            }
         }
         return manager;
      }

   }

   @Configuration
   @ConditionalOnEnabledResourceChain
   static class ResourceChainCustomizerConfiguration {

      @Bean
      public ResourceChainResourceHandlerRegistrationCustomizer resourceHandlerRegistrationCustomizer() {
         return new ResourceChainResourceHandlerRegistrationCustomizer();
      }
   }
  
\tinterface ResourceHandlerRegistrationCustomizer {

\t\tvoid customize(ResourceHandlerRegistration registration); 


\t}
/<contentnegotiationstrategy>/<contentnegotiationstrategy>/<webmvcregistrations>/<webmvcproperties>/<resourcehandlerregistrationcustomizer>/<httpmessageconverters>/<httpmessageconverters>/<code>

仔細看這個類，你就會發現這些自動注入的一些類都是之前需要我們在xml文件中配置的，現在SpringBoot幫我們做了這個操作。這就是大名鼎鼎的約定大於配置

初始化DispatcherServlet

DispatcherServlet是一個實現了Servlet接口的類，Servlet的初始化階段會調用它的init()方法，而DispatcherServlet的方法是繼承自父類HttpServletBean的

<code>public final void init() throws ServletException {

   // Set bean properties from init parameters.
  //處理init-param參數，但是SpringBoot中默認是沒有的
   PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
   if (!pvs.isEmpty()) {
      try {
         BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
         ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
         bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
         initBeanWrapper(bw);
         bw.setPropertyValues(pvs, true);
      }
      catch (BeansException ex) {
         if (logger.isErrorEnabled()) {
            logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
         }
         throw ex;
      }
   }

   // Let subclasses do whatever initialization they like.
  // 初始化Servlet，往下看
   initServletBean();
}
/<code>

<code>/** 

 * Overridden method of {@link HttpServletBean}, invoked after any bean properties
 * have been set. Creates this servlet's WebApplicationContext.
 */
@Override
protected final void initServletBean() throws ServletException {
   getServletContext().log("Initializing Spring " + getClass().getSimpleName() + " '" + getServletName() + "'");
   if (logger.isInfoEnabled()) {
      logger.info("Initializing Servlet '" + getServletName() + "'");
   }
   long startTime = System.currentTimeMillis();

   try {
      //初始化web容器 重點往下看
      this.webApplicationContext = initWebApplicationContext();
      //擴展點
      initFrameworkServlet();
   }
   catch (ServletException | RuntimeException ex) {
      logger.error("Context initialization failed", ex);
      throw ex;
   }

   if (logger.isDebugEnabled()) {
      String value = this.enableLoggingRequestDetails ?
            "shown which may lead to unsafe logging of potentially sensitive data" :
            "masked to prevent unsafe logging of potentially sensitive data";
      logger.debug("enableLoggingRequestDetails='" + this.enableLoggingRequestDetails +
            "': request parameters and headers will be " + value);
   }

   if (logger.isInfoEnabled()) {
      logger.info("Completed initialization in " + (System.currentTimeMillis() - startTime) + " ms");
   }
}
protected WebApplicationContext initWebApplicationContext() {
  //獲取AnnotationConfigServletWebServerApplicationContext類型的web容器
\t\tWebApplicationContext rootContext =
\t\t\t\tWebApplicationContextUtils.getWebApplicationContext(getServletContext());
\t\tWebApplicationContext wac = null;

\t\tif (this.webApplicationContext != null) {
\t\t\t// A context instance was injected at construction time -> use it
\t\t\twac = this.webApplicationContext;
\t\t\tif (wac instanceof ConfigurableWebApplicationContext) {
\t\t\t\tConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
\t\t\t\tif (!cwac.isActive()) {
\t\t\t\t\t// The context has not yet been refreshed -> provide services such as
\t\t\t\t\t// setting the parent context, setting the application context id, etc 

\t\t\t\t\tif (cwac.getParent() == null) {
\t\t\t\t\t\t// The context instance was injected without an explicit parent -> set
\t\t\t\t\t\t// the root application context (if any; may be null) as the parent
\t\t\t\t\t\tcwac.setParent(rootContext);
\t\t\t\t\t}
\t\t\t\t\tconfigureAndRefreshWebApplicationContext(cwac);
\t\t\t\t}
\t\t\t}
\t\t}
\t\tif (wac == null) {
\t\t\t// No context instance was injected at construction time -> see if one
\t\t\t// has been registered in the servlet context. If one exists, it is assumed
\t\t\t// that the parent context (if any) has already been set and that the
\t\t\t// user has performed any initialization such as setting the context id
\t\t\twac = findWebApplicationContext();
\t\t}
\t\tif (wac == null) {
\t\t\t// No context instance is defined for this servlet -> create a local one
\t\t\twac = createWebApplicationContext(rootContext);
\t\t}

\t\tif (!this.refreshEventReceived) {
\t\t\t// Either the context is not a ConfigurableApplicationContext with refresh
\t\t\t// support or the context injected at construction time had already been
\t\t\t// refreshed -> trigger initial onRefresh manually here.
\t\t\tsynchronized (this.onRefreshMonitor) {
        // 刷新應用上下文，這裡是重點，接著往下看
\t\t\t\tonRefresh(wac);
\t\t\t}
\t\t}

\t\tif (this.publishContext) {
\t\t\t// Publish the context as a servlet context attribute.
      // 推送事件通知
\t\t\tString attrName = getServletContextAttributeName();
\t\t\tgetServletContext().setAttribute(attrName, wac);
\t\t}

\t\treturn wac;
\t}
/<code>

繼續往下看DispatcherServlet中onRefresh

<code>/**
 * This implementation calls {@link #initStrategies}.
 */ 

@Override
protected void onRefresh(ApplicationContext context) {
   initStrategies(context);
}

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

可以看到上方這一塊代碼都是一些常用組件的初始化，初始化的邏輯都比較簡單，隨意挑取2個看一下

<code>private void initHandlerMappings(ApplicationContext context) {
   this.handlerMappings = null;

   if (this.detectAllHandlerMappings) {
      // Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
      Map<string> matchingBeans =
            BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
      if (!matchingBeans.isEmpty()) {
         this.handlerMappings = new ArrayList<>(matchingBeans.values());
         // We keep HandlerMappings in sorted order.
         AnnotationAwareOrderComparator.sort(this.handlerMappings);
      }
   }
   else {
      try {
         HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
         this.handlerMappings = Collections.singletonList(hm); 

      }
      catch (NoSuchBeanDefinitionException ex) {
         // Ignore, we'll add a default HandlerMapping later.
      }
   }

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

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

   if (this.detectAllHandlerAdapters) {
      // Find all HandlerAdapters in the ApplicationContext, including ancestor contexts.
      Map<string> 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");
      }
   }
}
/<string>
/<string>/<code>

至此，DispatcherServlet的初始化就完成了移步

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