SpringMVC源码解析（一） - 图1

文章结构

  1. 源码阅读环境的搭建
  2. SpringBoot中SpringMVC自动配置原理
  3. DispatcherServlet的初始化逻辑
  4. web容器的初始化

源码阅读环境搭建

为了简单起见，再一个就是现在这个年代也没有啥项目使用JSP了。所以本次分析使用SpringBoot结合thymeleaf来搞

首先pom文件依赖

  1.    <parent>
  2.        <groupId>org.springframework.boot</groupId>
  3.        <artifactId>spring-boot-starter-parent</artifactId>
  4.        <version>2.0.0.RELEASE</version>
  5.    </parent>
  6. <dependency>
  7.            <groupId>org.springframework.boot</groupId>
  8.            <artifactId>spring-boot-starter-web</artifactId>
  9.        </dependency>
  10.        <dependency>
  11.            <groupId>org.springframework.boot</groupId>
  12.            <artifactId>spring-boot-starter-thymeleaf</artifactId>
  13.        </dependency>

application.properties

  1. spring.thymeleaf.prefix=classpath:/templates/
  2. spring.thymeleaf.suffix=.html
  3. spring.thymeleaf.mode=LEGACYHTML5
  4. spring.thymeleaf.encoding=UTF-8
  5. spring.thymeleaf.content-type=text/html
  6. spring.thymeleaf.cache=false

test.html

  1. <!DOCTYPE HTML>
  2. <html xmlns="http://www.w3.org/1999/xhtml" xmlns:th="http://www.thymeleaf.org">
  3. <head>
  4.     <meta content="text/html;charset=UTF-8"/>
  5. </head>
  6. <body>
  7. <span th:text="'用户名：'+${name}+',年龄：'+${age}">
  8. </span>
  9. </body>
  10. </html>

Controller

  1. @Controller
  2. public class MVCDemoController {
  4.     @RequestMapping(value = "/testMVC",method = RequestMethod.GET )
  5.     public String testMVC(Model model){
  6.         model.addAttribute("name","张三");
  7.         model.addAttribute("age","18");
  9.         return "test";
  10.     }
  12. }

启动demo

  1. @SpringBootApplication(scanBasePackages="cn.shiyujun.controller")
  2. public class MVCDemo {
  3.     public static void main (String args[]){
  4.         SpringApplication.run(MVCDemo.class, args);
  5.     }
  6. }

至此Deno工程搭建完毕，有需要源码的同学可以从下方地址获取
https://github.com/shiyujun/spring-framework

源码分析

SpringMVC自动配置

我们知道在SpringBoot中使用SpringMVC的时候是不需要像传统Spring中配置web.xml和配置文件等等的。那么大家知道这是为什么吗

答案就在这个类WebMvcAutoConfiguration里面

  1. @Configuration
  2. @ConditionalOnWebApplication(type = Type.SERVLET)
  3. @ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
  4. @ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
  5. @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
  6. @AutoConfigureAfter({ DispatcherServletAutoConfiguration.class,
  7.         ValidationAutoConfiguration.class })
  8. public class WebMvcAutoConfiguration {
  10.     public static final String DEFAULT_PREFIX = "";
  12.     public static final String DEFAULT_SUFFIX = "";
  14.     private static final String[] SERVLET_LOCATIONS = { "/" };
  16.     @Bean
  17.     @ConditionalOnMissingBean(HiddenHttpMethodFilter.class)
  18.     public OrderedHiddenHttpMethodFilter hiddenHttpMethodFilter() {
  19.         return new OrderedHiddenHttpMethodFilter();
  20.     }
  22.     @Bean
  23.     @ConditionalOnMissingBean(HttpPutFormContentFilter.class)
  24.     @ConditionalOnProperty(prefix = "spring.mvc.formcontent.putfilter", name = "enabled", matchIfMissing = true)
  25.     public OrderedHttpPutFormContentFilter httpPutFormContentFilter() {
  26.         return new OrderedHttpPutFormContentFilter();
  27.     }
  29.     @Configuration
  30.     @Import(EnableWebMvcConfiguration.class)
  31.     @EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class })
  32.     public static class WebMvcAutoConfigurationAdapter
  33.             implements WebMvcConfigurer, ResourceLoaderAware {
  35.         @Bean
  36.         @ConditionalOnMissingBean
  37.         public InternalResourceViewResolver defaultViewResolver() {
  38.             InternalResourceViewResolver resolver = new InternalResourceViewResolver();
  39.             resolver.setPrefix(this.mvcProperties.getView().getPrefix());
  40.             resolver.setSuffix(this.mvcProperties.getView().getSuffix());
  41.             return resolver;
  42.         }
  44.         @Bean
  45.         @ConditionalOnBean(View.class)
  46.         @ConditionalOnMissingBean
  47.         public BeanNameViewResolver beanNameViewResolver() {
  48.             BeanNameViewResolver resolver = new BeanNameViewResolver();
  49.             resolver.setOrder(Ordered.LOWEST_PRECEDENCE - 10);
  50.             return resolver;
  51.         }
  53.         @Bean
  54.         @ConditionalOnBean(ViewResolver.class)
  55.         @ConditionalOnMissingBean(name = "viewResolver", value = ContentNegotiatingViewResolver.class)
  56.         public ContentNegotiatingViewResolver viewResolver(BeanFactory beanFactory) {
  57.             ContentNegotiatingViewResolver resolver = new ContentNegotiatingViewResolver();
  58.             resolver.setContentNegotiationManager(
  59.                     beanFactory.getBean(ContentNegotiationManager.class));
  60.             // ContentNegotiatingViewResolver uses all the other view resolvers to locate
  61.             // a view so it should have a high precedence
  62.             resolver.setOrder(Ordered.HIGHEST_PRECEDENCE);
  63.             return resolver;
  64.         }
  66.         @Bean
  67.         @ConditionalOnMissingBean
  68.         @ConditionalOnProperty(prefix = "spring.mvc", name = "locale")
  69.         public LocaleResolver localeResolver() {
  70.             if (this.mvcProperties
  71.                     .getLocaleResolver() == WebMvcProperties.LocaleResolver.FIXED) {
  72.                 return new FixedLocaleResolver(this.mvcProperties.getLocale());
  73.             }
  74.             AcceptHeaderLocaleResolver localeResolver = new AcceptHeaderLocaleResolver();
  75.             localeResolver.setDefaultLocale(this.mvcProperties.getLocale());
  76.             return localeResolver;
  77.         }
  79.         @Bean
  80.         public WelcomePageHandlerMapping welcomePageHandlerMapping(
  81.                 ApplicationContext applicationContext) {
  82.             return new WelcomePageHandlerMapping(
  83.                     new TemplateAvailabilityProviders(applicationContext),
  84.                     applicationContext, getWelcomePage(),
  85.                     this.mvcProperties.getStaticPathPattern());
  86.         }
  88.         @Bean
  89.         @ConditionalOnMissingBean({ RequestContextListener.class,
  90.                 RequestContextFilter.class })
  91.         public static RequestContextFilter requestContextFilter() {
  92.             return new OrderedRequestContextFilter();
  93.         }
  95.         @Configuration
  96.         @ConditionalOnProperty(value = "spring.mvc.favicon.enabled", matchIfMissing = true)
  97.         public static class FaviconConfiguration implements ResourceLoaderAware {
  99.             @Bean
  100.             public SimpleUrlHandlerMapping faviconHandlerMapping() {
  101.                 SimpleUrlHandlerMapping mapping = new SimpleUrlHandlerMapping();
  102.                 mapping.setOrder(Ordered.HIGHEST_PRECEDENCE + 1);
  103.                 mapping.setUrlMap(Collections.singletonMap("**/favicon.ico",
  104.                         faviconRequestHandler()));
  105.                 return mapping;
  106.             }
  108.             @Bean
  109.             public ResourceHttpRequestHandler faviconRequestHandler() {
  110.                 ResourceHttpRequestHandler requestHandler = new ResourceHttpRequestHandler();
  111.                 requestHandler.setLocations(resolveFaviconLocations());
  112.                 return requestHandler;
  113.             }
  115.         }
  117.     }
  119.     /**
  120.      * Configuration equivalent to {@code @EnableWebMvc}.
  121.      */
  122.     @Configuration
  123.     public static class EnableWebMvcConfiguration extends DelegatingWebMvcConfiguration {
  125.         @Bean
  126.         @Override
  127.         public RequestMappingHandlerAdapter requestMappingHandlerAdapter() {
  128.             RequestMappingHandlerAdapter adapter = super.requestMappingHandlerAdapter();
  129.             adapter.setIgnoreDefaultModelOnRedirect(this.mvcProperties == null
  130.                     || this.mvcProperties.isIgnoreDefaultModelOnRedirect());
  131.             return adapter;
  132.         }
  134.         @Bean
  135.         @Primary
  136.         @Override
  137.         public RequestMappingHandlerMapping requestMappingHandlerMapping() {
  138.             // Must be @Primary for MvcUriComponentsBuilder to work
  139.             return super.requestMappingHandlerMapping();
  140.         }
  142.         @Bean
  143.         @Override
  144.         public FormattingConversionService mvcConversionService() {
  145.             WebConversionService conversionService = new WebConversionService(
  146.                     this.mvcProperties.getDateFormat());
  147.             addFormatters(conversionService);
  148.             return conversionService;
  149.         }
  151.         @Bean
  152.         @Override
  153.         public Validator mvcValidator() {
  154.             if (!ClassUtils.isPresent("javax.validation.Validator",
  155.                     getClass().getClassLoader())) {
  156.                 return super.mvcValidator();
  157.             }
  158.             return ValidatorAdapter.get(getApplicationContext(), getValidator());
  159.         }
  161.         @Bean
  162.         @Override
  163.         public ContentNegotiationManager mvcContentNegotiationManager() {
  164.             ContentNegotiationManager manager = super.mvcContentNegotiationManager();
  165.             List<ContentNegotiationStrategy> strategies = manager.getStrategies();
  166.             ListIterator<ContentNegotiationStrategy> iterator = strategies.listIterator();
  167.             while (iterator.hasNext()) {
  168.                 ContentNegotiationStrategy strategy = iterator.next();
  169.                 if (strategy instanceof PathExtensionContentNegotiationStrategy) {
  170.                     iterator.set(new OptionalPathExtensionContentNegotiationStrategy(
  171.                             strategy));
  172.                 }
  173.             }
  174.             return manager;
  175.         }
  177.     }
  179.     @Configuration
  180.     @ConditionalOnEnabledResourceChain
  181.     static class ResourceChainCustomizerConfiguration {
  183.         @Bean
  184.         public ResourceChainResourceHandlerRegistrationCustomizer resourceHandlerRegistrationCustomizer() {
  185.             return new ResourceChainResourceHandlerRegistrationCustomizer();
  186.         }
  188.     }
  190. }

仔细看这个类，你就会发现这些自动注入的一些类都是之前需要我们在xml文件中配置的，只不过是SpringBoot帮我们做了这个操作。只有当我们需要自定义一些东西的才有必要去关心这些配置，平常使用的时候拿来就用即可。这就是大名鼎鼎的约定大于配置

初始化DispatcherServlet

Tomcat.java
->loadServlet()
->GenericServlet.init()
->Servlet.init()
image.png

DispatcherServlet是一个实现了Servlet接口的类，Servlet的初始化阶段会调用它的init()方法，而DispatcherServlet的方法是继承自父类HttpServletBean的

  1. public final void init() throws ServletException {
  2.         if (logger.isDebugEnabled()) {
  3.             logger.debug("Initializing servlet '" + getServletName() + "'");
  4.         }
  5.           //处理init-param参数，但是SpringBoot中默认是没有的
  6.         PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
  7.         if (!pvs.isEmpty()) {
  8.             try {
  9.                 BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
  10.                 ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
  11.                 bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
  12.                 initBeanWrapper(bw);
  13.                 bw.setPropertyValues(pvs, true);
  14.             }
  15.             catch (BeansException ex) {
  16.                 if (logger.isErrorEnabled()) {
  17.                     logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
  18.                 }
  19.                 throw ex;
  20.             }
  21.         }
  23.         // 初始化Servlet，往下看
  24.         initServletBean();
  26.         if (logger.isDebugEnabled()) {
  27.             logger.debug("Servlet '" + getServletName() + "' configured successfully");
  28.         }
  29.     }
  31. protected final void initServletBean() throws ServletException {
  32.         getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
  33.         if (this.logger.isInfoEnabled()) {
  34.             this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
  35.         }
  36.         long startTime = System.currentTimeMillis();
  38.         try {
  39.               //初始化web容器
  40.             this.webApplicationContext = initWebApplicationContext();
  41.               //扩展点
  42.             initFrameworkServlet();
  43.         }
  44.         catch (ServletException ex) {
  45.             this.logger.error("Context initialization failed", ex);
  46.             throw ex;
  47.         }
  48.         catch (RuntimeException ex) {
  49.             this.logger.error("Context initialization failed", ex);
  50.             throw ex;
  51.         }
  53.         if (this.logger.isInfoEnabled()) {
  54.             long elapsedTime = System.currentTimeMillis() - startTime;
  55.             this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
  56.                     elapsedTime + " ms");
  57.         }
  58.     }

初始化web容器

  1. protected WebApplicationContext initWebApplicationContext() {
  2.           //获取AnnotationConfigServletWebServerApplicationContext类型的web容器
  3.         WebApplicationContext rootContext =
  4.                 WebApplicationContextUtils.getWebApplicationContext(getServletContext());
  5.         WebApplicationContext wac = null;
  7.         if (this.webApplicationContext != null) {
  8.             wac = this.webApplicationContext;
  9.             if (wac instanceof ConfigurableWebApplicationContext) {
  10.                 ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
  11.                 if (!cwac.isActive()) {
  12.                     if (cwac.getParent() == null) {
  13.                         cwac.setParent(rootContext);
  14.                     }
  15.                     configureAndRefreshWebApplicationContext(cwac);
  16.                 }
  17.             }
  18.         }
  19.         if (wac == null) {
  20.             wac = findWebApplicationContext();
  21.         }
  22.         if (wac == null) {
  23.             wac = createWebApplicationContext(rootContext);
  24.         }
  26.         if (!this.refreshEventReceived) {
  27.             // 刷新应用上下文，这里是重点，接着往下看
  28.             onRefresh(wac);
  29.         }
  31.         if (this.publishContext) {
  32.             // 推送事件通知
  33.             String attrName = getServletContextAttributeName();
  34.             getServletContext().setAttribute(attrName, wac);
  35.             if (this.logger.isDebugEnabled()) {
  36.                 this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
  37.                         "' as ServletContext attribute with name [" + attrName + "]");
  38.             }
  39.         }
  41.         return wac;
  42.     }

下面会看到一些熟悉的东西

  1.     protected void onRefresh(ApplicationContext context) {
  2.         initStrategies(context);
  3.     }
  4. protected void initStrategies(ApplicationContext context) {
  5.         initMultipartResolver(context);
  6.         initLocaleResolver(context);
  7.         initThemeResolver(context);
  8.         initHandlerMappings(context);
  9.         initHandlerAdapters(context);
  10.         initHandlerExceptionResolvers(context);
  11.         initRequestToViewNameTranslator(context);
  12.         initViewResolvers(context);
  13.         initFlashMapManager(context);
  14.     }

可以看到上方这一块代码都是一些常用组件的初始化，初始化的逻辑都比较简单，下面随意挑取2个看一下

  1.     private void initMultipartResolver(ApplicationContext context) {
  2.         try {
  3.             this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);
  4.             if (logger.isDebugEnabled()) {
  5.                 logger.debug("Using MultipartResolver [" + this.multipartResolver + "]");
  6.             }
  7.         }
  8.         catch (NoSuchBeanDefinitionException ex) {
  9.             // Default is no multipart resolver.
  10.             this.multipartResolver = null;
  11.             if (logger.isDebugEnabled()) {
  12.                 logger.debug("Unable to locate MultipartResolver with name '" + MULTIPART_RESOLVER_BEAN_NAME +
  13.                         "': no multipart request handling provided");
  14.             }
  15.         }
  16.     }
  17. private void initHandlerMappings(ApplicationContext context) {
  18.         this.handlerMappings = null;
  20.         if (this.detectAllHandlerMappings) {
  21.             // 加载所有实现HandlerMapping接口的bean
  22.             Map<String, HandlerMapping> matchingBeans =
  23.                     BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
  24.             if (!matchingBeans.isEmpty()) {
  25.                 this.handlerMappings = new ArrayList<>(matchingBeans.values());
  26.                 // 排序，Spring处理请求就是根据这个排序的结果进行处理，如果当前handlerMapping不可以处理则抛给下一个
  27.                 AnnotationAwareOrderComparator.sort(this.handlerMappings);
  28.             }
  29.         }
  30.         else {
  31.             try {
  32.                 HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
  33.                 this.handlerMappings = Collections.singletonList(hm);
  34.             }
  35.             catch (NoSuchBeanDefinitionException ex) {
  36.                 // Ignore, we'll add a default HandlerMapping later.
  37.             }
  38.         }
  40.         // Ensure we have at least one HandlerMapping, by registering
  41.         // a default HandlerMapping if no other mappings are found.
  42.         if (this.handlerMappings == null) {
  43.             this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
  44.             if (logger.isDebugEnabled()) {
  45.                 logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
  46.             }
  47.         }
  48.     }

至此，DispatcherServlet的初始化就完成了