SpringMVC源码解析（一）

于 2019-09-04 08:05:00 发布
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分类专栏： Spring源码解析
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本文链接：https://blog.youkuaiyun.com/javaxuexilu/article/details/100738701

注意，读完本篇文章需要很长很长时间

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

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   <parent>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-starter-parent</artifactId>
       <version>2.0.0.RELEASE</version>
   </parent>
<dependency>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter-web</artifactId>
       </dependency>
       <dependency>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter-thymeleaf</artifactId>
       </dependency>

application.properties

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spring.thymeleaf.prefix=classpath:/templates/
spring.thymeleaf.suffix=.html
spring.thymeleaf.mode=LEGACYHTML5
spring.thymeleaf.encoding=UTF-8
spring.thymeleaf.content-type=text/html
spring.thymeleaf.cache=false

test.html

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

Controller

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@Controller
public class MVCDemoController {

    @RequestMapping(value = "/testMVC",method = RequestMethod.GET )
    public String testMVC(Model model){
        model.addAttribute("name","张三");
        model.addAttribute("age","18");

        return "test";
    }

}

启动demo

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

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

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@Configuration
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.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)
	public OrderedHiddenHttpMethodFilter hiddenHttpMethodFilter() {
		return new OrderedHiddenHttpMethodFilter();
	}

	@Bean
	@ConditionalOnMissingBean(HttpPutFormContentFilter.class)
	@ConditionalOnProperty(prefix = "spring.mvc.formcontent.putfilter", name = "enabled", matchIfMissing = true)
	public OrderedHttpPutFormContentFilter httpPutFormContentFilter() {
		return new OrderedHttpPutFormContentFilter();
	}

	@Configuration
	@Import(EnableWebMvcConfiguration.class)
	@EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class })
	public static class WebMvcAutoConfigurationAdapter
			implements WebMvcConfigurer, ResourceLoaderAware {

		@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 })
		public static RequestContextFilter requestContextFilter() {
			return new OrderedRequestContextFilter();
		}

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

			@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 {

		@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();
		}

	}

}

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

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

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public final void init() throws ServletException {
		if (logger.isDebugEnabled()) {
			logger.debug("Initializing servlet '" + getServletName() + "'");
		}
  		//处理init-param参数，但是SpringBoot中默认是没有的
		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;
			}
		}

		// 初始化Servlet，往下看
		initServletBean();

		if (logger.isDebugEnabled()) {
			logger.debug("Servlet '" + getServletName() + "' configured successfully");
		}
	}

protected final void initServletBean() throws ServletException {
		getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
		if (this.logger.isInfoEnabled()) {
			this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
		}
		long startTime = System.currentTimeMillis();

		try {
		  	//初始化web容器
			this.webApplicationContext = initWebApplicationContext();
		  	//扩展点
			initFrameworkServlet();
		}
		catch (ServletException ex) {
			this.logger.error("Context initialization failed", ex);
			throw ex;
		}
		catch (RuntimeException ex) {
			this.logger.error("Context initialization failed", ex);
			throw ex;
		}

		if (this.logger.isInfoEnabled()) {
			long elapsedTime = System.currentTimeMillis() - startTime;
			this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
					elapsedTime + " ms");
		}
	}

初始化web容器

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protected WebApplicationContext initWebApplicationContext() {
  		//获取AnnotationConfigServletWebServerApplicationContext类型的web容器
		WebApplicationContext rootContext =
				WebApplicationContextUtils.getWebApplicationContext(getServletContext());
		WebApplicationContext wac = null;

		if (this.webApplicationContext != null) {
			wac = this.webApplicationContext;
			if (wac instanceof ConfigurableWebApplicationContext) {
				ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
				if (!cwac.isActive()) {
					if (cwac.getParent() == null) {
						cwac.setParent(rootContext);
					}
					configureAndRefreshWebApplicationContext(cwac);
				}
			}
		}
		if (wac == null) {
			wac = findWebApplicationContext();
		}
		if (wac == null) {
			wac = createWebApplicationContext(rootContext);
		}

		if (!this.refreshEventReceived) {
			// 刷新应用上下文，这里是重点，接着往下看
			onRefresh(wac);
		}

		if (this.publishContext) {
			// 推送事件通知
			String attrName = getServletContextAttributeName();
			getServletContext().setAttribute(attrName, wac);
			if (this.logger.isDebugEnabled()) {
				this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
						"' as ServletContext attribute with name [" + attrName + "]");
			}
		}

		return wac;
	}

下面会看到一些熟悉的东西

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	protected void onRefresh(ApplicationContext context) {
		initStrategies(context);
	}
protected void initStrategies(ApplicationContext context) {
		initMultipartResolver(context);
		initLocaleResolver(context);
		initThemeResolver(context);
		initHandlerMappings(context);
		initHandlerAdapters(context);
		initHandlerExceptionResolvers(context);
		initRequestToViewNameTranslator(context);
		initViewResolvers(context);
		initFlashMapManager(context);
	}

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

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	private void initMultipartResolver(ApplicationContext context) {
		try {
			this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);
			if (logger.isDebugEnabled()) {
				logger.debug("Using MultipartResolver [" + this.multipartResolver + "]");
			}
		}
		catch (NoSuchBeanDefinitionException ex) {
			// Default is no multipart resolver.
			this.multipartResolver = null;
			if (logger.isDebugEnabled()) {
				logger.debug("Unable to locate MultipartResolver with name '" + MULTIPART_RESOLVER_BEAN_NAME +
						"': no multipart request handling provided");
			}
		}
	}
private void initHandlerMappings(ApplicationContext context) {
		this.handlerMappings = null;

		if (this.detectAllHandlerMappings) {
			// 加载所有实现HandlerMapping接口的bean
			Map<String, HandlerMapping> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerMappings = new ArrayList<>(matchingBeans.values());
				// 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
				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.isDebugEnabled()) {
				logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
			}
		}
	}

至此，DispatcherServlet的初始化就完成了

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